Pub Date : 2022-05-24DOI: 10.1080/14685248.2022.2071429
Ziye Fan, Z. Tang, Xingyu Ma, N. Jiang
Experiments of particle image velocimetry (PIV) in the turbulent boundary layer at have been conducted to investigate the convection characteristic of turbulent structure and the validity of Taylor’s hypothesis. Views of ( , the boundary layer thickness) were captured by four streamwise-arranged cameras. Distributions of streamwise turbulent kinetic energy on a streamwise scale were investigated by continuous-wave transform, and scales were found where the portion of streamwise turbulent kinetic energy approaches maximum. Fluctuating velocities (instant velocity minus average velocity on time dimension) were divided into large-scale motion (LSM) and small-scale motion (SSM) portions, bounded by . Convection velocities of LSM and SSM are determined by the spatiotemporal correlation method, and they are larger than local average velocities in near-wall regions, but smaller than local average velocities in wake regions. Statistical characteristics between velocity fields reconstructed by Taylor’s hypothesis and original fields were compared by the autocorrelation method, and the reconstructed field’s patterns are longer than original field’s patterns, while their heights do not have clear distinction. The correlation of original velocity fields and reconstructed fields shows that LSM can hold on over and SSM over in streamwise convection separation for regions of , given a threshold value (correlation coefficient C = 0.6).
{"title":"Convection of multi-scale motions in turbulent boundary layer by temporal resolution particle image velocimetry","authors":"Ziye Fan, Z. Tang, Xingyu Ma, N. Jiang","doi":"10.1080/14685248.2022.2071429","DOIUrl":"https://doi.org/10.1080/14685248.2022.2071429","url":null,"abstract":"Experiments of particle image velocimetry (PIV) in the turbulent boundary layer at have been conducted to investigate the convection characteristic of turbulent structure and the validity of Taylor’s hypothesis. Views of ( , the boundary layer thickness) were captured by four streamwise-arranged cameras. Distributions of streamwise turbulent kinetic energy on a streamwise scale were investigated by continuous-wave transform, and scales were found where the portion of streamwise turbulent kinetic energy approaches maximum. Fluctuating velocities (instant velocity minus average velocity on time dimension) were divided into large-scale motion (LSM) and small-scale motion (SSM) portions, bounded by . Convection velocities of LSM and SSM are determined by the spatiotemporal correlation method, and they are larger than local average velocities in near-wall regions, but smaller than local average velocities in wake regions. Statistical characteristics between velocity fields reconstructed by Taylor’s hypothesis and original fields were compared by the autocorrelation method, and the reconstructed field’s patterns are longer than original field’s patterns, while their heights do not have clear distinction. The correlation of original velocity fields and reconstructed fields shows that LSM can hold on over and SSM over in streamwise convection separation for regions of , given a threshold value (correlation coefficient C = 0.6).","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45733741","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 : 2022-05-06DOI: 10.1080/14685248.2022.2070174
Sarvesh Kumar, Amitesh Kumar
In this paper, the three-dimensional turbulent wall jet flow is investigated for three different developing initial velocity profiles. The developing initial velocity profiles at the nozzle exit are generated by three different lengths ( , 50 and 90) of the square nozzle . The velocity profiles at the nozzle exit are measured with the single probe hot-wire anemometer. The Reynolds number based on the bulk mean velocity and nozzle height is 25,000 for all the cases. The measured velocity profiles at the nozzle exit are used as the inlet conditions for the numerical simulations. The results show that the initial velocity profile affects the flow field of the wall jet in near and far-field regions. It is found that the contours of streamwise velocity and turbulent kinetic energy exhibit the effect of initial conditions in the near field. The Reynolds shear stress component dominates in the vertical jet centreline plane, and it increases with a decrease in the nozzle length. The Reynolds shear stress component dominates in the lateral plane, and also exhibit the dependency on initial conditions.
{"title":"Dependence of wall jet phenomenology on inlet conditions and near-field flow development","authors":"Sarvesh Kumar, Amitesh Kumar","doi":"10.1080/14685248.2022.2070174","DOIUrl":"https://doi.org/10.1080/14685248.2022.2070174","url":null,"abstract":"In this paper, the three-dimensional turbulent wall jet flow is investigated for three different developing initial velocity profiles. The developing initial velocity profiles at the nozzle exit are generated by three different lengths ( , 50 and 90) of the square nozzle . The velocity profiles at the nozzle exit are measured with the single probe hot-wire anemometer. The Reynolds number based on the bulk mean velocity and nozzle height is 25,000 for all the cases. The measured velocity profiles at the nozzle exit are used as the inlet conditions for the numerical simulations. The results show that the initial velocity profile affects the flow field of the wall jet in near and far-field regions. It is found that the contours of streamwise velocity and turbulent kinetic energy exhibit the effect of initial conditions in the near field. The Reynolds shear stress component dominates in the vertical jet centreline plane, and it increases with a decrease in the nozzle length. The Reynolds shear stress component dominates in the lateral plane, and also exhibit the dependency on initial conditions.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43182181","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 : 2022-04-01DOI: 10.1080/14685248.2022.2051531
G. K. Balajee, N. Panchapakesan
We present results from three large eddy simulations (LES). The first two were those of a single jet at a Reynolds number of 11000 with different cell density distributions. The simulation results are validated with earlier experimental and computational studies at the same Reynolds number and almost the same boundary conditions. We establish the repeatability and reproducibility of the characterisation of a single axisymmetric jet. Additionally, we performed an LES of five round jets using the same discretisation schemes and boundary conditions. The five jets were placed in a cross or plus configuration, with a central jet surrounded by four outer jets. The mass flux, momentum flux and the Reynolds number of the five jet configuration were set to be equal to those of the single jet. Further, we analyse the near-field development of the multiple jets, along with entrainment and symmetry characteristics as the jet evolves. LES's ability to provide information about large-scale motions was used to compute conditional statistics. We, then, present details of an initial attempt to characterise the turbulent non-turbulent interface boundary and the coherent structures in the core of the jet in a unified manner using helicity density as the detector variable.
{"title":"Large eddy simulations of single and multiple turbulent round jets","authors":"G. K. Balajee, N. Panchapakesan","doi":"10.1080/14685248.2022.2051531","DOIUrl":"https://doi.org/10.1080/14685248.2022.2051531","url":null,"abstract":"We present results from three large eddy simulations (LES). The first two were those of a single jet at a Reynolds number of 11000 with different cell density distributions. The simulation results are validated with earlier experimental and computational studies at the same Reynolds number and almost the same boundary conditions. We establish the repeatability and reproducibility of the characterisation of a single axisymmetric jet. Additionally, we performed an LES of five round jets using the same discretisation schemes and boundary conditions. The five jets were placed in a cross or plus configuration, with a central jet surrounded by four outer jets. The mass flux, momentum flux and the Reynolds number of the five jet configuration were set to be equal to those of the single jet. Further, we analyse the near-field development of the multiple jets, along with entrainment and symmetry characteristics as the jet evolves. LES's ability to provide information about large-scale motions was used to compute conditional statistics. We, then, present details of an initial attempt to characterise the turbulent non-turbulent interface boundary and the coherent structures in the core of the jet in a unified manner using helicity density as the detector variable.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41548644","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 : 2022-03-29DOI: 10.1080/14685248.2022.2053143
L. Thamri, T. Naffouti
In the present investigation, the evolution of homogeneous and stratified turbulence under a horizontal and a vertical shear is deliberate by coupled second-order model SSG-SL. This model is a result of a combination between the Speziale, Sarkar and Gatski model (SSG) and the Shih and Lumley model (SL). Horizontal shear and vertical shear are related to the angle between the shear and the vertical gradient of stratification; θ = π/2 and θ = 0, respectively. This study is performed for different values of Froude number Fr ranging from 0.35–1.11. The SSG-SL model confirms the asymptotic equilibrium states for various physical parameters governing the problem (b12, b11, ε/KS, , K/E and Kρ/E) for two shear orientations (θ = π/2 and θ = 0). A comparison between findings using the present coupled model of SSG-SL and those by Direct Numerical Simulation of Jacobitz (DNSJ) [Jacobitz F, Sarkar S. A direct numerical study of transport and anisotropy in a stably stratified turbulent flow with uniform horizontal shear. Flow Turbul Combust. 2000;63:343–360.; Jacobitz F. A comparison of the turbulence evolution in a stratified fluid with vertical or horizontal shear. J Turbul. 2002;3:1–18.] is carried out. For the horizontal shear related to θ = π/2, an excellent agreement between predictions by the SSG-SL model and the results of DNSJ [Jacobitz, Sarkar;Jacobitz] is detected for turbulent thermal and dynamic fields.
{"title":"Effect of the Froude number on a stratified turbulence under two shear orientations using coupled SSG and SL models","authors":"L. Thamri, T. Naffouti","doi":"10.1080/14685248.2022.2053143","DOIUrl":"https://doi.org/10.1080/14685248.2022.2053143","url":null,"abstract":"In the present investigation, the evolution of homogeneous and stratified turbulence under a horizontal and a vertical shear is deliberate by coupled second-order model SSG-SL. This model is a result of a combination between the Speziale, Sarkar and Gatski model (SSG) and the Shih and Lumley model (SL). Horizontal shear and vertical shear are related to the angle between the shear and the vertical gradient of stratification; θ = π/2 and θ = 0, respectively. This study is performed for different values of Froude number Fr ranging from 0.35–1.11. The SSG-SL model confirms the asymptotic equilibrium states for various physical parameters governing the problem (b12, b11, ε/KS, , K/E and Kρ/E) for two shear orientations (θ = π/2 and θ = 0). A comparison between findings using the present coupled model of SSG-SL and those by Direct Numerical Simulation of Jacobitz (DNSJ) [Jacobitz F, Sarkar S. A direct numerical study of transport and anisotropy in a stably stratified turbulent flow with uniform horizontal shear. Flow Turbul Combust. 2000;63:343–360.; Jacobitz F. A comparison of the turbulence evolution in a stratified fluid with vertical or horizontal shear. J Turbul. 2002;3:1–18.] is carried out. For the horizontal shear related to θ = π/2, an excellent agreement between predictions by the SSG-SL model and the results of DNSJ [Jacobitz, Sarkar;Jacobitz] is detected for turbulent thermal and dynamic fields.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48488718","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 : 2022-03-04DOI: 10.1080/14685248.2022.2046762
T. Ohta, Fumiya Osaka, Yuta Kitagawa
Modulation of turbulent flow by cavitation in fluid machinery can cause vibrations, noise, and erosion. In this study, we confirm the cavitation phenomenon and observe its characteristics to predict the flow and control it accordingly. We perform a direct numerical simulation of the turbulent Couette flow of water with vortex cavitation using a cavitation model to predict phase change based on pressure distribution. In this simulation, we investigate the characteristics of the local interaction between turbulence vortices and cavitation and the global modulation of the turbulent flow, i.e. mean velocity and wall friction coefficient. We observe that a cavity is generated where a low-pressure region is created in the centre of the turbulence vortex; the growth of the cavity weakens the vortex and reduces the intensity of the turbulence. Further, the vortex becomes stronger as the cavity contracts; this phenomenon occurs repeatedly in a turbulent flow field with vortex cavitation. In a turbulent flow field with vortex cavitation, mechanical oscillations can occur spontaneously. In addition, we found that the turbulence vortex weakened by cavitation regenerates around the cavity. The unsteady phenomenon of the turbulence vortex cavitation repeatedly grows and decays monotonically; however, it does not necessarily repeat these spatially in the same manner. The spatial characteristics of the turbulence structure are different from those observed in single-phase turbulent flow.
{"title":"Modulation of turbulent Couette flow with vortex cavitation in a minimal flow unit","authors":"T. Ohta, Fumiya Osaka, Yuta Kitagawa","doi":"10.1080/14685248.2022.2046762","DOIUrl":"https://doi.org/10.1080/14685248.2022.2046762","url":null,"abstract":"Modulation of turbulent flow by cavitation in fluid machinery can cause vibrations, noise, and erosion. In this study, we confirm the cavitation phenomenon and observe its characteristics to predict the flow and control it accordingly. We perform a direct numerical simulation of the turbulent Couette flow of water with vortex cavitation using a cavitation model to predict phase change based on pressure distribution. In this simulation, we investigate the characteristics of the local interaction between turbulence vortices and cavitation and the global modulation of the turbulent flow, i.e. mean velocity and wall friction coefficient. We observe that a cavity is generated where a low-pressure region is created in the centre of the turbulence vortex; the growth of the cavity weakens the vortex and reduces the intensity of the turbulence. Further, the vortex becomes stronger as the cavity contracts; this phenomenon occurs repeatedly in a turbulent flow field with vortex cavitation. In a turbulent flow field with vortex cavitation, mechanical oscillations can occur spontaneously. In addition, we found that the turbulence vortex weakened by cavitation regenerates around the cavity. The unsteady phenomenon of the turbulence vortex cavitation repeatedly grows and decays monotonically; however, it does not necessarily repeat these spatially in the same manner. The spatial characteristics of the turbulence structure are different from those observed in single-phase turbulent flow.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43773089","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 : 2022-03-01DOI: 10.1080/14685248.2022.2037621
Fei Liao
This paper investigates the turbulent flow and aerodynamic noise of a half-cylinder body mounted on a flat plate at using high-order cell-centred finite difference method with delayed detached-eddy simulation (DDES) and large-eddy simulation (LES). Transient flow patterns from the two simulations are found to be very different in consideration of the small-scale structures. The profiles of mean velocity, resolved turbulent kinetic energy and resolved Reynolds shear stress are found to be similar among all the simulations, indicating mean quantities are relatively insensitive to turbulence modelling and grid resolution. The power spectra density of the pressure fluctuations show that LES is more capable of resolving energies in high-frequency range than DDES. After computing the normalised wavenumber-frequency spectra of fluctuating pressure on the window, we further carried out the wavenumber-frequency decomposition to separate the acoustic and the hydrodynamic components from the pressure fluctuations. The energy distribution shows that the acoustic energy has a much slower decaying rate in the high-frequency range than the hydrodynamic energy. In addition, the space-averaged sound pressure levels of pressure fluctuations on the window indicate that the present simulation with a high-order method is able to improve the accuracy in predicting pressure spectra. Finally, we carry out proper orthogonal decomposition to extract the dominating features of the decomposed acoustic and hydrodynamic components of pressure fluctuation. Patterns of multi-scale turbulence in hydrodynamic modes and propagating wavefronts of cylinder shape in acoustic modes are identified. The present research indicates that a relatively coarse grid is still capable of resolving fluctuating quantities of energy-containing structures, and LES is suggested against DDES when near-wall aerodynamic noise is the main concern.
{"title":"On turbulent flow and aerodynamic noise of generic side-view mirror with cell-centred finite difference method","authors":"Fei Liao","doi":"10.1080/14685248.2022.2037621","DOIUrl":"https://doi.org/10.1080/14685248.2022.2037621","url":null,"abstract":"This paper investigates the turbulent flow and aerodynamic noise of a half-cylinder body mounted on a flat plate at using high-order cell-centred finite difference method with delayed detached-eddy simulation (DDES) and large-eddy simulation (LES). Transient flow patterns from the two simulations are found to be very different in consideration of the small-scale structures. The profiles of mean velocity, resolved turbulent kinetic energy and resolved Reynolds shear stress are found to be similar among all the simulations, indicating mean quantities are relatively insensitive to turbulence modelling and grid resolution. The power spectra density of the pressure fluctuations show that LES is more capable of resolving energies in high-frequency range than DDES. After computing the normalised wavenumber-frequency spectra of fluctuating pressure on the window, we further carried out the wavenumber-frequency decomposition to separate the acoustic and the hydrodynamic components from the pressure fluctuations. The energy distribution shows that the acoustic energy has a much slower decaying rate in the high-frequency range than the hydrodynamic energy. In addition, the space-averaged sound pressure levels of pressure fluctuations on the window indicate that the present simulation with a high-order method is able to improve the accuracy in predicting pressure spectra. Finally, we carry out proper orthogonal decomposition to extract the dominating features of the decomposed acoustic and hydrodynamic components of pressure fluctuation. Patterns of multi-scale turbulence in hydrodynamic modes and propagating wavefronts of cylinder shape in acoustic modes are identified. The present research indicates that a relatively coarse grid is still capable of resolving fluctuating quantities of energy-containing structures, and LES is suggested against DDES when near-wall aerodynamic noise is the main concern.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46137781","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 : 2022-02-27DOI: 10.1080/14685248.2022.2043552
D. Sarkar, E. Savory
A simple set of equations, capable of quantifying and predicting the spatial decay of freestream turbulence (FST) is derived in the current study. The prediction equations are based on the inviscid estimate of the turbulent kinetic energy (TKE) dissipation rate. The new set of model equations includes the integral length scale and the turbulent kinetic energy as variables and is superior to the previous set of decay equations because, unlike those, they are not dependent on any physical grid parameters (b or M). This new set of equations, when compared and validated against 17 sets (2 active grids, 2 multi-scale grids, 9 square-cross-sectioned grids and 4 circular cross-sectioned grids) of previous, well-accepted, experimental data, including those relating to grid-generated turbulence and covering a wide range of turbulent Reynolds number (ReLu 0) (7.5 × 101 to 6.9 × 104), where Lu 0 is the initial integral length scale, showed very good agreement (within ±15%). This set of correlation equations can be used to estimate the local and/or initial turbulent kinetic energy and integral length scale (Lu ) in an FST flow and to locate the region within a flow domain where nearly-constant turbulence conditions are expected to prevail.
{"title":"A prediction method for spatially decaying freestream turbulence","authors":"D. Sarkar, E. Savory","doi":"10.1080/14685248.2022.2043552","DOIUrl":"https://doi.org/10.1080/14685248.2022.2043552","url":null,"abstract":"A simple set of equations, capable of quantifying and predicting the spatial decay of freestream turbulence (FST) is derived in the current study. The prediction equations are based on the inviscid estimate of the turbulent kinetic energy (TKE) dissipation rate. The new set of model equations includes the integral length scale and the turbulent kinetic energy as variables and is superior to the previous set of decay equations because, unlike those, they are not dependent on any physical grid parameters (b or M). This new set of equations, when compared and validated against 17 sets (2 active grids, 2 multi-scale grids, 9 square-cross-sectioned grids and 4 circular cross-sectioned grids) of previous, well-accepted, experimental data, including those relating to grid-generated turbulence and covering a wide range of turbulent Reynolds number (ReLu 0) (7.5 × 101 to 6.9 × 104), where Lu 0 is the initial integral length scale, showed very good agreement (within ±15%). This set of correlation equations can be used to estimate the local and/or initial turbulent kinetic energy and integral length scale (Lu ) in an FST flow and to locate the region within a flow domain where nearly-constant turbulence conditions are expected to prevail.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41745909","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 : 2022-01-20DOI: 10.1080/14685248.2021.2009843
Rutuja A Chavan, Anurag Sharma, B. Kumar
In this work, experimental investigations have been pursued to analyse the Reynolds stress anisotropy in the flow around the bridge pier for no seepage and downward seepage. Experiments were conducted in the non-uniform sand bed channel with circular piers of 75 mm diameter. The streamwise velocity and Reynolds Shear Stress was observed to be maximum near the edge at upstream and near the bed at downstream of pier. The strength of reversal flow diminished with downward seepage. The turbulent kinetic energy at upstream of pier found to be decreased with seepage. Decreased Strouhal number with seepage indicates the diminishing strength of wake vortices. The results present the estimation of the deviation measure from the isotropic turbulence in terms of Reynolds stress tensor for whole flow depth (within and above the scour hole zone) at the upstream and downstream sections of the pier. The streamwise profile of anisotropy tensor within the scour hole zone of the upstream section demonstrates a lesser anisotropic stream in the presence of seepage flow, while transverse and vertical components of anisotropy tensor provide the higher anisotropic stream. The results are quite the opposite in the case of the downstream section of the pier. The present study also analysed the anisotropic invariant maps in terms of Lumley triangle, Eigenvalues, and the invariant functions for the whole flow depth. The anisotropic invariant maps inclining to be two-component isotropy within the scour hole zone for both the section of the pier. With the increase in flow depth that is at the edge of scour hole, the data sets of anisotropic invariant maps show a trend of one-component isotropy, while it has an affinity to develop three-component isotropy near the free surface. Invariant function measurement presents better two-component isotropy within the scour hole zone and quasi-three component isotropy in the outer zone of scour hole for the upstream section of pier. The experimental results provide a qualitative understanding of the evolution of the Reynolds stress anisotropy tensor in the pier-affected alluvial channel.
{"title":"Turbulence anisotropy around bridge piers in seepage affected sand bed channel","authors":"Rutuja A Chavan, Anurag Sharma, B. Kumar","doi":"10.1080/14685248.2021.2009843","DOIUrl":"https://doi.org/10.1080/14685248.2021.2009843","url":null,"abstract":"In this work, experimental investigations have been pursued to analyse the Reynolds stress anisotropy in the flow around the bridge pier for no seepage and downward seepage. Experiments were conducted in the non-uniform sand bed channel with circular piers of 75 mm diameter. The streamwise velocity and Reynolds Shear Stress was observed to be maximum near the edge at upstream and near the bed at downstream of pier. The strength of reversal flow diminished with downward seepage. The turbulent kinetic energy at upstream of pier found to be decreased with seepage. Decreased Strouhal number with seepage indicates the diminishing strength of wake vortices. The results present the estimation of the deviation measure from the isotropic turbulence in terms of Reynolds stress tensor for whole flow depth (within and above the scour hole zone) at the upstream and downstream sections of the pier. The streamwise profile of anisotropy tensor within the scour hole zone of the upstream section demonstrates a lesser anisotropic stream in the presence of seepage flow, while transverse and vertical components of anisotropy tensor provide the higher anisotropic stream. The results are quite the opposite in the case of the downstream section of the pier. The present study also analysed the anisotropic invariant maps in terms of Lumley triangle, Eigenvalues, and the invariant functions for the whole flow depth. The anisotropic invariant maps inclining to be two-component isotropy within the scour hole zone for both the section of the pier. With the increase in flow depth that is at the edge of scour hole, the data sets of anisotropic invariant maps show a trend of one-component isotropy, while it has an affinity to develop three-component isotropy near the free surface. Invariant function measurement presents better two-component isotropy within the scour hole zone and quasi-three component isotropy in the outer zone of scour hole for the upstream section of pier. The experimental results provide a qualitative understanding of the evolution of the Reynolds stress anisotropy tensor in the pier-affected alluvial channel.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45711250","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 : 2022-01-18DOI: 10.1080/14685248.2021.2014058
Gazi Hasanuzzaman, S. Merbold, V. Motuz, C. Egbers
Uniform blowing through a permeable surface acts as an active flow control method in wall bounded flows. Such control technique was investigated in a zero pressure gradient turbulent boundary layer over a flat plate. Measurement data were obtained with the help of Laser Doppler Anemometry technique. Besides the drag reduction characteristics of such flow control method, time averaged measurement of stream-wise and wall-normal velocity components was taken at Reynolds number based on momentum thickness ( ) of 1100–3670. Due to the difference in surface condition with and without blowing, mean properties of the boundary condition at wall influence the flow properties when scaled with outer scaling properties. Enhanced turbulence is observed in Reynolds stresses using statistical analysis including the thickening of the boundary layer.
{"title":"Enhanced outer peaks in turbulent boundary layer using uniform blowing at moderate Reynolds number","authors":"Gazi Hasanuzzaman, S. Merbold, V. Motuz, C. Egbers","doi":"10.1080/14685248.2021.2014058","DOIUrl":"https://doi.org/10.1080/14685248.2021.2014058","url":null,"abstract":"Uniform blowing through a permeable surface acts as an active flow control method in wall bounded flows. Such control technique was investigated in a zero pressure gradient turbulent boundary layer over a flat plate. Measurement data were obtained with the help of Laser Doppler Anemometry technique. Besides the drag reduction characteristics of such flow control method, time averaged measurement of stream-wise and wall-normal velocity components was taken at Reynolds number based on momentum thickness ( ) of 1100–3670. Due to the difference in surface condition with and without blowing, mean properties of the boundary condition at wall influence the flow properties when scaled with outer scaling properties. Enhanced turbulence is observed in Reynolds stresses using statistical analysis including the thickening of the boundary layer.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41314850","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 : 2022-01-03DOI: 10.1080/14685248.2022.2097688
R. Volino, W. Devenport, U. Piomelli
The prediction of turbulent flows over rough surfaces is important for many applications in engineering and in the natural sciences. Since the resolution of the roughness requires significant computational resources, most modelling approaches rely on the related concepts of ‘equivalent sand-grain roughness’ and ‘wall similarity’. While the validity of these concepts is well established for zero-pressure-gradient boundary-layers and for channel flows, such is not the case for non-equilibrium conditions. This raises a number of important questions, some of which are discussed in this paper. We also suggest some possible paths to answering these questions.
{"title":"Questions on the effects of roughness and its analysis in non-equilibrium flows","authors":"R. Volino, W. Devenport, U. Piomelli","doi":"10.1080/14685248.2022.2097688","DOIUrl":"https://doi.org/10.1080/14685248.2022.2097688","url":null,"abstract":"The prediction of turbulent flows over rough surfaces is important for many applications in engineering and in the natural sciences. Since the resolution of the roughness requires significant computational resources, most modelling approaches rely on the related concepts of ‘equivalent sand-grain roughness’ and ‘wall similarity’. While the validity of these concepts is well established for zero-pressure-gradient boundary-layers and for channel flows, such is not the case for non-equilibrium conditions. This raises a number of important questions, some of which are discussed in this paper. We also suggest some possible paths to answering these questions.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49162573","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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