International Journal of Heat and Fluid Flow最新文献_第8页

Near wake coherent structures of a turbulent axisymmetric bluff body wake

IF 2.6 3区工程技术 Q2 ENGINEERING, MECHANICAL

International Journal of Heat and Fluid Flow

Pub Date : 2024-12-11 DOI: 10.1016/j.ijheatfluidflow.2024.109668

Taihang Zhu, Georgios Rigas, Jonathan F. Morrison

The coherent structures of a turbulent axisymmetric bluff body wake are investigated based on synchronised near-wake velocity and base pressure measurements. The proper orthogonal decomposition (POD) analysis confirms the persistence of the laminar spatio-temporal symmetry breaking instabilities at high Reynolds numbers (here

R e_{D} = 1.88 \times 1 0^{5}

). The laminar rotational symmetry breaking mode randomly meanders in the azimuthal direction, and the unsteady laminar unstable eigenmodes manifest as asymmetric unsteady vortex shedding. Additionally, a coherent streamwise wake pulsation is identified (bubble pumping). Based on the symmetry-breaking property of the turbulent wake, the vector field

q

is decomposed into two antisymmetric components

q^{+}

and

q^{-}

to perform conditional POD (CPOD) with a comparison of

{q^{'}}^{+}

and

q^{+'}

, extracting antisymmetric modes in the stable asymmetric wake states. The asymmetry of the wake due to rotational symmetry break, quantified using the centre of pressure (CoP), is correlated to the base pressure using conditional averaging. The most probable symmetry-breaking wake state corresponds to a low-pressure (high drag) region, and two high-pressure (low drag) regions at the limit of axisymmetric (CoP

\to 0

) and highly asymmetric (CoP

\to \infty

) wake states are identified. The high-pressure wake state in the highly asymmetric wake is caused by the backflow, which results in a high-pressure region near the base edge. Conditional averaging based on the base pressure shows that the transition between high- and low-pressure conditions is coupled with wake asymmetry.

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引用次数: 0

Aspect-ratio effect on the wake of a wall-mounted square cylinder immersed in a turbulent boundary layer

IF 2.6 3区工程技术 Q2 ENGINEERING, MECHANICAL

International Journal of Heat and Fluid Flow

Pub Date : 2024-12-10 DOI: 10.1016/j.ijheatfluidflow.2024.109672

Gerardo Zampino , Marco Atzori , Elias Zea , Evelyn Otero , Ricardo Vinuesa

The wake topology behind a wall-mounted square cylinder immersed in a turbulent boundary layer is investigated using high-resolution large-eddy simulations (LES). The boundary-layer thickness at the obstacle location is fixed, with a Reynolds number based on cylinder height

h

and free-stream velocity

u_{\infty}

of 10,000 while the aspect ratio (AR), defined as obstacle height divided by its width, ranges from 1 to 4. The mesh resolution is comparable to DNS standards used for similar wall-mounted obstacles, though with relatively lower Reynolds numbers. The effects of AR on wake structures, turbulence production, and transport are analyzed via Reynolds stresses, anisotropy-invariant maps (AIM), and the turbulent kinetic energy (TKE) budget. In particular, the transition from “dipole” to a “quadrupole” wake is extensively examined as AR increases. With increasing AR, the wake shrinks in both the streamwise and spanwise directions, attributed to the occurrence of the base vortices (

AR = 3

and 4). This change in the flow structure also affects the size of the positive-production region that extends from the roof and the flank of the obstacle to the wake core. The AIMs confirm three-dimensional wake features, showing TKE redistribution in all directions (Simonsen and Krogstad, 2005). Stronger turbulence production in

AR = 3

and 4 cases highlights the role of tip and base vortices behind the cylinder. The overall aim is to refine the dipole-to-quadrupole transition as a function of AR and accounting for the incoming TBL properties. The novelty relies on proposing the momentum-thickness-based Reynolds number

{Re}_{θ}

as a discriminant for assessing TBL effects on turbulent wake structures.

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引用次数: 0

Impact of blade twisting and tip clearance on centrifugal pump performance under air–water two-phase flow

IF 2.6 3区工程技术 Q2 ENGINEERING, MECHANICAL

International Journal of Heat and Fluid Flow

Pub Date : 2024-12-10 DOI: 10.1016/j.ijheatfluidflow.2024.109682

Michael Mansour , Dominique Thévenin

The performance characteristics of a centrifugal pump were investigated experimentally for different conditions of air–water two-phase flow. A 3D semi-open impeller (with twisted blades) and a geometrically similar 2D semi-open impeller (with straight elliptical blades) were employed to compare the pump behavior using each of them, revealing the influence of the blade twisting. Additionally, the effect of the tip clearance gap on the performance of each impeller was investigated by employing either a standard or an increased gap. A rotational speed of 1450 rpm was set for all experiments. The performance of the pump was reported and described for either a constant gas volume fraction or a constant air flow rate at the pump inlet. Possible hysteresis effects were studied by approaching the desired operating conditions using different procedures. The head degradation behavior, the pump surging conditions, and the flow instabilities were considered as well. The two-phase flow regimes were recorded and identified for all the considered cases using a high-speed recording system. The results show that for single-phase flow, both impellers perform similarly, with the 3D impeller showing slight advantages at part-load and the 2D impeller excelling at near-optimal and overload conditions. For two-phase flows with high gas volume fractions, the 3D impeller maintains better performance at overload, while the 2D impeller performs better at part-load conditions. Increasing the gap slightly improves performance for gas volume fractions between 5% and 7% in both impellers. Additionally, the 2D impeller demonstrates a stronger ability to suppress and delay surging and flow instabilities compared to the 3D impeller, making it preferable for applications requiring stable operation across a range of gas volume fractions and load conditions.

{"title":"Impact of blade twisting and tip clearance on centrifugal pump performance under air–water two-phase flow","authors":"Michael Mansour , Dominique Thévenin","doi":"10.1016/j.ijheatfluidflow.2024.109682","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109682","url":null,"abstract":"<div><div>The performance characteristics of a centrifugal pump were investigated experimentally for different conditions of air–water two-phase flow. A 3D semi-open impeller (with twisted blades) and a geometrically similar 2D semi-open impeller (with straight elliptical blades) were employed to compare the pump behavior using each of them, revealing the influence of the blade twisting. Additionally, the effect of the tip clearance gap on the performance of each impeller was investigated by employing either a standard or an increased gap. A rotational speed of 1450 rpm was set for all experiments. The performance of the pump was reported and described for either a constant gas volume fraction or a constant air flow rate at the pump inlet. Possible hysteresis effects were studied by approaching the desired operating conditions using different procedures. The head degradation behavior, the pump surging conditions, and the flow instabilities were considered as well. The two-phase flow regimes were recorded and identified for all the considered cases using a high-speed recording system. The results show that for single-phase flow, both impellers perform similarly, with the 3D impeller showing slight advantages at part-load and the 2D impeller excelling at near-optimal and overload conditions. For two-phase flows with high gas volume fractions, the 3D impeller maintains better performance at overload, while the 2D impeller performs better at part-load conditions. Increasing the gap slightly improves performance for gas volume fractions between 5% and 7% in both impellers. Additionally, the 2D impeller demonstrates a stronger ability to suppress and delay surging and flow instabilities compared to the 3D impeller, making it preferable for applications requiring stable operation across a range of gas volume fractions and load conditions.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109682"},"PeriodicalIF":2.6,"publicationDate":"2024-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140143","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}

引用次数: 0

Transition model based on the laminar kinetic energy concept for the prediction of all transition modes

IF 2.6 3区工程技术 Q2 ENGINEERING, MECHANICAL

International Journal of Heat and Fluid Flow

Pub Date : 2024-12-10 DOI: 10.1016/j.ijheatfluidflow.2024.109680

M. Dellacasagrande , A. Ghidoni , G. Noventa , D. Simoni

Separation-induced transition showed to be the weakness of the transition models based on the laminar kinetic energy concept. In fact, these models contemplate only the Tolmien–Schlichting waves, for the natural mode, and the Klebanoff streaks, for the bypass mode. Literature is very poor about the use of these models to cases with the separation-induced mode and in all these works no proofs of the phenomenological agreement between the models and the physics of the flow are spotlighted. A further improvement for the Reynolds-Averaged Navier–Stokes equations in separated and transitional shear layers needs more accurate models to describe the physics behind the phenomena, e.g., the introduction of ad-hoc designed terms for the Kelvin–Helmholtz instability in the transport equations. The objective of this work is to assess a phenomenological and local transition model based on the laminar kinetic energy concept, implemented in a high-order discontinuous Galerkin solver, for the simulation of transitional flows. The prediction capabilities of the model are proved with the simulations of the flow over the ERCOFTAC and UNIGE flat plates, characterized by the bypass and separation-induced mode of transition. The education of the model is not only based on integral coefficients and first-order statistics, but also on the turbulence intensity, laminar and turbulent kinetic energy distributions extracted from finely processed experimental data.

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引用次数: 0

Investigation of the heat transfer performance of two-phase flow in a novel step-by-step distributed heat exchanger

IF 2.6 3区工程技术 Q2 ENGINEERING, MECHANICAL

International Journal of Heat and Fluid Flow

Pub Date : 2024-12-09 DOI: 10.1016/j.ijheatfluidflow.2024.109687

Shuang-gen Yang , Huan-ling Liu

With the miniaturization of electronic chips, and the complexity and diversity of functions, the application of multiple heat source arrays has appeared in recent years. In order to improve the heat dissipation performance of multiple high heat flux chips, this work innovatively designs a step-by-step distributed heat exchanger (SSD), which uses ethanol as coolant and is used for two-phase flow heat dissipation. Then, in order to improve the cooling ability, a crossed step-by-step distributed heat exchanger (CSSD) is proposed by arranging cross flow channels with high heat flux. The VOF two-phase flow numerical method is used to simulate the performance of these two kinds of heat exchangers. In addition, the effects of gravity and inlet height on the performance of the heat CSSD exchanger are studied. The results show that CSSD can shorten the bubble generation time, increases the gas volume fraction in the channel, increase the gas disturbance, and intensify the heat dissipation of two-phase flow compared to the SSD design. The results show that CSSD can reduce the maximum temperature of the heat exchanger and improve the temperature uniformity. Gravity has little effect on two-phase flow heat transfer. In addition, we set up a two-phase flow experimental system to verify the correctness of the numerical simulation. The results indicates that the numerical results are consistent with the experimental results.

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引用次数: 0

Additive-feature-attribution methods: A review on explainable artificial intelligence for fluid dynamics and heat transfer

IF 2.6 3区工程技术 Q2 ENGINEERING, MECHANICAL

International Journal of Heat and Fluid Flow

Pub Date : 2024-12-09 DOI: 10.1016/j.ijheatfluidflow.2024.109662

Andrés Cremades , Sergio Hoyas , Ricardo Vinuesa

The use of data-driven methods in fluid mechanics has surged dramatically in recent years due to their capacity to adapt to the complex and multi-scale nature of turbulent flows, as well as to detect patterns in large-scale simulations or experimental tests. In order to interpret the relationships generated in the models during the training process, numerical attributions need to be assigned to the input features. One important example are the additive-feature-attribution methods. These explainability methods link the input features with the model prediction, providing an interpretation based on a linear formulation of the models. The Shapley additive explanations (SHAP values) are formulated as the only possible interpretation that offers a unique solution for understanding the model. In this manuscript, the additive-feature-attribution methods are presented, showing four common implementations in the literature: kernel SHAP, tree SHAP, gradient SHAP, and deep SHAP. Then, the main applications of the additive-feature-attribution methods are introduced, dividing them into three main groups: turbulence modeling, fluid-mechanics fundamentals, and applied problems in fluid dynamics and heat transfer. This review shows that explainability techniques, and in particular additive-feature-attribution methods, are crucial for implementing interpretable and physics-compliant deep-learning models in the fluid-mechanics field.

{"title":"Additive-feature-attribution methods: A review on explainable artificial intelligence for fluid dynamics and heat transfer","authors":"Andrés Cremades , Sergio Hoyas , Ricardo Vinuesa","doi":"10.1016/j.ijheatfluidflow.2024.109662","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109662","url":null,"abstract":"<div><div>The use of data-driven methods in fluid mechanics has surged dramatically in recent years due to their capacity to adapt to the complex and multi-scale nature of turbulent flows, as well as to detect patterns in large-scale simulations or experimental tests. In order to interpret the relationships generated in the models during the training process, numerical attributions need to be assigned to the input features. One important example are the additive-feature-attribution methods. These explainability methods link the input features with the model prediction, providing an interpretation based on a linear formulation of the models. The Shapley additive explanations (SHAP values) are formulated as the only possible interpretation that offers a unique solution for understanding the model. In this manuscript, the additive-feature-attribution methods are presented, showing four common implementations in the literature: kernel SHAP, tree SHAP, gradient SHAP, and deep SHAP. Then, the main applications of the additive-feature-attribution methods are introduced, dividing them into three main groups: turbulence modeling, fluid-mechanics fundamentals, and applied problems in fluid dynamics and heat transfer. This review shows that explainability techniques, and in particular additive-feature-attribution methods, are crucial for implementing interpretable and physics-compliant deep-learning models in the fluid-mechanics field.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109662"},"PeriodicalIF":2.6,"publicationDate":"2024-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140624","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}

引用次数: 0

Effects of cooling hole blockage on heat transfer and film cooling effectiveness of gas turbine squealer tip

IF 2.6 3区工程技术 Q2 ENGINEERING, MECHANICAL

International Journal of Heat and Fluid Flow

Pub Date : 2024-12-07 DOI: 10.1016/j.ijheatfluidflow.2024.109678

Kewen Xu , Kun He , Xin Yan

The complex flow fields in the squealer tip region are conducive to the particle deposition and cooling hole blockage of gas turbine blades. The blockage of film cooling hole causes the elevation of heat load and reduction of film cooling effect in the squealer tip gap. In this paper, influences of cooling hole blockage on the film cooling effectiveness and heat transfer on the squealer tip are investigated by means of numerical methods. To describe the degree of hole blockage, the blockage ratio B and the blockage angle β are introduced for the film cooled squealer tip with cooling hole blockage. The film cooling effectiveness and heat transfer coefficient on the squealer tip are obtained at the three blowing ratios (M = 0.5, 1.0, and 2.0), three blockage ratios (B = 0.2, 0.4, and 0.8), and three blockage angles (β = 20°, 30°, and 40°). The results show that the film cooling effectiveness and heat transfer on the squealer tip is highly dependent on the blockage ratio, but not sensitive to the variation of blockage angle. The cooling hole blockage has a profound effect on the coolant ejection velocity and angle. At M = 0.5 and 1.0, the film cooling effectiveness is reduced by 32.11 % and 39.40 % respectively for the blocked case with B = 0.6 and β = 40° compared to the design case (i.e. no blockage), whereas the averaged heat transfer coefficient on the cavity floor for the blocked case with B = 0.6 and β = 20° is increased by 9.77 % and 12.57 % respectively compared to the design case. The effect of cooling hole blockage on the heat transfer coefficient of the squealer tip exhibits irregular characteristic at M = 2.0. The highest heat load is observed on the squealer tip at B = 0.4 and β = 40°, and the lowest film cooling effectiveness is observed at B = 0.4, β = 30°. In these cases, the averaged film cooling effectiveness is decreased by 25.49 % compared to the design cases, and the averaged heat transfer coefficient on the cavity floor is increased by 14.6 %.

{"title":"Effects of cooling hole blockage on heat transfer and film cooling effectiveness of gas turbine squealer tip","authors":"Kewen Xu , Kun He , Xin Yan","doi":"10.1016/j.ijheatfluidflow.2024.109678","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109678","url":null,"abstract":"<div><div>The complex flow fields in the squealer tip region are conducive to the particle deposition and cooling hole blockage of gas turbine blades. The blockage of film cooling hole causes the elevation of heat load and reduction of film cooling effect in the squealer tip gap. In this paper, influences of cooling hole blockage on the film cooling effectiveness and heat transfer on the squealer tip are investigated by means of numerical methods. To describe the degree of hole blockage, the blockage ratio <em>B</em> and the blockage angle <em>β</em> are introduced for the film cooled squealer tip with cooling hole blockage. The film cooling effectiveness and heat transfer coefficient on the squealer tip are obtained at the three blowing ratios (<em>M</em> = 0.5, 1.0, and 2.0), three blockage ratios (<em>B</em> = 0.2, 0.4, and 0.8), and three blockage angles (<em>β</em> = 20°, 30°, and 40°). The results show that the film cooling effectiveness and heat transfer on the squealer tip is highly dependent on the blockage ratio, but not sensitive to the variation of blockage angle. The cooling hole blockage has a profound effect on the coolant ejection velocity and angle. At <em>M</em> = 0.5 and 1.0, the film cooling effectiveness is reduced by 32.11 % and 39.40 % respectively for the blocked case with <em>B</em> = 0.6 and <em>β</em> = 40° compared to the design case (i.e. no blockage), whereas the averaged heat transfer coefficient on the cavity floor for the blocked case with <em>B</em> = 0.6 and <em>β</em> = 20° is increased by 9.77 % and 12.57 % respectively compared to the design case. The effect of cooling hole blockage on the heat transfer coefficient of the squealer tip exhibits irregular characteristic at <em>M</em> = 2.0. The highest heat load is observed on the squealer tip at <em>B</em> = 0.4 and <em>β</em> = 40°, and the lowest film cooling effectiveness is observed at <em>B</em> = 0.4, <em>β</em> = 30°. In these cases, the averaged film cooling effectiveness is decreased by 25.49 % compared to the design cases, and the averaged heat transfer coefficient on the cavity floor is increased by 14.6 %.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109678"},"PeriodicalIF":2.6,"publicationDate":"2024-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140141","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}

引用次数: 0

Flow mechanism across 180° sharp bend of matrix-cooled serpentine channel

IF 2.6 3区工程技术 Q2 ENGINEERING, MECHANICAL

International Journal of Heat and Fluid Flow

Pub Date : 2024-12-07 DOI: 10.1016/j.ijheatfluidflow.2024.109683

Nishab Ali, Arun Chand, Vaibhav Sharma, Andallib Tariq

Vortex merging and evolution mechanisms have been characterized across the 180° sharp bend region of matrix-cooled serpentine channel with the help of stereo Particle Image Velocimetry (PIV) system. Complete evolution of flow phenomenon is captured through measurements in multiple vertical and horizontal planes, and the mechanism responsible for evolution of vortices at a typical Reynolds number (Re) of 6500 has been explored. It was observed that the matrix subchannel typically produces a kind of swirling pattern downstream of the matrix structure, which is similar to the swirling flow occurring in various other application areas. Two co-rotating vortices emanate out of matrix subchannels (observed in secondary plane), which immediately merge into a single vortex at the onset of the bend and propagate further downstream of the bend section, where a pair of side-by-side counter-rotating vortices are observed later. Numerical simulations have also been performed to get the pressure distribution and flow characteristics within oblique/inclined planes along the bend, which are difficult to obtain experimentally through PIV. Results demonstrate that the vortical structures lose their strength during merging and turning, significantly reducing turbulence while passing through the bend. Based on the combination of experimental and numerical observations, a conceptual diagram depicting flow dynamics has been proposed, which provides the overall perspective of vortices evolution and merging across the bend.

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引用次数: 0

Higher-order turbulent statistics of submerged wall jet over hemispherical macro-rough boundary: Insights from third-order moments, turbulent kinetic energy and length scales

IF 2.6 3区工程技术 Q2 ENGINEERING, MECHANICAL

International Journal of Heat and Fluid Flow

Pub Date : 2024-12-07 DOI: 10.1016/j.ijheatfluidflow.2024.109676

Sammelan Chowdhury

This study investigates, for the first time, turbulence in a submerged wall jet over a macro-rough boundary, emphasizing third-order moments, turbulent kinetic energy (TKE) field and budget, and the evolution of turbulent length scales using the instantaneous velocity data captured by Acoustic Doppler Velocimeter or Vectrino. Negative third-order moments in the jet outer layer and inner circulatory flow layer indicate downward and upstream fluxes of Reynolds normal stresses with deceleration. In the jet inner and reverse flow layers, positive values represent upward and downstream fluxes with substantial acceleration, reflecting inward and outward interaction events. Time-averaged TKE field indicates significant fluctuations in all three velocity components near the macro-rough boundary and along the null streamwise velocity line. Near-bed TKE production is higher, decreasing to the edge of jet inner layer, then peaks at maximum Reynolds shear stress. TKE dissipation steeply increases from the boundary, decreasing after the null-point of Reynolds shear stress. Variation of Taylor microscale and Kolmogorov length scale reveals that the Kolmogorov length scale follows similar trends but with smaller magnitudes, ranging from 0.0075 to 0.05 times the Taylor microscale.

{"title":"Higher-order turbulent statistics of submerged wall jet over hemispherical macro-rough boundary: Insights from third-order moments, turbulent kinetic energy and length scales","authors":"Sammelan Chowdhury","doi":"10.1016/j.ijheatfluidflow.2024.109676","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109676","url":null,"abstract":"<div><div>This study investigates, for the first time, turbulence in a submerged wall jet over a macro-rough boundary, emphasizing third-order moments, turbulent kinetic energy (TKE) field and budget, and the evolution of turbulent length scales using the instantaneous velocity data captured by Acoustic Doppler Velocimeter or <em>Vectrino</em>. Negative third-order moments in the jet outer layer and inner circulatory flow layer indicate downward and upstream fluxes of Reynolds normal stresses with deceleration. In the jet inner and reverse flow layers, positive values represent upward and downstream fluxes with substantial acceleration, reflecting inward and outward interaction events. Time-averaged TKE field indicates significant fluctuations in all three velocity components near the macro-rough boundary and along the null streamwise velocity line. Near-bed TKE production is higher, decreasing to the edge of jet inner layer, then peaks at maximum Reynolds shear stress. TKE dissipation steeply increases from the boundary, decreasing after the null-point of Reynolds shear stress. Variation of Taylor microscale and Kolmogorov length scale reveals that the Kolmogorov length scale follows similar trends but with smaller magnitudes, ranging from 0.0075 to 0.05 times the Taylor microscale.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109676"},"PeriodicalIF":2.6,"publicationDate":"2024-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140129","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}

引用次数: 0

Coaxial round water jet at velocity ratios close to unity, Part I: Mean and turbulent flow characteristics

IF 2.6 3区工程技术 Q2 ENGINEERING, MECHANICAL

International Journal of Heat and Fluid Flow

Pub Date : 2024-12-07 DOI: 10.1016/j.ijheatfluidflow.2024.109650

D. Hasin , A. Mitra , R. van Hout

In this paper, planar time-resolved particle image velocimetry measurements are reported in the near-field of a coaxial jet at velocity ratios,

r_{u}

= 0.66, 1.0 and 1.32. At each

r_{u}

, at least two different Reynolds numbers, Re, were investigated. Spatial distributions of mean velocities, Reynolds stresses, vorticity and swirling strength strongly depend on

r_{u}

. Re effects in the normalized, mean velocity distributions were mainly visible in the wake associated with the finite lip thickness. In addition, increased normalized Reynolds stresses were obtained at

x / D_{o} \approx

1.5 for the lowest Re at a given

r_{u}

. Farther downstream, Re effects became negligible as inner and outer jets merged. A comparison between different terms in the turbulent kinetic energy (TKE) budget showed that TKE is predominantly produced in the outer shear layer, while turbulent diffusion results in radial transport. Mean advection of TKE (a “sink” term) is mainly significant close to the nozzle exit.

{"title":"Coaxial round water jet at velocity ratios close to unity, Part I: Mean and turbulent flow characteristics","authors":"D. Hasin , A. Mitra , R. van Hout","doi":"10.1016/j.ijheatfluidflow.2024.109650","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109650","url":null,"abstract":"<div><div>In this paper, planar time-resolved particle image velocimetry measurements are reported in the near-field of a coaxial jet at velocity ratios, <span><math><msub><mrow><mi>r</mi></mrow><mrow><mi>u</mi></mrow></msub></math></span> = 0.66, 1.0 and 1.32. At each <span><math><msub><mrow><mi>r</mi></mrow><mrow><mi>u</mi></mrow></msub></math></span>, at least two different Reynolds numbers, Re, were investigated. Spatial distributions of mean velocities, Reynolds stresses, vorticity and swirling strength strongly depend on <span><math><msub><mrow><mi>r</mi></mrow><mrow><mi>u</mi></mrow></msub></math></span>. Re effects in the normalized, mean velocity distributions were mainly visible in the wake associated with the finite lip thickness. In addition, increased normalized Reynolds stresses were obtained at <span><math><mrow><mi>x</mi><mo>/</mo><msub><mrow><mi>D</mi></mrow><mrow><mi>o</mi></mrow></msub><mo>≈</mo></mrow></math></span> 1.5 for the lowest Re at a given <span><math><msub><mrow><mi>r</mi></mrow><mrow><mi>u</mi></mrow></msub></math></span>. Farther downstream, Re effects became negligible as inner and outer jets merged. A comparison between different terms in the turbulent kinetic energy (TKE) budget showed that TKE is predominantly produced in the outer shear layer, while turbulent diffusion results in radial transport. Mean advection of TKE (a “sink” term) is mainly significant close to the nozzle exit.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109650"},"PeriodicalIF":2.6,"publicationDate":"2024-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140134","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}

引用次数: 0