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

{"title":"A PARAMETRIZED NON-EQUILIBRIUM WALL-MODEL FOR LARGE-EDDY SIMULATIONS","authors":"S. Hickel, E. Touber, J. Bodart, J. Larsson","doi":"10.13140/2.1.1281.6324","DOIUrl":"https://doi.org/10.13140/2.1.1281.6324","url":null,"abstract":"Wall-models are essential for enabling large-eddy simulations (LESs) of realistic problems at high Reynolds numbers. The present study is focused on approaches that directly model the wall shear stress, specifically on filling the gap between models based on wall-normal ordinary differential equations (ODEs) that assume equilibrium and models based on full partial differential equations (PDEs) that do not. We develop ideas for how to incorporate non-equilibrium effects (most importantly, strong pressure-gradient effects) in the wall-model while still solving only wall-normal ODEs. We test these ideas using two reference databases: an adverse pressure-gradient turbulent boundary-layer and a shock/boundary-layer interaction problem, both of which lead to separation and re-attachment of the turbulent boundary layer.","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133747548","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":"TURBULENT MIXING IN A PRECESSING SPHERE","authors":"S. Goto, M. Shimizu, G. Kawahara","doi":"10.1063/1.4901449","DOIUrl":"https://doi.org/10.1063/1.4901449","url":null,"abstract":"By numerically simulating turbulent flows at high Reynolds numbers in a precessing sphere, we propose a method to enhance the mixing of a fluid confined within a smooth cavity by its rotational motion alone. To precisely evaluate the mixing efficiency, we extend the quantification method proposed by Danckwerts [“The definition and measurement of some characteristics of mixtures,” Appl. Sci. Res. A 3, 279–296 (1952)] to the case in which only a finite number of fluid particle trajectories can be known. Our accurate numerical tracking of fluid particles in the flow, which is controlled by the Reynolds number (an indicator of the spin rate) and the Poincare number (the precession rate), shows the following results. First, the mixing process on the time scale normalized by the spin period is independent of the Reynolds number as long as it is high enough for the flow to be developed turbulence. Second, fastest mixing is achieved under weak precession (Poincare number ≈0.1); in such cases, perfect mixing requi...","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"139 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115969204","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":"SLIP VELOCITY OF RIGID FIBERS IN A TURBULENT CHANNEL FLOW","authors":"Lihao Zhao, C. Marchioli, H. Andersson","doi":"10.1063/1.4881942","DOIUrl":"https://doi.org/10.1063/1.4881942","url":null,"abstract":"In this study, the slip velocity between rigid fibers and a viscous carrier fluid is investigated for the reference case of turbulent channel flow. The statistical moments of the slip velocity are evaluated modelling fibers as prolate spheroids with Stokes number, St, ranging from 1 to 100 and aspect ratio, λ, ranging from 3 to 50. Statistics are compared one-to-one with those obtained for spherical particles (λ = 1) to highlight effects due to fiber elongation. Comparison is also made at different Reynolds numbers (Reτ =150, 180, and 300 based on the fluid shear velocity) to discuss effects due to an increase of turbulent fluctuations. Results show that elongation has a quantitative effect on slip velocity statistics, particularly evident for fibers with small St. As St increases, differences due to the aspect ratio tend to vanish and the relative translational motion between individual fibers and surrounding fluid is controlled by fiber inertia through preferential concentration. A clear manifestation o...","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128994845","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":"DECAY OF THE TURBULENT WAKE FROM THE SUPERSONIC MICRO RAMP","authors":"Zhengzhong Sun, B. Oudheusden, F. Schrijer, F. Scarano","doi":"10.1615/tsfp8.2000","DOIUrl":"https://doi.org/10.1615/tsfp8.2000","url":null,"abstract":"The wake resulting from two micro ramps operating in a supersonic boundary layer at Ma = 2:0 is investigated by means of PIV. Two micro ramps are investigated with height of 60% and 80% of the undisturbed boundary layer with thickness of 5.2 mm. The measurement domain encompasses the range from 10 to 32 ramp heights downstream of the device. The decay properties are evaluated in terms of time-averaged and root-mean-square (RMS) statistics. In the time-averaged flow field, the recovery of the imparted momentum deficit and the decay of upwash motion are revealed. The RMS fluctuations of the velocity components exhibit strong anisotropy at upstream locations but develop into a more isotropic regime downstream. The Kelvin-Helmholtz (K-H) instability at the upper shear layer further develops with the onset of vortex pairing. The wavelength evolution is estimated using statistic-based spatial auto-correlation. A marked transition with the wavelength nearly doubled is observed across the pairing regime.","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123593549","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":"DYNAMICS OF A TURBULENT BOUNDARY LAYER OVER CUBICAL ROUGHNESS ELEMENTS: INSIGHT FROM PIV MEASUREMENTS AND POD ANALYSIS","authors":"L. Perret, Cédric Rivet","doi":"10.1615/tsfp8.1850","DOIUrl":"https://doi.org/10.1615/tsfp8.1850","url":null,"abstract":"The dynamics of the turbulent boundary layer developing over a cube array is analysed using stereoscopic PIV measurements performed in an atmospheric wind tunnel. The longitudinal component u of the velocity is analysed via the snapshot POD. It is first demonstrated that the first POD mode of u corresponds to large-scale elongated coherent structures of lowor high-speed which are non-negligible contributors to the shear-stress and the turbulent kinetic energy. Their relationship with the smaller scales of the flow is investigated via the computation of oneor two-point third order statistics and is shown to be of non-linear nature. INTRODUCTION During the past few years, very-large-scale motions (VLSMs) in turbulent boundary layers over smooth-walls have received renewed attention from the research community. Both numerical and experimental studies have highlighted their influence on the near-wall turbulence and their contribution to the kinetic energy and Reynolds shear-stress in different type of wall-bounded flows such as pipe flows (Monty et al., 2007), channel flows (del Alamo & Jimenez, 2003), laboratory boundary layers (Marusic & Hutchins, 2008) and atmospheric boundary layers (Guala et al., 2011). Common features of the VLSMs found in wall-bounded flows are that they consist in elongated lowand high-speed regions (Hutchins & Marusic, 2007), the length of which scales with outer-length variable (δ ) and can reach several times δ (Guala et al., 2011), they populate the log and outer layer, they are animated by a meandering motion in the horizontal plane (Hutchins & Marusic, 2007) and interact with near-wall turbulence through an amplitudemodulation mechanism (Mathis et al., 2009). The finding of this last characteristics relies on the clear spectral separation between large-scale motions and the near-wall turbulence found in high Reynolds number flows (Guala et al., 2011; Mathis et al., 2009). At the same time, attention has been devoted to the structure of boundary layer flows developing over rough walls, at laboratory scales (see Jimenez 2004 for a review) or in the framework of atmospheric flows over urban or vegetation canopies (Finnigan et al., 2009; Inagaki & Kanda, 2010; Takimoto et al., 2011), demonstrating similarities between flows over smooth and rough wall. In particular, the presence of streaky patterns of lowand high-speed regions, of ejection and sweep motions associated to the hairpin model and the organization of hairpin vortices in packets have been evidenced. Recently, Inagaki & Kanda (2010) showed the presence in the atmospheric flow developing over an array of cubes of very-large-scale elongated lowspeed regions, with some sub-structures included in these streaks. These structures, educed by filtering in the spanwise direction the time-series from a spanwise array of 15 sonic anemometers, share some common features with the above mentionned VLSMs evidenced in smooth wall flows and support the observations of Drobinski et","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"93 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121119879","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":"STIRRING AND MIXING BY GRID-GENERATED TURBULENCE IN THE PRESENCE OF A MEAN SCALAR GRADIENT","authors":"S. Laizet, J. Vassilicos","doi":"10.1299/JSMEICJWSF.2013.4._1024-1_","DOIUrl":"https://doi.org/10.1299/JSMEICJWSF.2013.4._1024-1_","url":null,"abstract":"The stirring and mixing of a passive scalar by gridgenerated turbulence in the presence of a mean scalar gradient is studied in three dimensions by DNS (Direct Numerical Simulation). Using top-end high fidelity computer simulations, we calculate and compare the effects of various fractal and regular grids on scalar transfer and turbulent diffusion efficiencies. We demonstrate the existence of a new mechanism present in turbulent flows generated by multiscale/fractal objects and which has its origin in the multiscale/fractal space-scale structure of such turbulent flow generators. As a result of this space-scale unfolding (SSU) mechanism, fractal grids can enhance scalar transfer and turbulent diffusion by one order of magnitude while at the same time reduce pressure drop by half. The presence of this SSU mechanism when turbulence is generated by fractal grids means that the spatial distribution of length-scales unfolds onto the streamwise extent of the flow and gives rise to a variety of wake-meeting distances downstream. This SSU mechanism must be playing a decisive role in environmental, atmospheric, ocean and river transport processes wherever turbulence originates from multiscale/fractal objects such as trees, forests, mountains, rocky river beds and coral reefs. It also ushers in the new concept of fractal design of turbulence which may hold the power of setting entirely new mixing and cooling industrial standards.","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"29 10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132277781","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":"DIRECT NUMERICAL SIMULATION OF TURBULENT FLOW WITH SUPERCRITICAL FLUID IN A HEATED PIPE","authors":"H. Nemati, A. Patel, B. Boersma, R. Pecnik","doi":"10.1615/tsfp8.770","DOIUrl":"https://doi.org/10.1615/tsfp8.770","url":null,"abstract":"This work investigates turbulent heat transfer to a pipe flow with a fluid close to its vapour-liquid critical point. The flow is simulated using Direct Numerical Simulations (DNS) of the anelastic Navier-Stokes equations at a Reynolds number of Ret = 360, based on the friction velocity ut at the inlet and the diameter of the pipe. Turbulent statistics for two cases with forced and mixed convection are discussed. A decrease in turbulent kinetic energy is observed for both cases due to flow acceleration and buoyancy effects. Furthermore it is observed that the correlation between turbulent heat flux and Reynolds stresses is lower than in subcritical flows.","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"65 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131403698","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":"DYNAMICS OF ELASTO-INERTIAL TURBULENCE IN FLOWS WITH POLYMER ADDITIVES","authors":"V. Terrapon, Y. Dubief, J. Soria","doi":"10.1615/tsfp8.2150","DOIUrl":"https://doi.org/10.1615/tsfp8.2150","url":null,"abstract":"The dynamics of elasto-inertial turbulence is investigated numerically from the perspective of the coupling between polymer dynamics and flow structures. In particular, direct numerical simulations of channel flow with Reynolds numbers ranging from 1000 to 6000 are used to study the formation and dynamics of elastic instabilities and their effects on the flow. Based on the splitting of the pressure into inertial and polymeric contributions, it is shown that the trains of cylindrical structures around sheets of high polymer extension that are characteristics to elasto-inertial turbulence are mostly driven by polymeric contributions. INTRODUCTION Polymer additives are known for producing upward of 80% drag reduction in turbulent wall-bounded flows through strong alteration and reduction of turbulent activity (White & Mungal, 2008). The changes in flow dynamics induced by polymers do not lead to flow relaminarization but, at most, to a universal asymptotic state called maximum drag reduction (MDR, Virk et al. 1970). At the same time, polymer additives have also been shown to promote transition to turbulence (Hoyt, 1977), or even lead to a chaotic flow at very low Reynolds number as in elastic turbulence (Groisman & Steinberg, 2000). These seemingly contradicting effects of polymer additives can be explained by the interaction between elastic instabilities and the flow’s inertia characterizing elastoinertial turbulence, hereafter referred to as EIT (Samanta et al., 2012; Dubief et al., 2013). EIT is a state of smallscale turbulence that exists by either creating its own extensional flow patterns or by exploiting extensional flow topologies. EIT provides answers to phenomena that current understanding of MDR cannot, such as the absence of log-law in finite-Reynolds numbers MDR flows (White et al., 2012), and the phenomenon of early turbulence. Moreover, it supports De Gennes (1990)’s picture that drag reduction derives from two-way energy transfers between turbulent kinetic energy of the flow and elastic energy of polymers at small scales, resulting in an overall modification of the turbulence energy cascade at high Reynolds numbers. As shown by the viscoelastic pipe experiment of Samanta et al. (2012), an elastic instability can occur at a Reynolds number smaller than the transition in Newtonian pipe flow if the polymer concentration and Weissenberg number are sufficiently large. Moreover, it was observed that the measured friction factor then follows the characteristic MDR friction law. These findings were also confirmed by direct numerical simulations as shown in Figure 1 (Dubief et al., 2013). The analysis of these simulations showed that thin sheets of locally high polymer stretch, tilted upwards and elongated in the flow direction, create trains of spanwise cylindrical structures of alternating sign, as shown in Figure 2. This feature of EIT disappears when the flow is too turbulent or the polymer solution not elastic enough, which led to the hy","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"35 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126673168","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":"TURBULENCE AND SCALAR TRANSPORT IN HEATED BOUNDARY LAYERS WITH VISCOSITY STRATIFICATION","authors":"Jin Lee, Seo Yoon Jung, H. Sung, T. Zaki","doi":"10.1615/tsfp8.260","DOIUrl":"https://doi.org/10.1615/tsfp8.260","url":null,"abstract":"","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"116 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124623489","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":"VOLUMETRIC MEASUREMENTS BY TOMOGRAPHIC PIV OF GRID GENERATED TURBULENCE IN AN OPEN CHANNEL FLOW","authors":"T. Earl, L. Thomas, S. Cochard, Riadh Ben-Salah, B. Tremblais, L. David","doi":"10.1615/tsfp8.2110","DOIUrl":"https://doi.org/10.1615/tsfp8.2110","url":null,"abstract":"This paper investigates the energy dissipation rate behind two combinations of trash racks (or meshes) in an open channel flow. Five trash rack assemblies divided the flume into four identical pools in the downstream direction. The global characteristics of the flow were compared with Tomo-PIV measurements that were taken in the water column of the flow. From the Tomo-PIV measurements, the instantaneous structures in the flow were visualised and the decay of turbulent kinetic energy and energy dissipation analysed.","PeriodicalId":206337,"journal":{"name":"Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124035624","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}