Pub Date : 2021-07-27DOI: 10.1080/14685248.2021.1955121
M. Khashehchi, Z. Harun, Yasser Mahmoudi Larimi
Tomographic particle image velocimetry (Tomo-PIV) was performed to study the initial transition process formed in a free round jet between the laminar flow at the jet exit, and the fully turbulent flow region at Red = 6500. The evolution of the small-scale turbulence characteristics in this particular region has been assessed by means of the invariants of the velocity gradient tensor (VGT). These invariants enable us to study the dynamics, geometry, and topology of the turbulence phenomena. A mapping from the three-dimensional flow fields to a two-dimensional invariants plane is used to analyse the dissipation of kinetic energy at small-scales and the amplification of local vorticity due to vortex stretching. A systematic study of the event that represents the persistent alignment of the vorticity vector with the second eigenvector of the rate of strain tensor was examined, and the results of this phenomenon at the near-field of the jet are discussed. Results show that vorticity vector, ω, maintains its alignment with the intermediate eigenvector of the rate of strain tensor, υ 2, in the developing region by either the rotation of the intermediate eigenframe or the tilting of ω.
{"title":"Evolution of the invariants of the velocity gradient tensor in the developing region of a round jet using tomographic PIV","authors":"M. Khashehchi, Z. Harun, Yasser Mahmoudi Larimi","doi":"10.1080/14685248.2021.1955121","DOIUrl":"https://doi.org/10.1080/14685248.2021.1955121","url":null,"abstract":"Tomographic particle image velocimetry (Tomo-PIV) was performed to study the initial transition process formed in a free round jet between the laminar flow at the jet exit, and the fully turbulent flow region at Red = 6500. The evolution of the small-scale turbulence characteristics in this particular region has been assessed by means of the invariants of the velocity gradient tensor (VGT). These invariants enable us to study the dynamics, geometry, and topology of the turbulence phenomena. A mapping from the three-dimensional flow fields to a two-dimensional invariants plane is used to analyse the dissipation of kinetic energy at small-scales and the amplification of local vorticity due to vortex stretching. A systematic study of the event that represents the persistent alignment of the vorticity vector with the second eigenvector of the rate of strain tensor was examined, and the results of this phenomenon at the near-field of the jet are discussed. Results show that vorticity vector, ω, maintains its alignment with the intermediate eigenvector of the rate of strain tensor, υ 2, in the developing region by either the rotation of the intermediate eigenframe or the tilting of ω.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1955121","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42541587","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 : 2021-07-03DOI: 10.1080/14685248.2021.1915494
T. Ohta, Keisuke Nakatsuji
Direct numerical simulations of turbulent boundary layers with roughness elements on a wall were performed to investigate the spatial characteristics of rough-wall turbulence and establish a corresponding prediction method. When the roughness height was larger than the buffer layer, the rough-wall turbulence exhibited different spatial characteristics of the turbulence structures from those pertaining to a smooth wall. A novel spatial scaling method was established to examine the universal spatial characteristics of turbulence structures in the presence and absence of wall roughness. Specifically, the viscous length was determined by modifying the definition of the friction velocity in the region in which the roughness influenced the flow. The rough-wall turbulence could be accurately predicted by performing large eddy simulations using the subgrid scale model with the filter width, which was modified using the proposed spatial scaling method. The proposed model can be used to design more efficient fluid machinery in engineering applications.
{"title":"Spatial-scaling method and modified large eddy simulation to examine rough-wall turbulence","authors":"T. Ohta, Keisuke Nakatsuji","doi":"10.1080/14685248.2021.1915494","DOIUrl":"https://doi.org/10.1080/14685248.2021.1915494","url":null,"abstract":"Direct numerical simulations of turbulent boundary layers with roughness elements on a wall were performed to investigate the spatial characteristics of rough-wall turbulence and establish a corresponding prediction method. When the roughness height was larger than the buffer layer, the rough-wall turbulence exhibited different spatial characteristics of the turbulence structures from those pertaining to a smooth wall. A novel spatial scaling method was established to examine the universal spatial characteristics of turbulence structures in the presence and absence of wall roughness. Specifically, the viscous length was determined by modifying the definition of the friction velocity in the region in which the roughness influenced the flow. The rough-wall turbulence could be accurately predicted by performing large eddy simulations using the subgrid scale model with the filter width, which was modified using the proposed spatial scaling method. The proposed model can be used to design more efficient fluid machinery in engineering applications.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1915494","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43931365","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 : 2021-07-03DOI: 10.1080/14685248.2021.1927057
S. C. Mangavelli, J. Yuan, G. Brereton
The dynamical effects of roughness geometry on the response of a half-height turbulent channel flow to an impulse acceleration are investigated using direct numerical simulations. Two rough surfaces different in the surface height spectrum are compared between themselves and with a smooth-wall baseline case. Both rough cases develop from a transitionally rough state to a fully rough one. Results show that on rough walls the thickness of the roughness sublayer (RSL), defined as the layer with significant form-induced stresses, stays almost constant. The ensemble-average flows inside the RSL stays close to equilibrium throughout the transient. This is shown by the form-induced perturbations largely scaling with the mean velocity at the edge of the RSL. Inside the RSL, turbulence develops rapidly to the new steady state, accompanied by substantial changes in the Reynolds stress balance. In contrast, the flow above the RSL recovers long after the sublayer is fully developed, without a significant change in Reynolds stress balance. The geometry of the roughness plays an important role in determining the rate of response of turbulence throughout the boundary layer. This work provides detailed explanation of the suppression of reverse transition by surface roughness in response to a mean flow acceleration.
{"title":"Effects of surface roughness topography in transient channel flows","authors":"S. C. Mangavelli, J. Yuan, G. Brereton","doi":"10.1080/14685248.2021.1927057","DOIUrl":"https://doi.org/10.1080/14685248.2021.1927057","url":null,"abstract":"The dynamical effects of roughness geometry on the response of a half-height turbulent channel flow to an impulse acceleration are investigated using direct numerical simulations. Two rough surfaces different in the surface height spectrum are compared between themselves and with a smooth-wall baseline case. Both rough cases develop from a transitionally rough state to a fully rough one. Results show that on rough walls the thickness of the roughness sublayer (RSL), defined as the layer with significant form-induced stresses, stays almost constant. The ensemble-average flows inside the RSL stays close to equilibrium throughout the transient. This is shown by the form-induced perturbations largely scaling with the mean velocity at the edge of the RSL. Inside the RSL, turbulence develops rapidly to the new steady state, accompanied by substantial changes in the Reynolds stress balance. In contrast, the flow above the RSL recovers long after the sublayer is fully developed, without a significant change in Reynolds stress balance. The geometry of the roughness plays an important role in determining the rate of response of turbulence throughout the boundary layer. This work provides detailed explanation of the suppression of reverse transition by surface roughness in response to a mean flow acceleration.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1927057","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47141280","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 : 2021-06-30DOI: 10.1080/14685248.2021.1999459
Haitz S'aez de Oc'ariz Borde, David Sondak, P. Protopapas
The Reynolds-averaged Navier-Stokes (RANS) equations are widely used in turbulence applications. They require accurately modelling the anisotropic Reynolds stress tensor, for which traditional Reynolds stress closure models only yield reliable results in some flow configurations. In the last few years, there has been a surge of work aiming at using data-driven approaches to tackle this problem. The majority of previous work has focused on the development of fully connected networks for modelling the anisotropic Reynolds stress tensor. In this paper, we expand upon recent work for turbulent channel flow and develop new convolutional neural network (CNN) models that are able to accurately predict the normalised anisotropic Reynolds stress tensor. We apply the new CNN model to a number of one-dimensional turbulent flows. Additionally, we present interpretability techniques that help drive the model design and provide guidance on the model behaviour in relation to the underlying physics.
{"title":"Convolutional neural network models and interpretability for the anisotropic reynolds stress tensor in turbulent one-dimensional flows","authors":"Haitz S'aez de Oc'ariz Borde, David Sondak, P. Protopapas","doi":"10.1080/14685248.2021.1999459","DOIUrl":"https://doi.org/10.1080/14685248.2021.1999459","url":null,"abstract":"The Reynolds-averaged Navier-Stokes (RANS) equations are widely used in turbulence applications. They require accurately modelling the anisotropic Reynolds stress tensor, for which traditional Reynolds stress closure models only yield reliable results in some flow configurations. In the last few years, there has been a surge of work aiming at using data-driven approaches to tackle this problem. The majority of previous work has focused on the development of fully connected networks for modelling the anisotropic Reynolds stress tensor. In this paper, we expand upon recent work for turbulent channel flow and develop new convolutional neural network (CNN) models that are able to accurately predict the normalised anisotropic Reynolds stress tensor. We apply the new CNN model to a number of one-dimensional turbulent flows. Additionally, we present interpretability techniques that help drive the model design and provide guidance on the model behaviour in relation to the underlying physics.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48274394","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 : 2021-06-29DOI: 10.1080/14685248.2021.1944634
T. Ohta, T. Yonemura, Yasuyuki Sakai
This study was aimed at examining the influence of the system rotation as an external action on the development of vortical structures and combustion. Specifically, three-dimensional direct numerical simulations of compressible mixing layers with non-premixed /air combustion were performed using a detailed chemical reaction scheme. The relationship between the developing vortical structures and chemical reactions in the flow field with the rotation was investigated. The development of combustion changed depending on the vortical structures, and the presence of roller vortices promoted the combustion phenomena. The influence of the vortical structures on the elementary reactions, which contribute to the heat release rate, was small. During the anticyclonic rotation, the roller vortices collapsed and suppressed the combustion. In contrast, the cyclonic rotation resulted in the generation of quasi-2D roller vortices, which enlarged the high-heat-release-rate regions and promoted the combustion. Overall, the vortical structures induced by the rotation can change the development of combustion even though the elementary reactions that contribute to the heat release rate remain unchanged. The presented findings can guide the prediction and control of turbulent combustion in practical situations involving fluid machinery.
{"title":"Numerical investigation of the effect of rotation on non-premixed hydrogen combustion in developing turbulent mixing layers","authors":"T. Ohta, T. Yonemura, Yasuyuki Sakai","doi":"10.1080/14685248.2021.1944634","DOIUrl":"https://doi.org/10.1080/14685248.2021.1944634","url":null,"abstract":"This study was aimed at examining the influence of the system rotation as an external action on the development of vortical structures and combustion. Specifically, three-dimensional direct numerical simulations of compressible mixing layers with non-premixed /air combustion were performed using a detailed chemical reaction scheme. The relationship between the developing vortical structures and chemical reactions in the flow field with the rotation was investigated. The development of combustion changed depending on the vortical structures, and the presence of roller vortices promoted the combustion phenomena. The influence of the vortical structures on the elementary reactions, which contribute to the heat release rate, was small. During the anticyclonic rotation, the roller vortices collapsed and suppressed the combustion. In contrast, the cyclonic rotation resulted in the generation of quasi-2D roller vortices, which enlarged the high-heat-release-rate regions and promoted the combustion. Overall, the vortical structures induced by the rotation can change the development of combustion even though the elementary reactions that contribute to the heat release rate remain unchanged. The presented findings can guide the prediction and control of turbulent combustion in practical situations involving fluid machinery.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1944634","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48533188","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 : 2021-06-03DOI: 10.1080/14685248.2021.1916023
J. Cheng, Jianzhao Wu, Yu-lu Liu, Zhiming Lu
Spontaneous and stochastic reversal of large scale flow structure is an intriguing and crucial phenomenon in turbulent Rayleigh-Bénard type natural convection. This paper proposes a new control approach to eliminate the reversals through stabilising the corner flows using two small sidewall controllers. Based on a series of direct numerical simulations, it is shown that the control can successfully stop the growth of corner vortices and suppress the reversal of large-scale circulation, if the width of sidewall controllers installed within or near the top of corner vortices is large enough. When the controllers are located around the centre, they can easily break up the large-scale structures or even divide the single roll mode into a double-roll mode for very large widths. Moreover, the influence of sidewall controllers on the heat transport is studied. It is shown that the heat transport efficiency can be slightly enhanced or suppressed when the proper location and width are chosen. The present findings provide a new idea to control the large-scale flow structure and reversals in thermally driven convection through sidewall controlling.
{"title":"Sidewall controlling large-scale flow structure and reversal in turbulent Rayleigh-Bénard convection","authors":"J. Cheng, Jianzhao Wu, Yu-lu Liu, Zhiming Lu","doi":"10.1080/14685248.2021.1916023","DOIUrl":"https://doi.org/10.1080/14685248.2021.1916023","url":null,"abstract":"Spontaneous and stochastic reversal of large scale flow structure is an intriguing and crucial phenomenon in turbulent Rayleigh-Bénard type natural convection. This paper proposes a new control approach to eliminate the reversals through stabilising the corner flows using two small sidewall controllers. Based on a series of direct numerical simulations, it is shown that the control can successfully stop the growth of corner vortices and suppress the reversal of large-scale circulation, if the width of sidewall controllers installed within or near the top of corner vortices is large enough. When the controllers are located around the centre, they can easily break up the large-scale structures or even divide the single roll mode into a double-roll mode for very large widths. Moreover, the influence of sidewall controllers on the heat transport is studied. It is shown that the heat transport efficiency can be slightly enhanced or suppressed when the proper location and width are chosen. The present findings provide a new idea to control the large-scale flow structure and reversals in thermally driven convection through sidewall controlling.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1916023","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48249710","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 : 2021-06-03DOI: 10.1080/14685248.2021.1932947
E. Juntasaro, K. Ngiamsoongnirn, Phongsakorn Thawornsathit, P. Durbin
ABSTRACT The objective of this paper is to propose a new intermittency transport equation that is naturally capable of capturing the effects of free-stream turbulence and pressure gradient on bypass and natural transition without need for any extra parameters/terms to take into account the free-stream turbulence and the pressure gradient. This new intermittency transport equation is obtained by derivation and, in it, only its production term is modeled via two empirical functions in order to detect the onset location of transition and to control the growth rate of transition process. Only one sensing parameter is used to detect the transition onset for both natural and bypass transition. For the purpose of not altering the original form of the base turbulence model, the effective intermittency factor is used to describe the separation-induced transition. The base turbulence model remains unmodified in conjunction with the effective intermittency factor as a regulator to control the net turbulent generation rate. For the evaluation of model performance, the modeled intermittency equation is tested against (1) the transitional boundary layer on a flat plate with zero and non-zero pressure gradients, (2) the transitional flow over a compressor blade with a laminar separation bubble, and (3) the transitional flow over a wind turbine airfoil at various angles of attack. The present results are also compared to those of the transition model of Menter et al. [1] and those of the transition model of Langtry and Menter [2]. The evaluation results reveal that the new intermittency transport equation is capable of predicting the bypass, natural and separation-induced transition.
{"title":"Development of an intermittency transport equation for modeling bypass, natural and separation-induced transition","authors":"E. Juntasaro, K. Ngiamsoongnirn, Phongsakorn Thawornsathit, P. Durbin","doi":"10.1080/14685248.2021.1932947","DOIUrl":"https://doi.org/10.1080/14685248.2021.1932947","url":null,"abstract":"ABSTRACT The objective of this paper is to propose a new intermittency transport equation that is naturally capable of capturing the effects of free-stream turbulence and pressure gradient on bypass and natural transition without need for any extra parameters/terms to take into account the free-stream turbulence and the pressure gradient. This new intermittency transport equation is obtained by derivation and, in it, only its production term is modeled via two empirical functions in order to detect the onset location of transition and to control the growth rate of transition process. Only one sensing parameter is used to detect the transition onset for both natural and bypass transition. For the purpose of not altering the original form of the base turbulence model, the effective intermittency factor is used to describe the separation-induced transition. The base turbulence model remains unmodified in conjunction with the effective intermittency factor as a regulator to control the net turbulent generation rate. For the evaluation of model performance, the modeled intermittency equation is tested against (1) the transitional boundary layer on a flat plate with zero and non-zero pressure gradients, (2) the transitional flow over a compressor blade with a laminar separation bubble, and (3) the transitional flow over a wind turbine airfoil at various angles of attack. The present results are also compared to those of the transition model of Menter et al. [1] and those of the transition model of Langtry and Menter [2]. The evaluation results reveal that the new intermittency transport equation is capable of predicting the bypass, natural and separation-induced transition.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1932947","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44563240","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 : 2021-05-31DOI: 10.1080/14685248.2021.1932944
L. Thijs, R. Dellaert, S. Tajfirooz, J. Zeegers, J. Kuerten
ABSTRACT We present an experimental and numerical study of the flow downstream of honeycomb flow straighteners for a range of Reynolds numbers, covering both laminar and turbulent flow inside the honeycomb cells. We carried out experiments with planar particle image velocimetry (PIV) in a wind tunnel and performed numerical simulations to perform an in-depth investigation of the three-dimensional flow field. The individual channel profiles downstream of the honeycomb gradually develop into one uniform velocity profile. This development corresponds with an increase in the velocity fluctuations which reach a maximum and then start to decay. The position and magnitude of the turbulence intensity peak depend on the Reynolds number. By means of the turbulence kinetic energy (TKE) budget it is shown that the production of TKE is dominated by the shear layers corresponding to the honeycomb walls. The near-field and far-field decay of the turbulence intensity can be described by power laws where we used the position where the production term of the TKE reaches its maximum as the virtual origin.
{"title":"Honeycomb-generated Reynolds-number-dependent wake turbulence","authors":"L. Thijs, R. Dellaert, S. Tajfirooz, J. Zeegers, J. Kuerten","doi":"10.1080/14685248.2021.1932944","DOIUrl":"https://doi.org/10.1080/14685248.2021.1932944","url":null,"abstract":"ABSTRACT We present an experimental and numerical study of the flow downstream of honeycomb flow straighteners for a range of Reynolds numbers, covering both laminar and turbulent flow inside the honeycomb cells. We carried out experiments with planar particle image velocimetry (PIV) in a wind tunnel and performed numerical simulations to perform an in-depth investigation of the three-dimensional flow field. The individual channel profiles downstream of the honeycomb gradually develop into one uniform velocity profile. This development corresponds with an increase in the velocity fluctuations which reach a maximum and then start to decay. The position and magnitude of the turbulence intensity peak depend on the Reynolds number. By means of the turbulence kinetic energy (TKE) budget it is shown that the production of TKE is dominated by the shear layers corresponding to the honeycomb walls. The near-field and far-field decay of the turbulence intensity can be described by power laws where we used the position where the production term of the TKE reaches its maximum as the virtual origin.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1932944","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48500723","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 : 2021-05-28DOI: 10.1080/14685248.2021.1932939
K. Chaudhury, Chandranath Banerjee, Swapnil Urankar
ABSTRACT We present a systematic approach to extract the characteristic vortex region that contains the essential features of a complex flow field. The process involves the analysis of the complex eigenvalues of the velocity gradient tensor. In particular, we propose the analysis using the joint and marginal probability distributions of the complex eigenvalues of the velocity gradient tensor that preserves the sufficient swirling strength and the required orbital compactness of the swirling orbits defining the vortex region. We consider three complex flow scenarios for the application and the assessment of the proposed approach: (i) rotating Rayleigh–Benard convection, (ii) turbulent channel flow, (iii) turbulent flow field in a cylindrical cyclonic separator. While problem (i) is considered for the extraction of subsumed cyclonic structure, problems (ii) and (iii) are reminiscent of wall-bounded turbulent flows, relevant for different industrial applications.
{"title":"Estimation of characteristic vortex structures in complex flow","authors":"K. Chaudhury, Chandranath Banerjee, Swapnil Urankar","doi":"10.1080/14685248.2021.1932939","DOIUrl":"https://doi.org/10.1080/14685248.2021.1932939","url":null,"abstract":"ABSTRACT We present a systematic approach to extract the characteristic vortex region that contains the essential features of a complex flow field. The process involves the analysis of the complex eigenvalues of the velocity gradient tensor. In particular, we propose the analysis using the joint and marginal probability distributions of the complex eigenvalues of the velocity gradient tensor that preserves the sufficient swirling strength and the required orbital compactness of the swirling orbits defining the vortex region. We consider three complex flow scenarios for the application and the assessment of the proposed approach: (i) rotating Rayleigh–Benard convection, (ii) turbulent channel flow, (iii) turbulent flow field in a cylindrical cyclonic separator. While problem (i) is considered for the extraction of subsumed cyclonic structure, problems (ii) and (iii) are reminiscent of wall-bounded turbulent flows, relevant for different industrial applications.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1932939","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45165924","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 : 2021-05-19DOI: 10.1080/14685248.2021.1925125
N. Ali, M. Calaf, R. B. Cal
For complex flow systems like the one of the wind turbine wakes, which include a range of interacting turbulent scales, there is the potential to reduce the high dimensionality of the problem to low-rank approximations. Unsupervised cluster analysis based on the proper orthogonal decomposition is used here to identify the coherent structure and transition dynamics of wind turbine wake. Through the clustering approach, the nonlinear dynamics of the turbine wake is presented in a linear framework. The features of the fluctuating velocity are grouped based on similarity and presented as the centroids of the defining clusters. Determined from probability distribution of the transition, the dynamical system identifies the features of the wakes and the inherent dynamics of the flow.
{"title":"Cluster-based probabilistic structure dynamical model of wind turbine wake","authors":"N. Ali, M. Calaf, R. B. Cal","doi":"10.1080/14685248.2021.1925125","DOIUrl":"https://doi.org/10.1080/14685248.2021.1925125","url":null,"abstract":"For complex flow systems like the one of the wind turbine wakes, which include a range of interacting turbulent scales, there is the potential to reduce the high dimensionality of the problem to low-rank approximations. Unsupervised cluster analysis based on the proper orthogonal decomposition is used here to identify the coherent structure and transition dynamics of wind turbine wake. Through the clustering approach, the nonlinear dynamics of the turbine wake is presented in a linear framework. The features of the fluctuating velocity are grouped based on similarity and presented as the centroids of the defining clusters. Determined from probability distribution of the transition, the dynamical system identifies the features of the wakes and the inherent dynamics of the flow.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-05-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1925125","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42401322","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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