Pub Date : 2024-09-11DOI: 10.1088/1873-7005/ad73ff
Rakesh Kumar and Tanya Sharma
The present work examines the linear stability of non-linear convected flow inside a Riga plate channel. The channel is filled with hybrid nanoliquid and is under the novel influence of the partial slip phenomenon in the present scenario. The left domain of the channel is supported by the Riga sheet whereas the right part is bounded by a sheet of slippery nature. The stability model for this partial slip mechanism is developed in the form of an eigenvalue problem which is explored via the Chebyshev pseudospectral method in combination with the QZ-algorithm. It is reported that the convection forces in hybrid nanofluid are amplified with Riga magnetic number (Hr) under slip/no-slip assumptions. It is interestingly noted that the flow is destabilized by 11.47 with non-linear convection (Nc) when considering no-slip at the right-hand sheet. However, the stability region is enlarged with Nc by 9.53 in the presence of slip at the right-hand sheet. The partial-slip (γ) assumption in the channel decelerates the growth rate of disturbances. The increment in -nanoparticles over the fixed volume of -nanoparticles hampers the instability of the hybrid nanofluid mixture.
{"title":"Stability examination of non-linear convection flow with partial slip phenomenon in a Riga plate channel","authors":"Rakesh Kumar and Tanya Sharma","doi":"10.1088/1873-7005/ad73ff","DOIUrl":"https://doi.org/10.1088/1873-7005/ad73ff","url":null,"abstract":"The present work examines the linear stability of non-linear convected flow inside a Riga plate channel. The channel is filled with hybrid nanoliquid and is under the novel influence of the partial slip phenomenon in the present scenario. The left domain of the channel is supported by the Riga sheet whereas the right part is bounded by a sheet of slippery nature. The stability model for this partial slip mechanism is developed in the form of an eigenvalue problem which is explored via the Chebyshev pseudospectral method in combination with the QZ-algorithm. It is reported that the convection forces in hybrid nanofluid are amplified with Riga magnetic number (Hr) under slip/no-slip assumptions. It is interestingly noted that the flow is destabilized by 11.47 with non-linear convection (Nc) when considering no-slip at the right-hand sheet. However, the stability region is enlarged with Nc by 9.53 in the presence of slip at the right-hand sheet. The partial-slip (γ) assumption in the channel decelerates the growth rate of disturbances. The increment in -nanoparticles over the fixed volume of -nanoparticles hampers the instability of the hybrid nanofluid mixture.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":"12 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142224235","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2024-09-11DOI: 10.1088/1873-7005/ad7400
Muthana Mraweh Khairi, Seyed Esmail Razavi, Faramarz Talati and Mir Biuok Ehghaghi Bonab
In this research, a three-dimensional turbulent wall jet was modeled using an Improved Delayed Detached Eddy Simulation to examine its flow and thermal properties. The accuracy of the simulation was confirmed by comparing key flow characteristics with experimental data. The study involved introducing an oscillating wall and a hot wall within the computational domain to observe their effects on thermal behavior and turbulence structure. OpenFOAM v2012 was utilized for the simulations based on a 3D channel design. The turbulent structure exhibited distinct separated, small-scale, and large-scale turbulence within the domain. The findings indicated that reducing the computational domain height increased the Nusselt number, and positioning the hot wall near the core of the jet also increased the Nusselt number. Additionally, increasing the frequency and amplitude of the oscillating wall resulted in a higher Nusselt number. These results contribute to a deeper understanding of the fluid physics in this specific scenario and can enhance knowledge in the fields of solid and turbulence fluid structure interaction. The analysis of the turbulence structure revealed that a lower domain height created elongated turbulence structures, and placing the hot wall at the end of the computational domain had less impact on smoothing the turbulence structures due to the presence of very strong, large turbulence structures.
{"title":"Effects of oscillated wall on the turbulent structure and heat transfer of three-dimensional wall jet","authors":"Muthana Mraweh Khairi, Seyed Esmail Razavi, Faramarz Talati and Mir Biuok Ehghaghi Bonab","doi":"10.1088/1873-7005/ad7400","DOIUrl":"https://doi.org/10.1088/1873-7005/ad7400","url":null,"abstract":"In this research, a three-dimensional turbulent wall jet was modeled using an Improved Delayed Detached Eddy Simulation to examine its flow and thermal properties. The accuracy of the simulation was confirmed by comparing key flow characteristics with experimental data. The study involved introducing an oscillating wall and a hot wall within the computational domain to observe their effects on thermal behavior and turbulence structure. OpenFOAM v2012 was utilized for the simulations based on a 3D channel design. The turbulent structure exhibited distinct separated, small-scale, and large-scale turbulence within the domain. The findings indicated that reducing the computational domain height increased the Nusselt number, and positioning the hot wall near the core of the jet also increased the Nusselt number. Additionally, increasing the frequency and amplitude of the oscillating wall resulted in a higher Nusselt number. These results contribute to a deeper understanding of the fluid physics in this specific scenario and can enhance knowledge in the fields of solid and turbulence fluid structure interaction. The analysis of the turbulence structure revealed that a lower domain height created elongated turbulence structures, and placing the hot wall at the end of the computational domain had less impact on smoothing the turbulence structures due to the presence of very strong, large turbulence structures.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":"7 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142185245","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Analysis methods based on mode decomposition have been proposed to describe the characteristics of flow phenomena. Among them, proper orthogonal decomposition (POD), which decomposes modes into eigenvalues and basis vectors, has long been used. Many studies have shown that POD is a useful method for capturing the characteristics of unsteady flow. In particular, Snapshot POD has attracted much recent attention and has been used to solve unsteady flow problems. However, the basis vectors of the mode obtained by conventional POD is different for each condition. Therefore, whether the basis vectors of each mode are switching in the direction of parameters (e.g. different shapes or different Reynolds numbers) or whether they develop or decay is difficult to discuss. As a result, discussions on conventional POD tend to be qualitative. To address this issue, the present study uses Parametric Global POD, a method that perfectly matches basis vectors in results with different parameters (in this study, different Reynolds numbers). Parametric Global POD method was applied to the analysis of the flow field in a curved pipe and found to capture the development or decay of modes with major basis vectors in the direction of parameters, which is difficult to achieve with conventional POD methods.
人们提出了基于模式分解的分析方法来描述流动现象的特征。其中，将模态分解为特征值和基矢量的正交分解法（POD）一直被广泛使用。许多研究表明，POD 是捕捉非稳态流动特征的有效方法。其中，快照 POD 近来备受关注，并被用于解决非稳态流动问题。然而，传统 POD 所得到的模态基向量在每个条件下都是不同的。因此，很难讨论每种模式的基向量是否在参数方向上发生切换（如不同形状或不同雷诺数），或者是发展还是衰减。因此，对传统 POD 的讨论往往是定性的。为解决这一问题，本研究采用了参数全局 POD 法，该方法可完美匹配不同参数（本研究中为不同雷诺数）结果中的基向量。将参数全局 POD 方法应用于分析弯曲管道中的流场，发现该方法可以捕捉到主要基向量在参数方向上的模态发展或衰减，而传统的 POD 方法很难实现这一点。
{"title":"Mode analysis for multiple parameter conditions of nozzle internal unsteady flow using Parametric Global Proper Orthogonal Decomposition","authors":"Mikimasa Kawaguchi, Masato Iwasaki, Ryoutaro Nakayama, Ryo Yamamoto, Akira Nakashima, Yoichi Ogata","doi":"10.1088/1873-7005/ad716a","DOIUrl":"https://doi.org/10.1088/1873-7005/ad716a","url":null,"abstract":"Analysis methods based on mode decomposition have been proposed to describe the characteristics of flow phenomena. Among them, proper orthogonal decomposition (POD), which decomposes modes into eigenvalues and basis vectors, has long been used. Many studies have shown that POD is a useful method for capturing the characteristics of unsteady flow. In particular, Snapshot POD has attracted much recent attention and has been used to solve unsteady flow problems. However, the basis vectors of the mode obtained by conventional POD is different for each condition. Therefore, whether the basis vectors of each mode are switching in the direction of parameters (e.g. different shapes or different Reynolds numbers) or whether they develop or decay is difficult to discuss. As a result, discussions on conventional POD tend to be qualitative. To address this issue, the present study uses Parametric Global POD, a method that perfectly matches basis vectors in results with different parameters (in this study, different Reynolds numbers). Parametric Global POD method was applied to the analysis of the flow field in a curved pipe and found to capture the development or decay of modes with major basis vectors in the direction of parameters, which is difficult to achieve with conventional POD methods.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":"27 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142185246","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2024-08-27DOI: 10.1088/1873-7005/ad6a38
Raju Bag, Prabir Kumar Kundu
The purpose of this article is to invent the impact of inconstant properties of fluids on the nanofluidic stream towards the stagnation area of a revolving sphere. The motion is treated as an unsteady radiated flow with a nonlinear sort of heat radiation. It is presumed to have Brownian motion & thermophoretic impact in our flow model. Additionally, a variable magnetic influence is addressed perpendicularly on the spherical surface. A suitable alteration has been applied to make dimensionless of our prime flow profiles. The translated equations and the limiting restrictions are solved through a numerical approach. The well established method RK4 Shooting technique is utilized here with Maple 2017 software. In the exploration of the consequences of requisite parameters on thermal, concentration, and flow features, numerous schematics are involved. The nature of physical quantities like Nusselt numbers, friction coefficients, and Sherwood numbers is stated in a tabular manner. It is perceived from the outcomes that the fluid velocity towards the x-direction is reduced for the variable viscosity parameter, whereas the unsteadiness parameter promotes it. The enhancement of inconstant thermal conductivity brings a positive influence on the thermal profile of fluid. Nusselt number drops against the thermal radiation & variable viscosity with a rates 4.50% and 25.88% correspondingly.
本文旨在研究流体的不稳定特性对纳米流体流向旋转球体停滞区的影响。该运动被视为具有非线性热辐射的不稳定辐射流。在我们的流动模型中，假定它具有布朗运动 & 热传导影响。此外，还处理了垂直于球面的可变磁场影响。我们对主要流动剖面进行了适当的修改，以实现无量纲化。转化方程和限制条件通过数值方法求解。这里使用的是 Maple 2017 软件中成熟的 RK4 射击技术。在探索必要参数对热量、浓度和流动特征的影响时，涉及到许多示意图。努塞尔特数、摩擦系数和舍伍德数等物理量的性质以表格形式列出。从结果中可以看出，在粘度参数可变的情况下，流体向 x 方向的速度会降低，而不稳定性参数则会提高。不稳定热导率的增强对流体的热曲线产生了积极影响。在热辐射& 和可变粘度的作用下，努塞尔特数分别下降了 4.50%和 25.88%。
{"title":"Analysis of variable fluidic properties with varying magnetic influence on an unsteady radiated nanofluid flow on the stagnant point region of a spinning sphere: a numerical exploration","authors":"Raju Bag, Prabir Kumar Kundu","doi":"10.1088/1873-7005/ad6a38","DOIUrl":"https://doi.org/10.1088/1873-7005/ad6a38","url":null,"abstract":"The purpose of this article is to invent the impact of inconstant properties of fluids on the nanofluidic stream towards the stagnation area of a revolving sphere. The motion is treated as an unsteady radiated flow with a nonlinear sort of heat radiation. It is presumed to have Brownian motion & thermophoretic impact in our flow model. Additionally, a variable magnetic influence is addressed perpendicularly on the spherical surface. A suitable alteration has been applied to make dimensionless of our prime flow profiles. The translated equations and the limiting restrictions are solved through a numerical approach. The well established method RK4 Shooting technique is utilized here with Maple 2017 software. In the exploration of the consequences of requisite parameters on thermal, concentration, and flow features, numerous schematics are involved. The nature of physical quantities like Nusselt numbers, friction coefficients, and Sherwood numbers is stated in a tabular manner. It is perceived from the outcomes that the fluid velocity towards the <italic toggle=\"yes\">x</italic>-direction is reduced for the variable viscosity parameter, whereas the unsteadiness parameter promotes it. The enhancement of inconstant thermal conductivity brings a positive influence on the thermal profile of fluid. Nusselt number drops against the thermal radiation & variable viscosity with a rates 4.50% and 25.88% correspondingly.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":"9 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2024-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142224233","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2024-08-22DOI: 10.1088/1873-7005/ad6c7b
V Stegmayer, S Görtz, S Akbari, M Oberlack
This paper analyzes the reduction of the infinite Lundgren–Monin–Novikov (LMN) hierarchy of probability density functions (PDFs) in the statistical theory of helically symmetric turbulence. Lundgren’s hierarchy is considered a complete model, i.e. fully describes the joint multi-point statistic of turbulence though at the expense of dealing with an infinite set of integro-differential equations. The LMN hierarchy and its respective side-conditions are transformed to helical coordinates and thus are dimesionally reduced. In the course of development, a number of key questions were solved, namely in particular the transformation of PDFs and sample space velocities into orthonormal coordinate systems. In a validity check it is shown, that the mean momentum equations derived from the helical LMN hierarchy via statistical moment integration are identical to the mean momentum equations derived by direct ensemble averaging the Navier–Stokes equation, in helically symmetric form. Finally, we derive the equation for the characteristic function equivalent to the PDF equation in a helically symmetric frame, which allows to generate arbitrary nth-order statistical moments by simple differentiation.
本文分析了螺旋对称湍流统计理论中概率密度函数（PDF）的无限伦格伦-莫宁-诺维科夫（LMN）层次结构的简化。伦格伦层次结构被认为是一个完整的模型，即完全描述了湍流的多点联合统计，但代价是要处理无限的积分微分方程集。LMN 层次结构及其相应的侧条件被转换为螺旋坐标，从而被二元化。在开发过程中，解决了一些关键问题，特别是将 PDF 和样本空间速度转换到正交坐标系。在有效性检验中，我们发现通过统计矩积分从螺旋 LMN 层次中推导出的平均动量方程与通过直接集合平均纳维-斯托克斯方程推导出的螺旋对称形式的平均动量方程是相同的。最后，我们推导出在螺旋对称框架下等同于 PDF 方程的特征函数方程，通过简单微分即可生成任意 n 阶统计矩。
{"title":"On the Lundgren hierarchy of helically symmetric turbulence","authors":"V Stegmayer, S Görtz, S Akbari, M Oberlack","doi":"10.1088/1873-7005/ad6c7b","DOIUrl":"https://doi.org/10.1088/1873-7005/ad6c7b","url":null,"abstract":"This paper analyzes the reduction of the infinite Lundgren–Monin–Novikov (LMN) hierarchy of probability density functions (PDFs) in the statistical theory of helically symmetric turbulence. Lundgren’s hierarchy is considered a complete model, i.e. fully describes the joint multi-point statistic of turbulence though at the expense of dealing with an infinite set of integro-differential equations. The LMN hierarchy and its respective side-conditions are transformed to helical coordinates and thus are dimesionally reduced. In the course of development, a number of key questions were solved, namely in particular the transformation of PDFs and sample space velocities into orthonormal coordinate systems. In a validity check it is shown, that the mean momentum equations derived from the helical LMN hierarchy via statistical moment integration are identical to the mean momentum equations derived by direct ensemble averaging the Navier–Stokes equation, in helically symmetric form. Finally, we derive the equation for the characteristic function equivalent to the PDF equation in a helically symmetric frame, which allows to generate arbitrary <inline-formula>\u0000<tex-math><?CDATA $n{mathrm{^{th}}}$?></tex-math><mml:math overflow=\"scroll\"><mml:mrow><mml:msup><mml:mi>n</mml:mi><mml:mrow><mml:mi>t</mml:mi><mml:mi>h</mml:mi></mml:mrow></mml:msup></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"fdrad6c7bieqn1.gif\"></inline-graphic></inline-formula>-order statistical moments by simple differentiation.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":"62 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142224234","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2024-07-10DOI: 10.1088/1873-7005/ad5abc
M L Lanahan, S I Abdel-Khalik and M Yoda
Numerical simulations with semi-empirical turbulence models are commonly used to model impinging jets, often used for cooling solid surfaces. In this work, the constants in the k-ω shear stress transport model in ANSYS FLUENT are calibrated to experimental velocity and heat transfer data for a plane turbulent impinging air jet to determine if Kennedy-O’Hagan calibration (Kennedy and O’Hagan 2001 J. R. Stat. Soc. B 63 425–64) can improve predictions of near-surface velocities and surface Nusselt numbers for similar flows. Impinging jets have been proposed to cool the target plates of the divertor in future magnetic fusion energy reactors, where simulations are used to estimate divertor performance. The flat-plate divertor (Wang et al 2009 Fusion Sci. Technol.56 1023–7) uses a plane jet of helium issuing from a B = 0.5 mm slot to cool a surface with radius of curvature of 44B at a distance 4B from the slot. Predictions from the calibrated numerical model are compared with independent experimental data at different flow conditions, as well as surface temperature data for a flat plate divertor test section. The contribution of this work is evaluation of the accuracy of a calibrated turbulence model for modest extrapolations in flow geometry and flow conditions for a plane impinging jet.
半经验湍流模型的数值模拟通常用于模拟通常用于冷却固体表面的冲击气流。在这项工作中，将 ANSYS FLUENT 中 k-ω 剪切应力传输模型中的常数与平面湍流冲击气流的实验速度和传热数据进行校准，以确定肯尼迪-奥哈根校准（Kennedy and O'Hagan 2001 J. R. Stat. Soc. B 63 425-64）是否能改进类似流动的近表面速度和表面努塞尔特数的预测。有人建议用冲击射流来冷却未来磁核聚变能反应堆中分流器的靶板，并用模拟来估计分流器的性能。平板分流器（Wang 等人，2009 年，Fusion Sci. Technol.56 1023-7）使用从 B = 0.5 毫米槽喷出的平面氦气射流来冷却距离槽 4B 处曲率半径为 44B 的表面。经过校准的数值模型的预测结果与不同流动条件下的独立实验数据以及平板分流器试验段的表面温度数据进行了比较。这项工作的贡献在于评估了校准湍流模型的准确性，以适度推断平面冲击射流的流动几何形状和流动条件。
{"title":"Bayesian parameter estimation and evaluation of the K-ω shear stress transport model for plane impinging jets","authors":"M L Lanahan, S I Abdel-Khalik and M Yoda","doi":"10.1088/1873-7005/ad5abc","DOIUrl":"https://doi.org/10.1088/1873-7005/ad5abc","url":null,"abstract":"Numerical simulations with semi-empirical turbulence models are commonly used to model impinging jets, often used for cooling solid surfaces. In this work, the constants in the k-ω shear stress transport model in ANSYS FLUENT are calibrated to experimental velocity and heat transfer data for a plane turbulent impinging air jet to determine if Kennedy-O’Hagan calibration (Kennedy and O’Hagan 2001 J. R. Stat. Soc. B 63 425–64) can improve predictions of near-surface velocities and surface Nusselt numbers for similar flows. Impinging jets have been proposed to cool the target plates of the divertor in future magnetic fusion energy reactors, where simulations are used to estimate divertor performance. The flat-plate divertor (Wang et al 2009 Fusion Sci. Technol.56 1023–7) uses a plane jet of helium issuing from a B = 0.5 mm slot to cool a surface with radius of curvature of 44B at a distance 4B from the slot. Predictions from the calibrated numerical model are compared with independent experimental data at different flow conditions, as well as surface temperature data for a flat plate divertor test section. The contribution of this work is evaluation of the accuracy of a calibrated turbulence model for modest extrapolations in flow geometry and flow conditions for a plane impinging jet.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":"228 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2024-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141588118","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2024-07-09DOI: 10.1088/1873-7005/ad5b18
James Raja S, Lintu Rajan, Venu Anand
Langmuir probes cannot be used to diagnose cold atmospheric plasma jet, because their presence in the high electric field after-glow region modifies the plasma parameters that they are intended to measure. Here, we propose a system to sample the plasma plume from ambient conditions into a low-pressure region, where probe analysis can be accomplished. The effect of such a sampling process on the number density and velocity of the gas has been studied through simulations and using analytical equations. Simulation results regarding the effect of chamber and orifice dimensions on these parameters, have been presented. Based on this study an experimental chamber was fabricated and Langmuir probe analysis of the sampled plasma was done. Continuum flowing plasma theory was applied and the plasma density and electron temperature were estimated to be 1.8 × 1020m−3 and 4.7 eV respectively for the operating condition of 3 W plasma power at 12 kHz.
{"title":"Sampling of plasma plume from atmosphere into vacuum for reliable Langmuir probe diagnostics","authors":"James Raja S, Lintu Rajan, Venu Anand","doi":"10.1088/1873-7005/ad5b18","DOIUrl":"https://doi.org/10.1088/1873-7005/ad5b18","url":null,"abstract":"Langmuir probes cannot be used to diagnose cold atmospheric plasma jet, because their presence in the high electric field after-glow region modifies the plasma parameters that they are intended to measure. Here, we propose a system to sample the plasma plume from ambient conditions into a low-pressure region, where probe analysis can be accomplished. The effect of such a sampling process on the number density and velocity of the gas has been studied through simulations and using analytical equations. Simulation results regarding the effect of chamber and orifice dimensions on these parameters, have been presented. Based on this study an experimental chamber was fabricated and Langmuir probe analysis of the sampled plasma was done. Continuum flowing plasma theory was applied and the plasma density and electron temperature were estimated to be 1.8 × 10<sup>20</sup>m<sup>−3</sup> and 4.7 eV respectively for the operating condition of 3 W plasma power at 12 kHz.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":"60 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141566546","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2024-06-13DOI: 10.1088/1873-7005/ad5169
Sammar Bashir and Muhammad Sajid
This article aims to examine the dynamics of interfacial flow that occurs when a layer of second-grade fluid rotates over another layer of uniformly rotating immiscible couple stress fluid. Fluid models with different densities, pressures, velocities, and viscosities exhibit intriguing flow properties. Under the restriction of parameter , where (angular velocities ratio) and (densities ratio), the occurrence of similarity solutions under coupling and viscoelastic effects across the interface for both cases of co-and-counter rotation is investigated. In contrast to the rotation of upper fluid, the couple stress fluid layer can counter-rotate. An advanced numerical method known as the Keller box is employed to thoroughly analyze the multiple aspects of the flow. The dominance of the couple stress fluid has been observed in shaping the dynamics of interfacial flow, significantly impacting phenomena such as the generation of inward/outward jets, Ekman pumping/suction, and the development of recirculation regions. Lower-layer far-field flow demonstrates transitions, oscillating between inflow and outflow, depending on parameters and . These findings illustrate an interesting interplay between rheological parameters, providing perspectives into the complicated behaviors of immiscible rotating fluids under different characteristics and useful implications for a variety of practical applications.
{"title":"Interfacial dynamics of two immiscible second-grade and couple stress fluids in rotating and counter-rotating scenarios","authors":"Sammar Bashir and Muhammad Sajid","doi":"10.1088/1873-7005/ad5169","DOIUrl":"https://doi.org/10.1088/1873-7005/ad5169","url":null,"abstract":"This article aims to examine the dynamics of interfacial flow that occurs when a layer of second-grade fluid rotates over another layer of uniformly rotating immiscible couple stress fluid. Fluid models with different densities, pressures, velocities, and viscosities exhibit intriguing flow properties. Under the restriction of parameter , where (angular velocities ratio) and (densities ratio), the occurrence of similarity solutions under coupling and viscoelastic effects across the interface for both cases of co-and-counter rotation is investigated. In contrast to the rotation of upper fluid, the couple stress fluid layer can counter-rotate. An advanced numerical method known as the Keller box is employed to thoroughly analyze the multiple aspects of the flow. The dominance of the couple stress fluid has been observed in shaping the dynamics of interfacial flow, significantly impacting phenomena such as the generation of inward/outward jets, Ekman pumping/suction, and the development of recirculation regions. Lower-layer far-field flow demonstrates transitions, oscillating between inflow and outflow, depending on parameters and . These findings illustrate an interesting interplay between rheological parameters, providing perspectives into the complicated behaviors of immiscible rotating fluids under different characteristics and useful implications for a variety of practical applications.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":"111 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2024-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141507007","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Based on the bioinspired wavy leading-edge, the stall characteristics of the NACA0012 airfoil are optimized. In this paper, the semicircle plus line segment is used to obtain the wavy leading edge. The aerodynamic forces of the airfoil are measured by a high-precision balance, and the detailed flow features of the airfoil are obtained by the oil flow tests. Then, combined with numerical simulation, the optimization mechanism is obtained. The operating conditions are as follows: Mach number ranging from 0.4 to 0.8, and angle of attack ranging from −4° to 25°. The results show that in high speed airflows, compared with the basic airfoil, the lift coefficient of the wavy leading-edge airfoil does not decrease sharply with the increase of the angle of attack, and the drag coefficient of the wavy leading-edge airfoil is similar to the basic airfoil; among the three types of airfoils studied, the larger wavy leading-edge feature size has better aerodynamic characteristics; combined with the numerical simulation results, it can be seen that the stall mechanism of airfoils varies at different Mach numbers. The wavy leading-edge generate streamwise vortex. The streamwise vortices increase energy transport in the boundary layer. Therefore, the separation zone moves toward the trailing edge of the airfoil, and the stall characteristics of the airfoil are optimized.
{"title":"Stall characteristics of wavy leading-edge airfoil in subsonic and transonic airflows","authors":"Yongsheng Zhao, Jiang Zhang, Jingang Dong, Junfei Wu and Jian Zhou","doi":"10.1088/1873-7005/ad3e28","DOIUrl":"https://doi.org/10.1088/1873-7005/ad3e28","url":null,"abstract":"Based on the bioinspired wavy leading-edge, the stall characteristics of the NACA0012 airfoil are optimized. In this paper, the semicircle plus line segment is used to obtain the wavy leading edge. The aerodynamic forces of the airfoil are measured by a high-precision balance, and the detailed flow features of the airfoil are obtained by the oil flow tests. Then, combined with numerical simulation, the optimization mechanism is obtained. The operating conditions are as follows: Mach number ranging from 0.4 to 0.8, and angle of attack ranging from −4° to 25°. The results show that in high speed airflows, compared with the basic airfoil, the lift coefficient of the wavy leading-edge airfoil does not decrease sharply with the increase of the angle of attack, and the drag coefficient of the wavy leading-edge airfoil is similar to the basic airfoil; among the three types of airfoils studied, the larger wavy leading-edge feature size has better aerodynamic characteristics; combined with the numerical simulation results, it can be seen that the stall mechanism of airfoils varies at different Mach numbers. The wavy leading-edge generate streamwise vortex. The streamwise vortices increase energy transport in the boundary layer. Therefore, the separation zone moves toward the trailing edge of the airfoil, and the stall characteristics of the airfoil are optimized.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":"29 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2024-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140887128","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2024-03-05DOI: 10.1088/1873-7005/ad2b74
Jianda Huang, Honglei Bai
Turbulent boundary layer (TBL) flows over various spanwise-heterogeneous rough walls exhibit spanwise variations in turbulence statistics, implying modifications of the turbulent/non-turbulent interface (T/NTI). In this work, based on the datasets of TBL flows over a spanwise-alternating converging/diverging riblets wall, we investigate behavior of T/NTI, properties of ‘bubble’ and ‘drop’ that are associated with T/NTI, as well as connections between T/NTI and large-scale structures within the boundary layer. The flow datasets were obtained through stereoscopic particle image velocimetry measurements on the cross-stream plane of the TBL flow at a Reynolds number Reθ = 1.3 × 104. The T/NTI and associated ‘bubble’ and ‘drop’ are identified using a kinetic energy criterion, while the large-scale structures by a streak detection algorithm. It is observed that the T/NTI height and the occurrence of ‘bubble’ and ‘drop’ display a spanwise-heterogeneous feature, with lower T/NTI height and higher occurrence probability of ‘bubble’ over the diverging section of riblets than over the converging section of riblets. Results of conditional average show that the ‘bubble’ is associated with positive streamwise fluctuations, common-down flow and a pair of counter-rotating streamwise vortices, while the ‘drop’ with negative streamwise fluctuation, common-up flow and a pair of counter-rotating streamwise vortices. Probability density functions of the ‘bubble’ size and fractal dimensions of the T/NTI are found similar for both the riblets and smooth wall flows. Furthermore, it is observed that the large-scale low-speed structures occurring preferentially over the converging section of riblets play a role in elevating T/NTI while the large-scale high-speed ones over the diverging section of riblets lowering down T/NTI.
{"title":"Turbulent/non-turbulent interface of the turbulent boundary-layer over a spanwise-heterogeneous converging/diverging riblets rough wall","authors":"Jianda Huang, Honglei Bai","doi":"10.1088/1873-7005/ad2b74","DOIUrl":"https://doi.org/10.1088/1873-7005/ad2b74","url":null,"abstract":"Turbulent boundary layer (TBL) flows over various spanwise-heterogeneous rough walls exhibit spanwise variations in turbulence statistics, implying modifications of the turbulent/non-turbulent interface (T/NTI). In this work, based on the datasets of TBL flows over a spanwise-alternating converging/diverging riblets wall, we investigate behavior of T/NTI, properties of ‘bubble’ and ‘drop’ that are associated with T/NTI, as well as connections between T/NTI and large-scale structures within the boundary layer. The flow datasets were obtained through stereoscopic particle image velocimetry measurements on the cross-stream plane of the TBL flow at a Reynolds number <inline-formula>\u0000<tex-math><?CDATA $R{e_theta }$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mi>R</mml:mi><mml:mrow><mml:msub><mml:mi>e</mml:mi><mml:mi>θ</mml:mi></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"fdrad2b74ieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> = 1.3 × 10<sup>4</sup>. The T/NTI and associated ‘bubble’ and ‘drop’ are identified using a kinetic energy criterion, while the large-scale structures by a streak detection algorithm. It is observed that the T/NTI height and the occurrence of ‘bubble’ and ‘drop’ display a spanwise-heterogeneous feature, with lower T/NTI height and higher occurrence probability of ‘bubble’ over the diverging section of riblets than over the converging section of riblets. Results of conditional average show that the ‘bubble’ is associated with positive streamwise fluctuations, common-down flow and a pair of counter-rotating streamwise vortices, while the ‘drop’ with negative streamwise fluctuation, common-up flow and a pair of counter-rotating streamwise vortices. Probability density functions of the ‘bubble’ size and fractal dimensions of the T/NTI are found similar for both the riblets and smooth wall flows. Furthermore, it is observed that the large-scale low-speed structures occurring preferentially over the converging section of riblets play a role in elevating T/NTI while the large-scale high-speed ones over the diverging section of riblets lowering down T/NTI.","PeriodicalId":56311,"journal":{"name":"Fluid Dynamics Research","volume":"47 1","pages":""},"PeriodicalIF":1.5,"publicationDate":"2024-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140315683","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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