Pub Date : 2021-09-12DOI: 10.1080/14685248.2021.1973015
Vishal Kumar, U. Piomelli, O. Lehmkuhl
ABSTRACT We performed large-eddy simulations of the flow over an aerofoil to understand the effects of leading-edge roughness designed to mimic ice accretion. The roughness elements protrude outside the boundary layer, which, near the leading edge, is very thin; thus, the configuration does not represent a classical rough-wall boundary layer, but rather the flow over macroscopic obstacles. A grid convergence study is conducted and results are validated by comparison to numerical and experimental studies in the literature. The main effect of the obstacles is to accelerate transition to turbulence. Significant variations in structure generation are observed for different roughness shapes. The three-dimensionality of the irregularities has a strong impact on the flow: it creates alternating regions of high-speed (‘peaks’) and low-speed (‘valleys’) regions, a phenomenon termed ‘channelling’. The valley regions resemble a decelerating boundary layer: they exhibit considerable wake and higher levels of Reynolds stresses. The peak regions, on the other hand, are more similar to an accelerating one. Implications of the channelling phenomenon on turbulence modelling are discussed.
{"title":"Large-eddy simulations of the flow on an aerofoil with leading-edge imperfections","authors":"Vishal Kumar, U. Piomelli, O. Lehmkuhl","doi":"10.1080/14685248.2021.1973015","DOIUrl":"https://doi.org/10.1080/14685248.2021.1973015","url":null,"abstract":"ABSTRACT We performed large-eddy simulations of the flow over an aerofoil to understand the effects of leading-edge roughness designed to mimic ice accretion. The roughness elements protrude outside the boundary layer, which, near the leading edge, is very thin; thus, the configuration does not represent a classical rough-wall boundary layer, but rather the flow over macroscopic obstacles. A grid convergence study is conducted and results are validated by comparison to numerical and experimental studies in the literature. The main effect of the obstacles is to accelerate transition to turbulence. Significant variations in structure generation are observed for different roughness shapes. The three-dimensionality of the irregularities has a strong impact on the flow: it creates alternating regions of high-speed (‘peaks’) and low-speed (‘valleys’) regions, a phenomenon termed ‘channelling’. The valley regions resemble a decelerating boundary layer: they exhibit considerable wake and higher levels of Reynolds stresses. The peak regions, on the other hand, are more similar to an accelerating one. Implications of the channelling phenomenon on turbulence modelling are discussed.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"22 1","pages":"735 - 760"},"PeriodicalIF":1.9,"publicationDate":"2021-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46085618","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 : 2021-09-11DOI: 10.1080/14685248.2021.1973013
M. Bernardini, E. J. García Cartagena, A. Mohammadi, A. Smits, S. Leonardi
Direct numerical simulations of a turbulent channel with liquid infused surfaces made of longitudinal micro-ridges have been performed to study the effect of texture geometry and interface deformation. The flow conditions consider a viscosity ratio , several values of the micro-ridge pitch and two different Weber numbers, We = 0 and We = 50. The performance is analyzed in terms of drag reduction (DR) with respect to an equivalent smooth channel, and the results compared with those available for super-hydrophobic surfaces (SHS). It is found that, due to the relatively high viscosity of the liquid locked in the substrate, the drag reduction offered by LIS is substantially lower than the corresponding SHS. When reported in terms of the streamwise slip length normalized in wall units, the amount of DR obtained by LIS in the ideal case of flat interface collapses on the SHS data. The interface dynamics has a detrimental effect on the performance, that becomes particularly severe when the pitch increases. The degradation of DR is well parametrized by the log-law shift of the velocity profile, that is found to be proportional to the difference between the virtual origin of the mean flow and that experienced by the overlying turbulence.
{"title":"Turbulent drag reduction over liquid-infused textured surfaces: effect of the interface dynamics","authors":"M. Bernardini, E. J. García Cartagena, A. Mohammadi, A. Smits, S. Leonardi","doi":"10.1080/14685248.2021.1973013","DOIUrl":"https://doi.org/10.1080/14685248.2021.1973013","url":null,"abstract":"Direct numerical simulations of a turbulent channel with liquid infused surfaces made of longitudinal micro-ridges have been performed to study the effect of texture geometry and interface deformation. The flow conditions consider a viscosity ratio , several values of the micro-ridge pitch and two different Weber numbers, We = 0 and We = 50. The performance is analyzed in terms of drag reduction (DR) with respect to an equivalent smooth channel, and the results compared with those available for super-hydrophobic surfaces (SHS). It is found that, due to the relatively high viscosity of the liquid locked in the substrate, the drag reduction offered by LIS is substantially lower than the corresponding SHS. When reported in terms of the streamwise slip length normalized in wall units, the amount of DR obtained by LIS in the ideal case of flat interface collapses on the SHS data. The interface dynamics has a detrimental effect on the performance, that becomes particularly severe when the pitch increases. The degradation of DR is well parametrized by the log-law shift of the velocity profile, that is found to be proportional to the difference between the virtual origin of the mean flow and that experienced by the overlying turbulence.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"22 1","pages":"681 - 712"},"PeriodicalIF":1.9,"publicationDate":"2021-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42928764","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 : 2021-09-11DOI: 10.1080/14685248.2021.1974466
Fulin Tong, J. Duan, Xinliang Li
The wall-shear stress (WSS) fluctuations in the interaction of an oblique shock wave with a flat-plate turbulent boundary layer are investigated by means of direct numerical simulation (DNS) at Mach 2.25. The numerical results agree very well with previous experiments and DNS data in terms of turbulence statistics, wall pressure, and skin friction. The fluctuating WSS characteristics, including probability density function (PDF), frequency spectrum, space–time correlation, and convection velocity, are analysed systematically. It is found that the positively skewed PDF shape of the streamwise WSS fluctuations is significantly changed due to the presence of a separation bubble, while the PDF shape of the spanwise component is slightly affected, exhibiting a symmetric behaviour across the interaction. The weighted power-spectrum density map indicates that the low-frequency unsteadiness associated with the separated shock - exhibits little influence on the spectrum for either component, and no enhancement of the low-frequency energy is observed. A significant reduction in the spatial extent of the two-point correlation is observed, causing spanwise elongated coherence for the streamwise WSS fluctuations in the separation region. Moreover, the elliptic behaviour of the space–time correlations is essentially preserved throughout the interaction, and this is accompanied by a sudden reduction of the convection velocity in the separation bubble.
{"title":"Characteristics of wall-shear stress fluctuations in shock wave and turbulent boundary layer interaction","authors":"Fulin Tong, J. Duan, Xinliang Li","doi":"10.1080/14685248.2021.1974466","DOIUrl":"https://doi.org/10.1080/14685248.2021.1974466","url":null,"abstract":"The wall-shear stress (WSS) fluctuations in the interaction of an oblique shock wave with a flat-plate turbulent boundary layer are investigated by means of direct numerical simulation (DNS) at Mach 2.25. The numerical results agree very well with previous experiments and DNS data in terms of turbulence statistics, wall pressure, and skin friction. The fluctuating WSS characteristics, including probability density function (PDF), frequency spectrum, space–time correlation, and convection velocity, are analysed systematically. It is found that the positively skewed PDF shape of the streamwise WSS fluctuations is significantly changed due to the presence of a separation bubble, while the PDF shape of the spanwise component is slightly affected, exhibiting a symmetric behaviour across the interaction. The weighted power-spectrum density map indicates that the low-frequency unsteadiness associated with the separated shock - exhibits little influence on the spectrum for either component, and no enhancement of the low-frequency energy is observed. A significant reduction in the spatial extent of the two-point correlation is observed, causing spanwise elongated coherence for the streamwise WSS fluctuations in the separation region. Moreover, the elliptic behaviour of the space–time correlations is essentially preserved throughout the interaction, and this is accompanied by a sudden reduction of the convection velocity in the separation bubble.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"22 1","pages":"761 - 783"},"PeriodicalIF":1.9,"publicationDate":"2021-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47144787","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 : 2021-09-11DOI: 10.1080/14685248.2021.1973012
Haoliang Yu, U. Ciri, A. Malik, S. Leonardi
A reduced-order model (ROM) is proposed for efficient drag prediction on a streamlined body with surface imperfections that emulate leading-edge roughness or erosion-induced damage. Surface imperfections are idealised as forward-facing step(s) for which the chordwise position, spanwise length, and distribution of steps are varied. It is hypothesised that superposed a bilinear dependencies on the chordwise location and spanwise length of individual steps comprising the damage provide for reasonable ROM predictions of the corresponding change in total drag on the streamlined body. Direct numerical simulations are applied to test the ROM hypotheses and to study interactions between the three-dimensional steps and the separated near-wall turbulent flow fields, justifying the underlying terms and form of the ROM. Insights into the flow physics influencing both form and friction contributions to total drag are revealed, and satisfactory model performance is demonstrated for complex damage idealisations that emulate fracture of laminated wind turbine blades.
{"title":"A simplified model for drag evaluation of a streamlined body with leading-edge damage","authors":"Haoliang Yu, U. Ciri, A. Malik, S. Leonardi","doi":"10.1080/14685248.2021.1973012","DOIUrl":"https://doi.org/10.1080/14685248.2021.1973012","url":null,"abstract":"A reduced-order model (ROM) is proposed for efficient drag prediction on a streamlined body with surface imperfections that emulate leading-edge roughness or erosion-induced damage. Surface imperfections are idealised as forward-facing step(s) for which the chordwise position, spanwise length, and distribution of steps are varied. It is hypothesised that superposed a bilinear dependencies on the chordwise location and spanwise length of individual steps comprising the damage provide for reasonable ROM predictions of the corresponding change in total drag on the streamlined body. Direct numerical simulations are applied to test the ROM hypotheses and to study interactions between the three-dimensional steps and the separated near-wall turbulent flow fields, justifying the underlying terms and form of the ROM. Insights into the flow physics influencing both form and friction contributions to total drag are revealed, and satisfactory model performance is demonstrated for complex damage idealisations that emulate fracture of laminated wind turbine blades.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"22 1","pages":"656 - 679"},"PeriodicalIF":1.9,"publicationDate":"2021-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46642631","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 : 2021-09-11DOI: 10.1080/14685248.2021.1973014
F. Chedevergne
The discrete element (roughness) method developed a few decades ago is revisited using the double-averaging technique applied to the Navier-Stokes equation. A -based DANS turbulence model is thus derived to be able to account for roughness effects. Several closure relations are proposed to model all terms induced by the use of the double averaging. The momentum and energy equations are considered in their simplified forms adapted to a 1D channel code in accordance with the DNS results used for the validation. To reconcile the discrete element (roughness) method with the double-averaged Navier-Stokes equations the notion of representative elementary roughness is introduced. A large validation dataset coming from various DNS configurations is then used to assess the predictions of the proposed DANS model. Yet not fully complete, especially regarding the dispersive terms due to a lack of data, the performed validation already proves the overall excellent behaviour of the DANS model and demonstrates the relevance of the present methodology based on the representative elementary roughness.
{"title":"A double-averaged Navier-Stokes k – ω turbulence model for wall flows over rough surfaces with heat transfer","authors":"F. Chedevergne","doi":"10.1080/14685248.2021.1973014","DOIUrl":"https://doi.org/10.1080/14685248.2021.1973014","url":null,"abstract":"The discrete element (roughness) method developed a few decades ago is revisited using the double-averaging technique applied to the Navier-Stokes equation. A -based DANS turbulence model is thus derived to be able to account for roughness effects. Several closure relations are proposed to model all terms induced by the use of the double averaging. The momentum and energy equations are considered in their simplified forms adapted to a 1D channel code in accordance with the DNS results used for the validation. To reconcile the discrete element (roughness) method with the double-averaged Navier-Stokes equations the notion of representative elementary roughness is introduced. A large validation dataset coming from various DNS configurations is then used to assess the predictions of the proposed DANS model. Yet not fully complete, especially regarding the dispersive terms due to a lack of data, the performed validation already proves the overall excellent behaviour of the DANS model and demonstrates the relevance of the present methodology based on the representative elementary roughness.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"22 1","pages":"713 - 734"},"PeriodicalIF":1.9,"publicationDate":"2021-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42182453","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 : 2021-07-27DOI: 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":"22 1","pages":"640 - 655"},"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":"22 1","pages":"413 - 433"},"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":"22 1","pages":"434 - 460"},"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":"23 1","pages":"1 - 28"},"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":"22 1","pages":"597 - 622"},"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}
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