Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena最新文献

{"title":"LES OF LANGMUIR TURBULENCE IN STABLY STRATIFIED FLOW","authors":"G. Martinat, A. Tejada-Martínez, C. Grosch","doi":"10.1615/tsfp8.420","DOIUrl":"https://doi.org/10.1615/tsfp8.420","url":null,"abstract":"","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"57 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124585066","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"HIGH-RESOLUTION LARGE FIELD-OF-VIEW EXPERIMENTAL INVESTIGATION OF TURBULENT CONVECTION VELOCITIES IN A TURBULENT BOUNDARY LAYER","authors":"C. Atkinson, N. Buchmann, O. Amili, J. Soria","doi":"10.1615/tsfp8.450","DOIUrl":"https://doi.org/10.1615/tsfp8.450","url":null,"abstract":"","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"114 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114825235","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Modification of Drag-reduced Flow by dosing water from the wall - Investigation of Turbulent Structure by PIV-","authors":"Yuichiro Iwaki, M. Motozawa, T. Tsukahara, Y. Kawaguchi","doi":"10.1615/tsfp8.890","DOIUrl":"https://doi.org/10.1615/tsfp8.890","url":null,"abstract":"Experimental investigation of modified drag-reduced channel flow by covering the near-wall region with pure water was carried out. To modify the near-wall turbulent structure of drag-reduced channel flow of surfactant solution, the wall-dosing apparatus, in which pure water is supplied from the porous surface of the channel wall into the viscoelastic bulk flow, was used. By covering the near-wall region with water, drag reduction rate is slightly enhanced, compared with the viscoelastic channel flow without water dosing. We examined the mechanism of this enhancement of drag reduction and the change of the turbulent structure by water dosing from instantaneous velocity fields captured by PIV. The decomposition of Cf shows that viscoelastic stress decreases largely while Reynolds shear stress increases, which causes drag reduction to be enhanced. Moreover, characteristic turbulent structures were observed in the instantaneous velocity fields. In the near-wall region of this flow, the feature as usually reported in Newtonian fluid wall turbulence was observed and dosed water acts as a promoter of turbulence, which destabilize the flow of the viscoelastic fluid. On the other hand, away from the wall the feature is the one usually observed in drag-reduced flow and dosed water acts as a passive scalar because the mean concentration of dosed water is too small to destabilize the viscoelastic flow.","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114718385","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"MODIFICATIONS OF THE SHEAR LAYER DOWNSTREAM A BACKWARD FACING STEP BY DIELECTRIC BARRIER DISCHARGE PLASMA ACTUATOR","authors":"P. Sujar-Garrido, N. Benard, E. Moreau, J. Bonnet","doi":"10.1615/tsfp8.1930","DOIUrl":"https://doi.org/10.1615/tsfp8.1930","url":null,"abstract":"The present article deals with a free shear layer induced by the separation of a turbulent boundary layer due to wall divergence. The investigated flow configuration is produced by a 30-mm-height backwardfacing-step mounted in a closed-loop wind tunnel. The experimental measurements are performed at 15 m/s , corresponding to a Reynolds number (based on this velocity and the step height) around 3x10. The modifications of the shear layer are achieved with a surface plasma actuator based on a single Dielectric Barrier Discharge (DBD). This actuator produces an electrohydrodynamic force, resulting in a flow called electric wind just upstream the flow separation. The plasma discharge is able to manipulate the first stages of the formation of the free shear layer and consequently to modify the flow dynamics, highlighting the control authority of plasma discharge. Time-averaged and time-resolved measurements techniques are used to investigate the influence of plasma device in two ways. The first one considers the modification of mean reattachment length whereas the second one studies the effect over large-scale structures. INTRODUCTION Free and bounded turbulent shear flows are intensively studied. The turbulent energy balance splits these flows in two generic configurations: wall-bounded and free shear layers. These two types of flow are usually found in the nature and also in a variety of engineering applications. Knowledge of the flow and the ability to control it are fundamental topics in turbulence. This paper is devoted to the characterization of a free shear layer produced by turbulent boundary layer separation and manipulated by a plasma actuator. The massively separated flow is yield by a sudden wall expansion. The sharp step corner is the fixed location where separation occurs and the location where KelvinHelmholtz instability mechanism begins. The whole process is dominated by the structures arising from this instability (Ho & Huerre, 1984). The effects presented here influence not only the mean flow but also these organized large-scale flow structures. In some extend, the particular ‘step’ flow can be compared with the canonical plane mixing layer case. Their characteristics are very similar in the initial region of the free shear layer but further downstream, the growth and evolution of the free shear layer are affected by the presence of the wall downstream in the case of the BFS. A recirculating region forms and feeds continuously the shear layer producing an increase on the overall turbulence (Adams & Johnston, 1988). Another important feature of a backward facing step flow is the unsteady and highly three-dimensional location of the reattachment point. The dynamic of the separated flow is directly linked with this unsteadiness (Driver et al., 1987). The objective of this study is to investigate the ability of plasma actuators as an effective device for modifying (manipulating) the shear layer, with the final objective of being able to c","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116006845","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"PARTICLE-TURBULENCE INTERACTIONS IN THE PRESENCE OF A ROUGH WALL","authors":"G. F. Tay, D. Kuhn, M. Tachie","doi":"10.1615/tsfp8.2030","DOIUrl":"https://doi.org/10.1615/tsfp8.2030","url":null,"abstract":"Experiments were conducted over smooth and rough walls in a low Reynolds number horizontal turbulent channel flow laden with small (64 μm) glass particles. A particle image velocimetry technique was used to measure velocities of both the carrier fluid and particles. Various turbulent characteristics were examined to investigate the impact of wall roughness on the particle-turbulence interactions. The results show that particles increased the turbulent intensities near the wall, and reduced them in the outer layer, but these effects were dampened for the rough wall. On the contrary, particles increased the peak value of the Reynolds shear stress in the presence of the rough wall when compared to the unladen flow. Particle velocity fluctuation intensities matched those of the unladen fluid for the smooth wall, but the peak velocity fluctuation intensities were enhanced in the presence of wall roughness due to particle-wall collisions. The effect is larger for the streamwise velocity fluctuation intensity than the wall-normal velocity fluctuation intensity. The present results indicate that the particle motion is more responsive to the presence of the rough wall than the particle-laden fluid. INTRODUCTION Turbulent flows laden with particles are common in many engineering applications. Examples include fluidized beds, pneumatic conveying and pollution control systems. Understanding these flows as well as developing their model representations demands knowledge of the interaction between particles and fluid turbulence. It has been suggested that depending on the size, density ratio and particulate phase loading, the interaction may lead to modification of the fluid turbulence level. The type of interaction between the particles and fluid is described by the particle volume fraction, Φv, defined as the volume occupied by the particles per unit volume of the particlefluid mixture. For dilute loadings (Φv < 10), particles act as passive tracers, and the particle-fluid interaction is described as one-way coupling. For intermediate loadings (10 < Φv < 10), particles do not only respond to the fluid motion but also modulate the fluid turbulence level. This type of interaction called two-way coupling is the subject of numerous previous experimental and numerical investigations aimed at quantifying the exact impact of particles on turbulence. Tests conducted in channels (Maeda et al. 1980; Tsuji et al. 1984; Liljegren and Vlachos 1990; Kulick et al. 1994; Kiga and Pan 2002; Rani et al. 2004) and boundary layers (Rashidi et al. 1990; Best et al. 1997; Kaftori et al. 1998; Righetti and Romano 2004) by far have produced conflicting results regarding the effects of particles on the fluid mean and turbulent characteristics. Some studies indicate that the carrier fluid mean velocity is enhanced compared to the unladen flow (Maeda et al. 1980; Hagiwara et al. 2002; Righetti and Romano 2004), while others reported the mean velocity to be reduced (Best et al. 1997; K","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117114605","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"UPSTREAM TURBULENCE EFFECTS IN THE SPATIO-TEMPORAL CHARACTERISTICS OF A MODEL A-PILLAR VORTEX","authors":"Faisal Affejee, C. Sicot, R. Perrin, J. Borée","doi":"10.1615/tsfp8.710","DOIUrl":"https://doi.org/10.1615/tsfp8.710","url":null,"abstract":"Conical vortices generated over surfaces having a swept angle with the incidence wind are found in a large class of practical applications. The study presented in this paper is related to the aerodynamic and aero-acoustic of passenger vehicles. More particularly, we focus on the Apillar vortex, arising on the corner edge, between the windshield and the front side window. The incoming flow fields encountered by passenger cars is highly turbulent due to the natural wind or other road traffic. The goal of the paper is then twofold: (i) educe the spatial and temporal characteristics of the A-pillar conical vortex, (ii) investigate the influence of a turbulent stream on these characteristics. For that purpose, a database of simultaneous stereoscopic HSPIV and fluctuating wall pressure measurements was compiled. A spectral analysis of the fluctuating pressure under the vortex is used to analyze the link between the unsteady aerodynamics and the wall pressure field. It has been observed a significant amplification of the meandering of the structure highlighting the high receptivity of this structure to perturbations generated by external turbulence. Introduction Conical vortices generated over surfaces having a swept angle with the incidence wind are found in a particularly large class of practical applications as aerodynamics (delta-wings), civil engineering and transport engineering. The study presented in this paper has a strong link with the aerodynamic and aero-acoustic of passenger vehicles. More particularly, we focus on the A-pillar vortex, arising on the corner edge, between the windshield and the front side window. Previous studies (Alam et al.,2003) have shown that the fluctuating pressures in the A-pillar region of a passenger car are the primary source of ”in cabin” aerodynamic noise. Indeed, the wall stresses induced by the A-pillar vortex are sufficient to make the front side window vibrate and generate noise disturbances inside the car (Levy and al., 2013). The particularity of these A-pillar structures is their strong interaction with the lateral wall of the car. This differs, for example, from delta-wings leading edge vortices at high angle of attack. A mirror image can be used to qualitatively understand the mean downstream evolution of these structures of concentrated vorticity that shift to the roof when traveling toward the back of the car (Hucho 1998). Most of the work related to these typical structures has been experimental and led in wind tunnel in flows with low levels of free stream turbulence (FST). However, incoming flow fields encountered by passenger car are highly turbulent due to the natural wind or other road traffic. This study is then more focused on the effects of freestream turbulence on this conical vortex structure. Effects of FST on bluff body aerodynamic have been studied for a long time. Bearman and Morel (1983) described three basic mechanisms by which FST and the mean flow over bluff bodies interact: acceler","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"104 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124033691","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"ON GEOMETRICALLY SELF-SIMILAR MODES IN WALL-BOUNDED TURBULENT FLOWS","authors":"R. Moarref, Ati S. Sharma, J. Tropp, B. McKeon","doi":"10.1615/tsfp8.1280","DOIUrl":"https://doi.org/10.1615/tsfp8.1280","url":null,"abstract":"","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129785777","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A NEW INTERMITTENCY TRANSPORT EQUATION FOR BYPASS TRANSITION","authors":"E. Juntasaro, K. Ngiamsoongnirn, V. Juntasaro","doi":"10.1615/tsfp8.2240","DOIUrl":"https://doi.org/10.1615/tsfp8.2240","url":null,"abstract":"The new transport equation for intermittency is developed and proposed in this research work, based on the definition of intermittency and the existing transport equations of laminar and turbulent kinetic energy. Its performance is compared with the two existing transition models used in commercial CFD software: L k model and Reθ γ − model, in case of bypass transition. It is found that the proposed model can accurately predict the mean streamwise velocity in the transition zone. For f C , k and u v ′ ′ − , the proposed model has the same performance as the Reθ γ − model. INTRODUCTION During the last decade, there have been two RANSbased transition models used in commercial CFD software: L k model (Walters and Cokljat, 2008) and Reθ γ − model (Langtry and Menter, 2009). The Reθ γ − model was constructed based on correlations obtained from experimental data so that it is reliable only within a range of flow conditions that the experiment is set up to obtain such correlations. The L k model was developed based on basic physical mechanisms and their interaction to capture the flow transition, e.g. redistribution term (process) to model energy transfer from laminar to turbulent stages so that it is more attractive in such a way that it can be applied to a wider range of flow conditions. However, γ , k and L k are strongly related to each other by the definition of γ . Therefore, their transport equations should be developed in an interconnected manner. This research work is aimed to identify the incomplete modeling scheme of the L k model which requires one more transport equation for γ to complete the relationship among γ , k and L k , according to the definition of γ . Finally, the new transport equation for γ will be developed and proposed here. DERIVATION OF A NEW INTERMITTENCY TRANSPORT EQUATION To begin with, γ or the intermittency of laminar-toturbulent flow transition is defined as the fraction of time in which the flow is turbulent at a fixed point (Schneider, 1995). According to its definition, γ can be formulated as follows:","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"31 4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127537529","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"THREE-DIMENSIONAL SPECTRAL ANALYSIS OF AN AXISYMMETRIC SEPARATING/REATTACHING FLOW","authors":"R. Pain, P. Weiss, S. Deck","doi":"10.1615/tsfp8.100","DOIUrl":"https://doi.org/10.1615/tsfp8.100","url":null,"abstract":"The numerical investigation of a high Reynolds number compressible separating-reattaching flow around a simplified space launcher afterbody is carried out using Zonal Detached Eddy Simulation (ZDES). The geometry consists of a cylinder extended by another cylinder of smaller diameter. Spectral analysis of the three-dimensional unsteady pressure field is carried out by means of a discrete Fourier approach as well as a dynamic mode investigation. First, the visualisation of the Power Spectral Density (PSD) around the geometry evidences that high fluctuating energy areas are located on the second half of the emerging cylinder on the skin of the same geometry. It is revealed that such high PSD areas are associated with low frequencies which is often the case for separated flows. The analysis of the dynamic mode associated with the vortex shedding Strouhal number StD = f D U∞ = 0.18 exhibits a large scale doublehelical organisation which is consistent with results from other investigations in the literature using alternative postprocessing tools at lower Reynolds numbers.","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127172620","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"DYNAMICAL MODELING OF LARGE SCALE COHERENT STRUCTURES IN THE WAKE OF A WALL MOUNTED FINITE CYLINDER","authors":"Z. Hosseini, Zixiang Chen, R. Martinuzzi","doi":"10.1615/tsfp8.1990","DOIUrl":"https://doi.org/10.1615/tsfp8.1990","url":null,"abstract":"The Extended Proper Orthogonal Decomposition (EPOD) was used to estimate the coherent structures in the wake of a wall mounted finite cylinder from the surface fluctuating pressure. To show the surface pressure is actually a good indicator, the method was first applied to the Large Eddy Simulation (LES) results, from which the instantaneous velocity and pressure data were available in the whole domain. Subsequently, the method was applied to planar Particle Image Velocimetry (PIV) measurements for which only the pressure at discrete points at the cylinder side faces were taken. Even though a part of the correlation is lost due to the experimental limitations, the amplitude modulations and base flow variations around the average limit cycle were recovered and great improvements were achieved over the traditional phase averaging approach.","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129050420","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}