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

{"title":"OFFSET HEIGHT EFFECTS ON TURBULENT CHARACTERISTICS OF SUBMERGED JETS","authors":"M. S. Rahman, G. F. Tay, M. Tachie","doi":"10.1615/tsfp10.140","DOIUrl":"https://doi.org/10.1615/tsfp10.140","url":null,"abstract":"Experimental study of turbulent characteristics of submerged jet near the free surface was carried out at four offset height ratios of 1, 2, 3 and 4. The Reynolds number based on jet exit velocity and nozzle width was 5500. A particle image velocimetry system was used for the velocity measurement. The jet attachment length increased with the offset height. The results showed that the free surface affected the maximum velocity decay and jet spread for the shallower jets. The surface mean velocity and Reynolds normal stresses were quantified and dramatic reduction of surface-normal Reynolds normal stress than its streamwise component was observed in the interaction region. Joint probability density functions were used to investigate the contribution of the turbulent events to Reynolds shear stress. INTRODUCTION Turbulent jets discharged in the vicinity of a free surface are often referred to as submerged jets. Submerged jets have various practical applications which include disposal of industrial effluent into shallow streams, water purification, and in the remote sensing of moving ships. Understanding the mixing characteristics and turbulent structures in submerged jets is important to the design of engineering devices. A schematic diagram of a submerged jet is shown in figure 1. The nozzle of width, d is located near the free surface. The offset height of the center of the nozzle from the free surface is denoted by h. The origin of the Cartesian coordinate system adopted in the present study is located at the center of the nozzle in the jet exit plane; x and y indicate the streamwise and surface-normal direction respectively, U and V indicate the streamwise and surface-normal mean velocities respectively, u and v are the streamwise and surface-normal fluctuating velocities respectively; and Uj is the jet exit velocity. The jet attaches to the free surface upon discharge at the attachment point, xr. The flow field of a submerged jet can be divided into two regions: recirculation region and surface jet region. In the recirculation region, characteristic negative U is found between the upper edge of the jet and the free surface. The streamwise extent of the recirculation region is measured from the nozzle exit to the attachment point and is often reffered to as attachment length. After the recirculation region, surface jet region starts. In the surface jet region, positive U appears at the free surface. One of the salient characteristics of a submerged jet is that the location of local maxumum streamwise mean velocity, Um deviates from the nozzle centerline with the jet development downstream and moves towards the free surface (Anthony and Willmarth, 1992). The dashed line passing through the location of Um as shown in the figure demarcates the two shear layers of the jet. The upper and lower portion of this dashed line is reffered to as upper and lower shear layer, respectively. y0.5 and y0.5 are the distances of the location of 0.5Um measured from","PeriodicalId":266791,"journal":{"name":"Proceeding of Tenth International Symposium on Turbulence and Shear Flow Phenomena","volume":"14 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":"115999357","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":"FREE-STREAM TURBULENCE AND ITS INFLUENCE ON BOUNDARY-LAYER TRANSITION","authors":"J. Fransson","doi":"10.1615/tsfp10.1260","DOIUrl":"https://doi.org/10.1615/tsfp10.1260","url":null,"abstract":"Free-stream turbulence (FST) gives, undoubtedly, rise to the most complicated boundary-layer transition-toturbulence scenario. The reason for the complexity is that the boundary layer thickness gro ...","PeriodicalId":266791,"journal":{"name":"Proceeding of Tenth International Symposium on Turbulence and Shear Flow Phenomena","volume":"21 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":"126655898","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 the accuracy and robustness of implicit LES / under-resolved DNS approaches based on spectral element methods","authors":"R. Moura, J. Peiró, S. Sherwin","doi":"10.1615/tsfp10.560","DOIUrl":"https://doi.org/10.1615/tsfp10.560","url":null,"abstract":"We present a study on the suitability of under-resolved DNS (uDNS) – also called implicit LES (iLES) – approaches based on spectral element methods (SEM), with emphasis on high-order continuous and discontinuous Galerkin (i.e. CG and DG) schemes. Broadly speaking, these are model-free eddy-resolving approaches to turbulence which solve the governing equations in unfiltered form and rely on numerical stabilization techniques for small-scale regularization. Model problems in 1D, 2D and 3D are used in the assessment of solution quality and numerical stability. A rationale for the excellent potential of these methods for transitional and turbulent flows is offered on the basis of linear dispersion-diffusion analysis.","PeriodicalId":266791,"journal":{"name":"Proceeding of Tenth 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":"125739123","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":"THE EFFECT OF THE BACKING CAVITY ON THE CONTROL OF THE TURBULENT BOUNDARY LAYER BY THE APPLICATION OF A CAVITY ARRAY","authors":"A. Silvestri, F. Ghanadi, M. Arjomandi, B. Cazzolato, A. Zander","doi":"10.1615/tsfp10.510","DOIUrl":"https://doi.org/10.1615/tsfp10.510","url":null,"abstract":"The results presented in this paper provide an insight into the effect of a cavity array on the turbulence production within a turbulent boundary layer. In the present study, the turbulent energy production within a fully developed turbulent boundary layer has been reduced using a flushed-surface cavity array underneath a flat plate coupled with an acoustic actuator. The size of the holes in the cavity array were selected to be comparable with the dimensions of the expected coherent structures, based on the friction velocity. Experimental measurements were taken in a wind tunnel at a number of locations along the array in the streamwise direction and at a variety of acoustic frequencies generated by the acoustic actuator. A maximum turbulence intensity and sweep intensity reduction of 11% and 10% respectively occurred at Reθ = 3.771 × 10 in the logarithmic region of the boundary layer when no drive frequency was provided. From this investigation it has been shown that the drive frequency of the acoustic actuator has no effect on the turbulence reduction by the cavity array. Instead the physical parameters of the array, including the number and diameter of the cavities in the array have a much more","PeriodicalId":266791,"journal":{"name":"Proceeding of Tenth International Symposium on Turbulence and Shear Flow Phenomena","volume":"47 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":"130863017","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":"Transition mechanism in a shock wave boundary layer interaction","authors":"Moussa Diop, S. Piponniau, P. Dupont","doi":"10.1615/tsfp10.980","DOIUrl":"https://doi.org/10.1615/tsfp10.980","url":null,"abstract":"","PeriodicalId":266791,"journal":{"name":"Proceeding of Tenth International Symposium on Turbulence and Shear Flow Phenomena","volume":"23 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":"130484251","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 STRUCTURE LEADING TO UNSTEADY UPSTREAM SEPARATION IN COUETTE FLOW WITH FORWARD-FACING STEP","authors":"Yohei Morinishi, Shohei Kubota, Shinji Tamano, Toru Yamada","doi":"10.1615/tsfp10.360","DOIUrl":"https://doi.org/10.1615/tsfp10.360","url":null,"abstract":"","PeriodicalId":266791,"journal":{"name":"Proceeding of Tenth International Symposium on Turbulence and Shear Flow Phenomena","volume":"56 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":"127618260","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":"Examination of changes to the spatial structure of turbulent boundary layers due to surface-wave forcing using POD","authors":"Owen J. H. Williams, M. Wong","doi":"10.1615/tsfp10.870","DOIUrl":"https://doi.org/10.1615/tsfp10.870","url":null,"abstract":"Changes to the spatial structure of turbulent boundary layers due to the presence free-surface waves are investigated using Partial orthogonal decomposition (POD). For the current study, the wavelength of the surface waves is approximately three times the boundary layer thickness. Large particle image velocimetry (PIV) datasets are used to obtain a wide range of converged POD modes, both with and without surface wave forcing, allowing the comparison of spatial structure. A hierarchical series of inclined lowand highmomentum structures that contribute to negative turbulent shear stress, and are reminiscent of hairpin packets, are observed near to the wall in the unperturbed case. These structures are observed to be highly disrupted by the depth-varying wave perturbation, with fewer and weaker inclined near-wall structures observed in the later case. Perhaps most significantly, all of the remaining inclined attached structures have streamwise lengthscales less than the wavelength of the disturbance and have increased angle of inclination. These results suggest that surface waves significantly alter the structure of large-scale turbulent packets with streamwise lengthscales greater or equal to the wavelength but have less effect on smaller scale productive motions.","PeriodicalId":266791,"journal":{"name":"Proceeding of Tenth International Symposium on Turbulence and Shear Flow Phenomena","volume":"34 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":"115285733","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":"Effects of vortex-induced velocity on the wake of a synthetic jet issuing into a turbulent boundary layer","authors":"T. Berk, G. Gomit, B. Ganapathisubramani","doi":"10.1615/tsfp10.440","DOIUrl":"https://doi.org/10.1615/tsfp10.440","url":null,"abstract":"A synthetic jet issued in a cross flow creates a momentum deficit in the cross flow downstream of the jet. In the literature, this deficit is ascribed to viscous blockage by the jet and the up wash of low-momentum fluid caused by the vortical structures of the jet. This paper proposes and quantifies a third effect contributing to the momentum deficit: a velocity induced by the vortical structures in the direction opposite to the cross flow. A reconstruction technique – quantifying the vortex-induced velocity – is developed to determine the momentum deficit caused by the proposed effect. This is applied to a test case of a rectangular synthetic jet (AR = 13, St = 0.5, r = 0.88) issuing into a turbulent boundary layer (Reτ = 1220, U∞ = 10 m/s, δ = 45 mm). The shape of the created vortical structures is reconstructed using a combination of planar(two-dimensional two-component) PIV in the streamwise– wall-normal plane and stereo(two-dimensional three-component) PIV in the spanwise–wall-normal plane. The reconstructed shape consists of overlapping clockwiseand counterclockwise hairpins. With this (constant) shape known, the distribution of hairpins can be determined using the spanwise-vorticity field only. From this distribution of vortical structures the induced velocity is calculated using Biot-Savart’s law. Qualitatively the induced velocity components are very similar to the equivalent measured velocity components. The streamwise momentum flux deficit per unit width at the centerline is calculated for both the induced and the measured case. After some start-up behaviour the momentum deficit for both cases becomes relatively constant. In this constant regime (x/δ > 1) the momentum deficit induced by the vortical structures accounts for 90% of the measured momentum deficit. It is reasoned that the other 10% is most likely to be caused by an increase in skin friction resulting from the up wash of low-momentum fluid (and consequential down wash of high-momentum fluid). INTRODUCTION Synthetic jets in cross flow are widely used in applications such as mixing enhancement (M’Closkey et al., 2002; Sau & Mahesh, 2008), control of turbulence (Rathnasingham & Breuer, 2003) or separation control (Dandois et al., 2007). The interaction of a synthetic jet with a cross flow leads to a momentum deficit in the cross flow downstream of the jet, causing an increase in drag. For most applications minimization of this momentum deficit is of importance for the efficiency of the pursued goal. In order to minimize it, the origin of the momentum deficit needs to be understood. In the literature, the momentum deficit is often referred to as blockage (see for example Lardeau & Leschziner (2011)), or as caused by vortex induced up wash of low-momentum fluid near the wall (see for example Rathnasingham & Breuer (2003)). However, these were qualitative descriptions and do not quantify the momentum deficit in any detail. This paper proposes a third origin and quantifies its mome","PeriodicalId":266791,"journal":{"name":"Proceeding of Tenth 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":"123924485","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":"Stochastic Modeling of Passive Scalar Transport in Turbulent Channel Flows at High Schmidt Numbers","authors":"M. Klein, H. Schmidt","doi":"10.1615/tsfp10.90","DOIUrl":"https://doi.org/10.1615/tsfp10.90","url":null,"abstract":"High-Schmidt number flow simulations are challenging since the flow has to be resolved down to the Batchelor scale, which yields high resolution requirements. In order to close the gap between the flow regime of applications and that reachable by numerical simulations, we utilize a stochastic modeling approach, the so-called OneDimensional Turbulence (ODT) model. In the present study, ODT is used as stand-alone tool to investigate the turbulent transport of a passive scalar for Schmidt numbers 1 ≤ Sc ≤ 5000 in incompressible, fully-developed turbulent channel flows for Reynolds numbers Reτ ≤ 2000. The applicability of ODT is assessed by comparing the scalar mean and the root mean square fluctuations to those of reference Direct Numerical Simulations (DNS) and Large-Eddy Simulations (LES) up to Sc = 400. Good qualitative but also quantitative agreement is observed between DNS, LES, and ODT, but ODT underestimates the mean scalar concentration in the bulk by a factor of ≈ 3/4. Otherwise, ODT exhibits the correct boundary layer structure and yields the von Kármán constant for the scalar as κθ = 0.23, which corresponds well to the available reference DNS/LES. ODT is then used to simulate the scalar mass transfer coefficient K+ up to very high Schmidt numbers. The power law K ODT ∝ Sc −0.651 is obtained for Sc > 100 where it is also independent of the Reynolds number. This corresponds to the reference laboratory measurements and DNS/LES, which obey K lab ∝ Sc −0.704. The present study shows that ODT can be a versatile tool for robust and accurate modeling of the turbulent scalar transport up to very high Schmidt and Reynolds numbers.","PeriodicalId":266791,"journal":{"name":"Proceeding of Tenth International Symposium on Turbulence and Shear Flow Phenomena","volume":"354 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":"122995163","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":"Laser Doppler Velocimetry Measurements of A Turbulent Boundary Layer Flow over Sprayed Superhydrophobic Surfaces","authors":"J. Gose, Kevin Golovin, J. Barros, M. Schultz, A. Tuteja, M. Perlin, S. Ceccio","doi":"10.1615/tsfp10.40","DOIUrl":"https://doi.org/10.1615/tsfp10.40","url":null,"abstract":"Measurements of near-zero pressure gradient turbulent boundary layer (TBL) flow over several superhydrophobic surfaces (SHSs) are presented and compared to those for a hydraulically smooth baseline. The surfaces were developed at the University of Michigan as part of an ongoing research thrust to investigate the feasibility of SHSs for skin-friction drag reduction in turbulent flow. The SHSs were previously evaluated in fullydeveloped turbulent channel flow and have been shown to provide meaningful drag reduction. The TBL experiments were conducted at the U.S. Naval Academy in a water tunnel with a test section 2.0 m (L) × 0.2 m (W) × 0.1 m (H). The free-stream speed was set to 1.25 ms, nominally, which corresponded to a friction Reynolds number, Reτ, of 1,600. The TBL was tripped at the test section inlet with a 0.8 mm diameter wire. The upper and side walls provided optical access, while the lower wall was either the smooth baseline or a spray coated SHS. The velocity measurements were obtained with a two-component Laser Doppler Velocimeter (LDV) and custom-designed beam displacer operated in coincidence mode. The LDV probe volume diameter was 45 μm (approx. two wallunits). The measurements were recorded 1.5 m downstream of the trip. When the measured quantities were normalized using inner variables, the results indicated a significant reduction in the near wall viscous and total stresses. Increased stresses were also measured in the overlap layer when compared to the smooth wall. Nevertheless, consideration of the total stress and a log layer with a wake analysis shows drag reduction of -11 to 36% for the SHS analyzed. INTRODUCTION Nature has provided an exhaustive source of evolutionary functional materials to be mimicked for everyday applications (Jung & Bhushan, 2010). One notable case relevant to the marine environment is the lotus leaf which is known for its self-cleaning properties and resistance to wetting (Neinhuis & Barthlott, 1997).","PeriodicalId":266791,"journal":{"name":"Proceeding of Tenth International Symposium on Turbulence and Shear Flow Phenomena","volume":"44 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":"124816859","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}