Pub Date : 2024-06-05DOI: 10.1007/s00162-024-00697-y
Ezhilsabareesh Kannadasan, Callum Atkinson, Julio Soria
Direct numerical simulation (DNS) of turbulent wall-bounded flows requires long streamwise computational domains to establish the correct spatial evolution of large-scale structures with high fidelity. In contrast, experimental measurements can relatively easily capture large-scale structures but struggle to resolve the dissipative flow scales with high fidelity. One methodology to overcome the shortcomings of each approach is by incorporating experimental velocity field measurements into DNS as an inflow boundary condition. This hybrid approach combines the strengths of DNS and experimental measurements, allowing for a reduction in the streamwise computational domain and accelerated development of large-scale structures in turbulent wall-bounded flows. To this end, this paper reports the results of an investigation to establish the impact of limited spatial resolution and limited near-wall experimental inflow data on the DNS of a wall-bounded turbulent shear flow. Specifically, this study investigates the spatial extent required for the DNS of a turbulent channel flow to recover the turbulent velocity fluctuations and energy when experimental inflow data is typically unable to capture fluctuations down to the viscous sub-layer or the smallest viscous scales (i.e. the Kolmogorov scale or their surrogate viscous scale in wall-bounded turbulent shear slows) is used as the inflow to a DNS. A time-resolved numerically generated experimental field is constructed from a periodic channel flow DNS (PCH-DNS) at (Re_{tau } =) 550 and 2300, which is subsequently used as the inflow velocity field for an inflow–outflow boundary conditions DNS. The time-resolved experimental inflow field is generated by appropriately filtering the small scales from the PCH-DNS velocity by integrating over a spatial domain that is representative of a particle image velocimetry interrogation window. This study shows that the recovery of small scales requires a longer domain as the spatial resolution at the inflow decreases with all flow scales recovered and their correct scale-dependent energy is re-established once the flow has developed for 3 channel heights.
湍流壁面流的直接数值模拟(DNS)需要较长的流向计算域,以便高保真地确定大尺度结构的正确空间演化。相比之下,实验测量相对容易捕捉大尺度结构,但难以高保真地解析耗散流尺度。克服两种方法缺点的一种方法是将实验速度场测量结果作为流入边界条件纳入 DNS。这种混合方法结合了 DNS 和实验测量的优势,可以减少流向计算域,加快湍流壁面流中大规模结构的发展。为此,本文报告了一项调查的结果,以确定有限的空间分辨率和有限的近壁实验流入数据对壁界湍流剪切流 DNS 的影响。具体来说,当实验流入数据通常无法捕捉到粘性子层的波动或最小粘性尺度(即科尔莫哥罗夫尺度或壁界湍流剪切慢流中的代粘性尺度)被用作 DNS 的流入量时,本研究调查了湍流通道流 DNS 恢复湍流速度波动和能量所需的空间范围。在 (Re_{tau } =) 550 和 2300 处的周期性通道流 DNS(PCH-DNS)构建了一个时间分辨数值生成的实验场,随后将其用作流入流出边界条件 DNS 的流入速度场。时间分辨实验流入场是通过对粒子图像测速询问窗口的空间域进行积分,对 PCH-DNS 速度中的小尺度进行适当过滤后生成的。这项研究表明,小尺度的恢复需要更长的域,因为流入处的空间分辨率会随着所有流动尺度的恢复而降低,一旦流动发展到 3 个通道高度,就会重新建立正确的尺度相关能量。
{"title":"Investigating the use of 3-component-2-dimensional particle image velocimetry fields as inflow boundary condition for the direct numerical simulation of turbulent channel flow","authors":"Ezhilsabareesh Kannadasan, Callum Atkinson, Julio Soria","doi":"10.1007/s00162-024-00697-y","DOIUrl":"10.1007/s00162-024-00697-y","url":null,"abstract":"<div><p>Direct numerical simulation (DNS) of turbulent wall-bounded flows requires long streamwise computational domains to establish the correct spatial evolution of large-scale structures with high fidelity. In contrast, experimental measurements can relatively easily capture large-scale structures but struggle to resolve the dissipative flow scales with high fidelity. One methodology to overcome the shortcomings of each approach is by incorporating experimental velocity field measurements into DNS as an inflow boundary condition. This hybrid approach combines the strengths of DNS and experimental measurements, allowing for a reduction in the streamwise computational domain and accelerated development of large-scale structures in turbulent wall-bounded flows. To this end, this paper reports the results of an investigation to establish the impact of limited spatial resolution and limited near-wall experimental inflow data on the DNS of a wall-bounded turbulent shear flow. Specifically, this study investigates the spatial extent required for the DNS of a turbulent channel flow to recover the turbulent velocity fluctuations and energy when experimental inflow data is typically unable to capture fluctuations down to the viscous sub-layer or the smallest viscous scales (i.e. the Kolmogorov scale or their surrogate viscous scale in wall-bounded turbulent shear slows) is used as the inflow to a DNS. A time-resolved numerically generated experimental field is constructed from a periodic channel flow DNS (PCH-DNS) at <span>(Re_{tau } =)</span> 550 and 2300, which is subsequently used as the inflow velocity field for an inflow–outflow boundary conditions DNS. The time-resolved experimental inflow field is generated by appropriately filtering the small scales from the PCH-DNS velocity by integrating over a spatial domain that is representative of a particle image velocimetry interrogation window. This study shows that the recovery of small scales requires a longer domain as the spatial resolution at the inflow decreases with all flow scales recovered and their correct scale-dependent energy is re-established once the flow has developed for 3 channel heights.</p></div>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00162-024-00697-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141255153","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-04DOI: 10.1007/s00162-024-00703-3
Vincent Mons, Arthur Vervynck, Olivier Marquet
A combined data-assimilation and linear mean-flow analysis approach is developed to estimate coherent flow fluctuations from limited mean-flow measurements. It also involves Reynolds-Averaged Navier–Stokes (RANS) modelling to efficiently tackle turbulent flows. Considering time-averaged Particle Velocimetry Image (PIV) measurements of the near-stall flow past a NACA0012 airfoil at an angle of attack of (10^{circ }) and in the chord-based Reynolds number range (4.3 cdot 10^4 le Re le 6.4 cdot 10^4), data assimilation is first employed to correct RANS equations that are closed by the Spalart-Allmaras model. The outputs of this procedure are a full mean-flow description that matches the PIV data and a consistent turbulence model that provides not only a mean eddy-viscosity field but also the perturbations of the latter with respect to mean-flow modifications. Global stability and resolvent analyses are then performed based on the so-obtained mean flow and model to satisfactorily predict near-stall low-frequency phenomena, as confirmed through comparison with the Spectral Proper Orthogonal Decomposition (SPOD) of the PIV measurements. This comparison highlights the benefits in taking into account variations in the turbulent eddy-viscosity over a frozen approach for the correct estimation of the present coherent low-frequency oscillations.
摘要 开发了一种数据同化和线性平均流分析相结合的方法,用于从有限的平均流测量中估算相干流波动。该方法还涉及雷诺平均纳维-斯托克斯(RANS)建模,以有效处理湍流。考虑到在攻角为(10^{circ })和基于弦线的雷诺数范围(4.3 cdot 10^4 le Re le 6.4 cdot 10^4)内对经过 NACA0012翼面的近失速流进行的时间平均粒子测速图像(PIV)测量,首先采用数据同化来修正由 Spalart-Allmaras 模型封闭的 RANS 方程。这一程序的输出结果是与 PIV 数据相匹配的完整平均流描述和一致的湍流模型,后者不仅提供平均涡-粘度场,还提供平均流修正时的扰动。然后,根据获得的平均流和模型进行全局稳定性和解析分析,以令人满意地预测近滞留低频现象,这一点通过与 PIV 测量的频谱适当正交分解(SPOD)进行比较得到了证实。这种比较凸显了考虑湍流涡粘度变化比采用冻结方法更有利于正确估计目前的相干低频振荡。
{"title":"Data assimilation and linear analysis with turbulence modelling: application to airfoil stall flows with PIV measurements","authors":"Vincent Mons, Arthur Vervynck, Olivier Marquet","doi":"10.1007/s00162-024-00703-3","DOIUrl":"10.1007/s00162-024-00703-3","url":null,"abstract":"<p>A combined data-assimilation and linear mean-flow analysis approach is developed to estimate coherent flow fluctuations from limited mean-flow measurements. It also involves Reynolds-Averaged Navier–Stokes (RANS) modelling to efficiently tackle turbulent flows. Considering time-averaged Particle Velocimetry Image (PIV) measurements of the near-stall flow past a NACA0012 airfoil at an angle of attack of <span>(10^{circ })</span> and in the chord-based Reynolds number range <span>(4.3 cdot 10^4 le Re le 6.4 cdot 10^4)</span>, data assimilation is first employed to correct RANS equations that are closed by the Spalart-Allmaras model. The outputs of this procedure are a full mean-flow description that matches the PIV data and a consistent turbulence model that provides not only a mean eddy-viscosity field but also the perturbations of the latter with respect to mean-flow modifications. Global stability and resolvent analyses are then performed based on the so-obtained mean flow and model to satisfactorily predict near-stall low-frequency phenomena, as confirmed through comparison with the Spectral Proper Orthogonal Decomposition (SPOD) of the PIV measurements. This comparison highlights the benefits in taking into account variations in the turbulent eddy-viscosity over a frozen approach for the correct estimation of the present coherent low-frequency oscillations.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141255392","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-02DOI: 10.1007/s00162-024-00705-1
Saeed Parvar, Emad Chaparian, Outi Tammisola
A numerical study of yield-stress fluids flowing in porous media is presented. The porous media is randomly constructed by non-overlapping mono-dispersed circular obstacles. Two class of rheological models are investigated: elastoviscoplastic fluids (i.e. Saramito model) and viscoplastic fluids (i.e. Bingham model). A wide range of practical Weissenberg and Bingham numbers is studied at three different levels of porosities of the media. The emphasis is on revealing some physical transport mechanisms of yield-stress fluids in porous media when the elastic behaviour of this kind of fluids is incorporated. Thus, computations of elastoviscoplastic fluids are performed and are compared with the viscoplastic fluid flow properties. At a constant Weissenberg number, the pressure drop increases both with the Bingham number and the solid volume fraction of obstacles. However, the effect of elasticity is less trivial. At low Bingham numbers, the pressure drop of an elastoviscoplastic fluid increases compared to a viscoplastic fluid, while at high Bingham numbers we observe drag reduction by elasticity. At the yield limit (i.e. infinitely large Bingham numbers), elasticity of the fluid systematically promotes yielding: elastic stresses help the fluid to overcome the yield stress resistance at smaller pressure gradients. We observe that elastic effects increase with both Weissenberg and Bingham numbers. In both cases, elastic effects finally make the elastoviscoplastic flow unsteady, which consequently can result in chaos and turbulence.
{"title":"General hydrodynamic features of elastoviscoplastic fluid flows through randomised porous media","authors":"Saeed Parvar, Emad Chaparian, Outi Tammisola","doi":"10.1007/s00162-024-00705-1","DOIUrl":"10.1007/s00162-024-00705-1","url":null,"abstract":"<p>A numerical study of yield-stress fluids flowing in porous media is presented. The porous media is randomly constructed by non-overlapping mono-dispersed circular obstacles. Two class of rheological models are investigated: elastoviscoplastic fluids (i.e. Saramito model) and viscoplastic fluids (i.e. Bingham model). A wide range of practical Weissenberg and Bingham numbers is studied at three different levels of porosities of the media. The emphasis is on revealing some physical transport mechanisms of yield-stress fluids in porous media when the elastic behaviour of this kind of fluids is incorporated. Thus, computations of elastoviscoplastic fluids are performed and are compared with the viscoplastic fluid flow properties. At a constant Weissenberg number, the pressure drop increases both with the Bingham number and the solid volume fraction of obstacles. However, the effect of elasticity is less trivial. At low Bingham numbers, the pressure drop of an elastoviscoplastic fluid increases compared to a viscoplastic fluid, while at high Bingham numbers we observe drag reduction by elasticity. At the yield limit (i.e. infinitely large Bingham numbers), elasticity of the fluid systematically promotes yielding: elastic stresses help the fluid to overcome the yield stress resistance at smaller pressure gradients. We observe that elastic effects increase with both Weissenberg and Bingham numbers. In both cases, elastic effects finally make the elastoviscoplastic flow unsteady, which consequently can result in chaos and turbulence.\u0000</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-06-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00162-024-00705-1.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141191135","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-30DOI: 10.1007/s00162-024-00702-4
Bikash Mahato, Saurabh Saxena, Neda Yaghoobian
Fully resolved direct numerical simulations are used to quantify the effect of evolving heat, due to idealized smoldering processes, on the aerodynamic forces of a spherical particle, representing an idealized fixed-shape firebrand particle. Firebrand particles are small glowing particles that are generated in fires and can be transferred long distances by the wind and create new spot fires. Understanding the transport of firebrands is of great importance in fire science. The simulations are performed at a Reynolds number of 500, relevant for a wide range of firebrand size and wind velocity combinations. The spatiotemporal variation of temperature over the surface of the particle is obtained using a detailed surface energy balance analysis. The firebrand particle is assumed to have the thermal and material properties of pine needles and has a Biot number larger than unity, which means that the particle undergoes notable internal temperature gradients. The results indicate that the buoyancy-induced flow around the particle significantly modifies the trailing vortices and produces two non-interacting tunnel-shaped plumes in the wake of the sphere as the particle’s Richardson number increases. As a result, the particle’s drag and lift coefficients show large deviations from those of a non-heated particle and an isothermal particle. The increased surface temperatures result in an increase in the drag force while inducing a negative lift. The significant variations seen in the aerodynamic forces as a function of the particle’s instantaneous temperature indicate that the influence of the transient thermal conditions of firebrands should be considered in the prediction of the particles’ trajectory and landing spots.
{"title":"Aerodynamic force modifications of a spherical particle with varying temperature: a study of an idealized firebrand","authors":"Bikash Mahato, Saurabh Saxena, Neda Yaghoobian","doi":"10.1007/s00162-024-00702-4","DOIUrl":"10.1007/s00162-024-00702-4","url":null,"abstract":"<p>Fully resolved direct numerical simulations are used to quantify the effect of evolving heat, due to idealized smoldering processes, on the aerodynamic forces of a spherical particle, representing an idealized fixed-shape firebrand particle. Firebrand particles are small glowing particles that are generated in fires and can be transferred long distances by the wind and create new spot fires. Understanding the transport of firebrands is of great importance in fire science. The simulations are performed at a Reynolds number of 500, relevant for a wide range of firebrand size and wind velocity combinations. The spatiotemporal variation of temperature over the surface of the particle is obtained using a detailed surface energy balance analysis. The firebrand particle is assumed to have the thermal and material properties of pine needles and has a Biot number larger than unity, which means that the particle undergoes notable internal temperature gradients. The results indicate that the buoyancy-induced flow around the particle significantly modifies the trailing vortices and produces two non-interacting tunnel-shaped plumes in the wake of the sphere as the particle’s Richardson number increases. As a result, the particle’s drag and lift coefficients show large deviations from those of a non-heated particle and an isothermal particle. The increased surface temperatures result in an increase in the drag force while inducing a negative lift. The significant variations seen in the aerodynamic forces as a function of the particle’s instantaneous temperature indicate that the influence of the transient thermal conditions of firebrands should be considered in the prediction of the particles’ trajectory and landing spots.\u0000</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141190901","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Spreading time, the time that an impacting droplet attains the maximum wetting area on a solid surface, plays a critical role in many engineering applications particularly where heat transfer or chemical reactions are involved. Although the impact dynamics of a droplet significantly differ across the different spreading regimes depending on various collision parameters, it still remains unclear how the spreading time changes for each spreading regime. In the present study, the spreading time during droplet impact on a large spherical target is systematically studied at the three different spreading regimes for a wide range of impact parameters (Weber number, equilibrium contact angle, and Ohnesorge number). The changes of spreading time depending on the impact parameters and underlying physical mechanisms are analyzed in detail at the level of three different spreading regimes. Our results show that the spreading time, proper time scales, dominant impact parameters and associated physical behaviors all significantly and non-linearly change across the three spreading regimes. An improved prediction model for the spreading time is also proposed for each regime, which is now based on only the controllable variables and has an explicit form. Finally, a data-driven prediction model is proposed to represent the complicated and non-linear nature of the spreading time broadly across the three spreading regimes.
{"title":"Numerical investigation of spreading time in droplet impact with a large spherical surface: from physical analysis to data-driven prediction model","authors":"Ikroh Yoon, Seungwon Shin, Damir Juric, Jalel Chergui","doi":"10.1007/s00162-024-00698-x","DOIUrl":"10.1007/s00162-024-00698-x","url":null,"abstract":"<p>Spreading time, the time that an impacting droplet attains the maximum wetting area on a solid surface, plays a critical role in many engineering applications particularly where heat transfer or chemical reactions are involved. Although the impact dynamics of a droplet significantly differ across the different spreading regimes depending on various collision parameters, it still remains unclear how the spreading time changes for each spreading regime. In the present study, the spreading time during droplet impact on a large spherical target is systematically studied at the three different spreading regimes for a wide range of impact parameters (Weber number, equilibrium contact angle, and Ohnesorge number). The changes of spreading time depending on the impact parameters and underlying physical mechanisms are analyzed in detail at the level of three different spreading regimes. Our results show that the spreading time, proper time scales, dominant impact parameters and associated physical behaviors all significantly and non-linearly change across the three spreading regimes. An improved prediction model for the spreading time is also proposed for each regime, which is now based on only the controllable variables and has an explicit form. Finally, a data-driven prediction model is proposed to represent the complicated and non-linear nature of the spreading time broadly across the three spreading regimes.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141111462","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-20DOI: 10.1007/s00162-024-00699-w
Iván Padilla-Montero, Daniel Rodríguez, Vincent Jaunet, Peter Jordan
This work presents a methodology to extract coherent structures from high-speed schlieren images of turbulent twin jets which are more physically interpretable than those obtained with currently existing techniques. Recently, Prasad and Gaitonde (J Fluid Mech 940:1–11, 2022) introduced an approach which employs the momentum potential theory of Doak (J Sound Vib 131(1):67–90, 1989) to compute potential (acoustic and thermal) energy fluctuations from the schlieren images by solving a Poisson equation, and combines it with spectral proper orthogonal decomposition (SPOD) to educe coherent structures from the momentum potential field instead of the original schlieren field. While the latter field is dominated by a broad range of vortical fluctuations in the turbulent mixing region of unheated high-speed jets, the momentum potential field is governed by fluctuations which are intimately related to acoustic emission, and its spatial structure in the frequency domain is very organized. The proposed methodology in this paper improves the technique of Prasad and Gaitonde (J Fluid Mech 940:1–11, 2022) in three new ways. First, the solution of the Poisson equation is carried out in the frequency-wavenumber domain instead of the time-space domain, which simplifies and integrates the solution of the Poisson equation within the SPOD framework based on momentum potential fluctuations. Second, the issue of solving the Poisson equation on a finite domain with ad hoc boundary conditions is explicitly addressed, identifying and removing those unphysical harmonic components introduced in the solution process. Third, the solution of the SPOD problem in terms of momentum potential fluctuations is used to reconstruct schlieren SPOD fields associated with each mode, allowing the visualization of the obtained coherent structures also in terms of the density gradient. The method is applied here to schlieren images of a twin-jet configuration with a small jet separation at two supersonic operation conditions: a perfectly-expanded and an overexpanded one. The SPOD modes based on momentum potential fluctuations retain the wavepacket structure including the direct Mach-wave radiation, together with upstream- and downstream-traveling acoustic waves, similar to SPOD modes based on the schlieren images. However, for the same dataset, they result in a lower-rank decomposition than schlieren-based SPOD and provide an effective separation of twin-jet fluctuations into independent toroidal and flapping oscillations that are recovered as different SPOD modes. These coherent structures are more consistent with twin-jet wavepacket models available in the literature than those originally obtained with direct schlieren-based SPOD, facilitating their interpretation and comparison against theoretical analyses.
本研究提出了一种从湍流孪生射流的高速离散图像中提取相干结构的方法,与现有技术相比,这种方法更能从物理角度解释湍流孪生射流。最近,Prasad 和 Gaitonde(J Fluid Mech 940:1-11,2022 年)介绍了一种方法,该方法采用 Doak 的动量势理论(J Sound Vib 131(1):67-90,1989 年),通过求解泊松方程从 Schlieren 图像中计算势能(声能和热能)波动,并将其与光谱正交分解(SPOD)相结合,从动量势场而非原始 Schlieren 场中提取相干结构。在未加热的高速喷流的湍流混合区域,后一种场受广泛的涡旋波动支配,而动量势场则受与声发射密切相关的波动支配,其频域空间结构非常有条理。本文提出的方法从三个方面改进了 Prasad 和 Gaitonde 的技术(J Fluid Mech 940:1-11, 2022)。首先,泊松方程的求解是在频率-波数域而非时空域中进行的,这简化并整合了基于动量势能波动的 SPOD 框架内的泊松方程求解。其次,明确解决了在有限域上利用特设边界条件求解泊松方程的问题,识别并消除了求解过程中引入的非物理谐波成分。第三,用动量势能波动求解 SPOD 问题,重建与每种模式相关的离层 SPOD 场,使获得的相干结构在密度梯度方面也可视化。该方法适用于在两种超音速运行条件(完全膨胀和过度膨胀)下具有较小射流分离的双射流配置的离散图像。基于动量势能波动的 SPOD 模式保留了波包结构,包括直接的马赫波辐射,以及上游和下游传播的声波,这与基于裂片图像的 SPOD 模式相似。然而,对于相同的数据集,它们的分解阶数比基于施利连的 SPOD 低,并能有效地将双喷流波动分离为独立的环状振荡和拍击振荡,这些振荡被复原为不同的 SPOD 模式。这些相干结构与文献中已有的双喷流波包模型相比,更符合最初用基于schlieren的直接SPOD方法得到的结果,便于解释和与理论分析进行比较。
{"title":"Eduction of coherent structures from schlieren images of twin jets using SPOD informed with momentum potential theory in the spectral domain","authors":"Iván Padilla-Montero, Daniel Rodríguez, Vincent Jaunet, Peter Jordan","doi":"10.1007/s00162-024-00699-w","DOIUrl":"10.1007/s00162-024-00699-w","url":null,"abstract":"<p>This work presents a methodology to extract coherent structures from high-speed schlieren images of turbulent twin jets which are more physically interpretable than those obtained with currently existing techniques. Recently, Prasad and Gaitonde (J Fluid Mech 940:1–11, 2022) introduced an approach which employs the momentum potential theory of Doak (J Sound Vib 131(1):67–90, 1989) to compute potential (acoustic and thermal) energy fluctuations from the schlieren images by solving a Poisson equation, and combines it with spectral proper orthogonal decomposition (SPOD) to educe coherent structures from the momentum potential field instead of the original schlieren field. While the latter field is dominated by a broad range of vortical fluctuations in the turbulent mixing region of unheated high-speed jets, the momentum potential field is governed by fluctuations which are intimately related to acoustic emission, and its spatial structure in the frequency domain is very organized. The proposed methodology in this paper improves the technique of Prasad and Gaitonde (J Fluid Mech 940:1–11, 2022) in three new ways. First, the solution of the Poisson equation is carried out in the frequency-wavenumber domain instead of the time-space domain, which simplifies and integrates the solution of the Poisson equation within the SPOD framework based on momentum potential fluctuations. Second, the issue of solving the Poisson equation on a finite domain with <i>ad hoc</i> boundary conditions is explicitly addressed, identifying and removing those unphysical harmonic components introduced in the solution process. Third, the solution of the SPOD problem in terms of momentum potential fluctuations is used to reconstruct schlieren SPOD fields associated with each mode, allowing the visualization of the obtained coherent structures also in terms of the density gradient. The method is applied here to schlieren images of a twin-jet configuration with a small jet separation at two supersonic operation conditions: a perfectly-expanded and an overexpanded one. The SPOD modes based on momentum potential fluctuations retain the wavepacket structure including the direct Mach-wave radiation, together with upstream- and downstream-traveling acoustic waves, similar to SPOD modes based on the schlieren images. However, for the same dataset, they result in a lower-rank decomposition than schlieren-based SPOD and provide an effective separation of twin-jet fluctuations into independent toroidal and flapping oscillations that are recovered as different SPOD modes. These coherent structures are more consistent with twin-jet wavepacket models available in the literature than those originally obtained with direct schlieren-based SPOD, facilitating their interpretation and comparison against theoretical analyses.\u0000</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00162-024-00699-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141120520","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-20DOI: 10.1007/s00162-024-00700-6
Benjamin Bugeat, Ugur Karban, Anurag Agarwal, Lutz Lesshafft, Peter Jordan
We perform a resolvent analysis of a compressible turbulent jet, where the optimisation domain of the response modes is located in the acoustic field, excluding the hydrodynamic region, in order to promote acoustically efficient modes. We examine the properties of the acoustic resolvent and assess its potential for jet-noise modelling, focusing on the subsonic regime. Resolvent forcing modes, consistent with previous studies, are found to contain supersonic waves associated with Mach wave radiation in the response modes. This differs from the standard resolvent in which hydrodynamic instabilities dominate. We compare resolvent modes with SPOD modes educed from LES data. Acoustic resolvent response modes generally have better alignment with acoustic SPOD modes than standard resolvent response modes. For the optimal mode, the angle of the acoustic beam is close to that found in SPOD modes for moderate frequencies. However, there is no significant separation between the singular values of the leading and sub-optimal modes. Some suboptimal modes are furthermore shown to contain irrelevant structure for jet noise. Thus, even though it contains essential acoustic features absent from the standard resolvent approach, the SVD of the acoustic resolvent alone is insufficient to educe a low-rank model for jet noise. But because it identifies the prevailing mechanisms of jet noise, it provides valuable guidelines in the search of a forcing model (Karban et al. in J Fluid Mech 965:18, 2023).
摘要 我们对可压缩湍流射流进行了解析分析,其中响应模式的优化域位于声场中,不包括流体动力区域,以促进声学高效模式。我们研究了声学解析力的特性,并评估了其在射流噪声建模方面的潜力,重点是亚音速系统。与之前的研究一致,我们发现在响应模式中包含与马赫波辐射相关的超音速波。这与流体力学不稳定性占主导地位的标准解析模式不同。我们将解析模式与根据 LES 数据得出的 SPOD 模式进行了比较。与标准解析响应模式相比,声学解析响应模式通常能更好地与声学 SPOD 模式保持一致。对于最佳模式,声束角度接近于中等频率的 SPOD 模式。但是,领先模式和次优模式的奇异值之间没有明显的差别。此外,一些次优模式还包含与喷气噪声无关的结构。因此,尽管它包含了标准解析量方法所没有的基本声学特征,但仅靠声学解析量的 SVD 并不足以建立喷气噪声的低阶模型。但由于它确定了喷气噪声的主要机制,因此为寻找强迫模型提供了宝贵的指导(Karban 等人,载于《流体力学》965:18, 2023)。
{"title":"Acoustic resolvent analysis of turbulent jets","authors":"Benjamin Bugeat, Ugur Karban, Anurag Agarwal, Lutz Lesshafft, Peter Jordan","doi":"10.1007/s00162-024-00700-6","DOIUrl":"10.1007/s00162-024-00700-6","url":null,"abstract":"<p>We perform a resolvent analysis of a compressible turbulent jet, where the optimisation domain of the response modes is located in the acoustic field, excluding the hydrodynamic region, in order to promote acoustically efficient modes. We examine the properties of the acoustic resolvent and assess its potential for jet-noise modelling, focusing on the subsonic regime. Resolvent forcing modes, consistent with previous studies, are found to contain supersonic waves associated with Mach wave radiation in the response modes. This differs from the standard resolvent in which hydrodynamic instabilities dominate. We compare resolvent modes with SPOD modes educed from LES data. Acoustic resolvent response modes generally have better alignment with acoustic SPOD modes than standard resolvent response modes. For the optimal mode, the angle of the acoustic beam is close to that found in SPOD modes for moderate frequencies. However, there is no significant separation between the singular values of the leading and sub-optimal modes. Some suboptimal modes are furthermore shown to contain irrelevant structure for jet noise. Thus, even though it contains essential acoustic features absent from the standard resolvent approach, the SVD of the acoustic resolvent alone is insufficient to educe a low-rank model for jet noise. But because it identifies the prevailing mechanisms of jet noise, it provides valuable guidelines in the search of a forcing model (Karban et al. in J Fluid Mech 965:18, 2023).\u0000</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00162-024-00700-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141152133","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-18DOI: 10.1007/s00162-024-00694-1
Ali Farghadan, Junoh Jung, Rutvij Bhagwat, Aaron Towne
We present an extension of the RSVD-(Delta t) algorithm initially developed for resolvent analysis of statistically stationary flows to handle harmonic resolvent analysis of time-periodic flows. The harmonic resolvent operator, as proposed by Padovan et al. (J Fluid Mech 900, 2020), characterizes the linearized dynamics of time-periodic flows in the frequency domain, and its singular value decomposition reveals forcing and response modes with optimal energetic gain. However, computing harmonic resolvent modes poses challenges due to (i) the coupling of all (N_{omega }) retained frequencies into a single harmonic resolvent operator and (ii) the singularity or near-singularity of the operator, making harmonic resolvent analysis considerably more computationally expensive than a standard resolvent analysis. To overcome these challenges, the RSVD-(Delta t) algorithm leverages time stepping of the underlying time-periodic linearized Navier–Stokes operator, which is (N_{omega }) times smaller than the harmonic resolvent operator, to compute the action of the harmonic resolvent operator. We develop strategies to minimize the algorithm’s CPU and memory consumption, and our results demonstrate that these costs scale linearly with the problem dimension. We validate the RSVD-(Delta t) algorithm by computing modes for a periodically varying Ginzburg–Landau equation and demonstrate its performance using the flow over an airfoil.
{"title":"Efficient harmonic resolvent analysis via time stepping","authors":"Ali Farghadan, Junoh Jung, Rutvij Bhagwat, Aaron Towne","doi":"10.1007/s00162-024-00694-1","DOIUrl":"10.1007/s00162-024-00694-1","url":null,"abstract":"<p>We present an extension of the RSVD-<span>(Delta t)</span> algorithm initially developed for resolvent analysis of statistically stationary flows to handle harmonic resolvent analysis of time-periodic flows. The harmonic resolvent operator, as proposed by Padovan et al. (J Fluid Mech 900, 2020), characterizes the linearized dynamics of time-periodic flows in the frequency domain, and its singular value decomposition reveals forcing and response modes with optimal energetic gain. However, computing harmonic resolvent modes poses challenges due to (i) the coupling of all <span>(N_{omega })</span> retained frequencies into a single harmonic resolvent operator and (ii) the singularity or near-singularity of the operator, making harmonic resolvent analysis considerably more computationally expensive than a standard resolvent analysis. To overcome these challenges, the RSVD-<span>(Delta t)</span> algorithm leverages time stepping of the underlying time-periodic linearized Navier–Stokes operator, which is <span>(N_{omega })</span> times smaller than the harmonic resolvent operator, to compute the action of the harmonic resolvent operator. We develop strategies to minimize the algorithm’s CPU and memory consumption, and our results demonstrate that these costs scale linearly with the problem dimension. We validate the RSVD-<span>(Delta t)</span> algorithm by computing modes for a periodically varying Ginzburg–Landau equation and demonstrate its performance using the flow over an airfoil.\u0000</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-05-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141062857","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-13DOI: 10.1007/s00162-024-00696-z
David Kibe Muchiri, James N. Hewett, Mathieu Sellier, Miguel Moyers-Gonzalez, Jerome Monnier
This paper presents simulations of dam-break flows of Herschel–Bulkley viscoplastic fluids over complex topographies using the shallow water equations (SWE). In particular, this study aims to assess the effects of rheological parameters: power-law index (n), consistency index (K), and yield stress ((tau _{c})), on flow height and velocity over different topographies. Three practical examples of dam-break flow cases are considered: a dam-break on an inclined flat surface, a dam-break over a non-flat topography, and a dam-break over a wet bed (downstream containing an initial fluid level). The effects of bed slope and depth ratios (the ratio between upstream and downstream fluid levels) on flow behaviour are also analyzed. The numerical results are compared with experimental data from the literature and are found to be in good agreement. Results show that for both dry and wet bed conditions, the fluid front position, peak height, and mean velocity decrease when any of the three rheological parameters are increased. However, based on a parametric sensitivity analysis, the power-law index appears to be the dominant factor in dictating fluid behaviour. Moreover, by increasing the bed slope and/or depth ratio, the wave-frontal position moves further downstream. Furthermore, the presence of an obstacle is observed to cause the formation of an upsurge that moves in the upstream direction, which increases by increasing any of the three rheological parameters. This study is useful for an in-depth understanding of the effects of rheology on catastrophic gravity-driven flows of non-Newtonian fluids (like lava or mud flows) for risk assessment and mitigation.
{"title":"Numerical simulations of dam-break flows of viscoplastic fluids via shallow water equations","authors":"David Kibe Muchiri, James N. Hewett, Mathieu Sellier, Miguel Moyers-Gonzalez, Jerome Monnier","doi":"10.1007/s00162-024-00696-z","DOIUrl":"10.1007/s00162-024-00696-z","url":null,"abstract":"<p>This paper presents simulations of dam-break flows of Herschel–Bulkley viscoplastic fluids over complex topographies using the shallow water equations (SWE). In particular, this study aims to assess the effects of rheological parameters: power-law index (<i>n</i>), consistency index (<i>K</i>), and yield stress (<span>(tau _{c})</span>), on flow height and velocity over different topographies. Three practical examples of dam-break flow cases are considered: a dam-break on an inclined flat surface, a dam-break over a non-flat topography, and a dam-break over a wet bed (downstream containing an initial fluid level). The effects of bed slope and depth ratios (the ratio between upstream and downstream fluid levels) on flow behaviour are also analyzed. The numerical results are compared with experimental data from the literature and are found to be in good agreement. Results show that for both dry and wet bed conditions, the fluid front position, peak height, and mean velocity decrease when any of the three rheological parameters are increased. However, based on a parametric sensitivity analysis, the power-law index appears to be the dominant factor in dictating fluid behaviour. Moreover, by increasing the bed slope and/or depth ratio, the wave-frontal position moves further downstream. Furthermore, the presence of an obstacle is observed to cause the formation of an upsurge that moves in the upstream direction, which increases by increasing any of the three rheological parameters. This study is useful for an in-depth understanding of the effects of rheology on catastrophic gravity-driven flows of non-Newtonian fluids (like lava or mud flows) for risk assessment and mitigation.\u0000</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00162-024-00696-z.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140934803","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-01DOI: 10.1007/s00162-024-00693-2
Yanting Liu, Nan Deng, Bernd R. Noack, Xin Wang
We numerically investigate the fluidic pinball under symmetric forcing and find seven flow regimes under different rotation speeds. The fluidic pinball consists of three rotatable cylinders placed at the vertices of an equilateral triangle pointing upstream in a uniform oncoming flow. The starting point is the unforced asymmetric periodic vortex shedding at Reynolds number Re = 100 based on the cylinder diameter. The flow is symmetrically actuated by rotating the two rear cylinders at constant speed |b| up to three times the oncoming velocity in both directions. Counterclockwise (b > 0) and clockwise (b < 0) rotation of the bottom cylinder correspond to boat tailing and base bleeding, respectively. A total of seven distinct flow regimes are observed, including a steady flow, three symmetric/asymmetric periodic types of shedding, two symmetric/asymmetric quasi-periodic behaviors, and a chaotic dynamics. The vortex shedding features multiple coupled oscillator modes, including in-phase, anti-phase, and out-of-phase synchronization and non-synchronization. These shedding regimes are analyzed employing the temporal evolution of the aerodynamic forces and a dynamical mode decomposition of the wake flow. The kaleidoscope of unforced and forced dynamics promotes the fluidic pinball as a challenging modeling and control benchmark.
摘要 我们对对称强迫下的流体弹球进行了数值研究,发现了不同旋转速度下的七种流动状态。流体弹球由三个可旋转的圆柱体组成,圆柱体位于等边三角形的顶点,指向匀速来流的上游。起点是雷诺数 Re = 100 时基于圆柱体直径的非受力非对称周期性涡流脱落。通过以恒定速度 |b| 旋转两个后气缸,使气流在两个方向上的速度均达到来流速度的三倍,从而对称地驱动气流。底部圆筒的逆时针(b >0)和顺时针(b <0)旋转分别对应于船尾和船底出血。共观察到七种不同的流态,包括稳定流、三种对称/非对称周期类型的脱落、两种对称/非对称准周期行为和一种混沌动力学。涡流脱落具有多种耦合振荡器模式,包括同相、反相、失相同步和非同步。利用空气动力的时间演变和尾流的动力学模式分解分析了这些脱落状态。非受迫和受迫动力学万花筒促使流体弹球成为具有挑战性的建模和控制基准。
{"title":"The fluidic pinball with symmetric forcing displays steady, periodic, quasi-periodic, and chaotic dynamics","authors":"Yanting Liu, Nan Deng, Bernd R. Noack, Xin Wang","doi":"10.1007/s00162-024-00693-2","DOIUrl":"10.1007/s00162-024-00693-2","url":null,"abstract":"<p>We numerically investigate the fluidic pinball under symmetric forcing and find seven flow regimes under different rotation speeds. The fluidic pinball consists of three rotatable cylinders placed at the vertices of an equilateral triangle pointing upstream in a uniform oncoming flow. The starting point is the unforced asymmetric periodic vortex shedding at Reynolds number Re = 100 based on the cylinder diameter. The flow is symmetrically actuated by rotating the two rear cylinders at constant speed |<i>b</i>| up to three times the oncoming velocity in both directions. Counterclockwise (<i>b</i> > 0) and clockwise (<i>b</i> < 0) rotation of the bottom cylinder correspond to boat tailing and base bleeding, respectively. A total of seven distinct flow regimes are observed, including a steady flow, three symmetric/asymmetric periodic types of shedding, two symmetric/asymmetric quasi-periodic behaviors, and a chaotic dynamics. The vortex shedding features multiple coupled oscillator modes, including in-phase, anti-phase, and out-of-phase synchronization and non-synchronization. These shedding regimes are analyzed employing the temporal evolution of the aerodynamic forces and a dynamical mode decomposition of the wake flow. The kaleidoscope of unforced and forced dynamics promotes the fluidic pinball as a challenging modeling and control benchmark.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140828280","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}