Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session L15: Turbulent Boundary Layers: Curvature and Pressure Gradients II |
Hide Abstracts |
Chair: Ralph Volino, United States Naval Academy Room: 310 |
Monday, November 25, 2019 1:45PM - 1:58PM |
L15.00001: Non-Equilibrium Boundary Layer Development in Response to Changing Pressure Gradients Ralph Volino Experiments were conducted in non-equilibrium turbulent boundary layers on a smooth flat wall. The test section included a zero pressure gradient (ZPG) development region, followed by a favorable pressure gradient (FPG) region with constant acceleration parameter $K=(\nu/{U_\infty}^2)(dU_\infty/dx)$, a ZPG recovery, and a constant $K$ adverse pressure gradient (APG) region. Eight cases were included with three different inlet velocities and $K$ in the FPG ranging from $0.125\times10^{-6}$ to $2\times10^{-6}$. The $K$ magnitude of the APG in each case was half that of the FPG. Velocity profiles were acquired at 12 streamwise stations using a two component LDV, and PIV was used to document velocity fields at the same stations. The mean velocity and turbulence profiles and correlations were observed to change in response to the changing pressure gradients, and changes in various quantities (e.g. wake strength or $u^\prime v^\prime$ at representative $y^+$) were quantified as functions of streamwise location. Normalizations of streamwise distance were found for the FPG, ZPG, and APG regions that caused the data to collapse, quantifying the non-equilibrium response to the changing pressure gradients. [Preview Abstract] |
Monday, November 25, 2019 1:58PM - 2:11PM |
L15.00002: Spatio-temporal dynamics of pressure-induced turbulent separation bubbles Wen Wu, Charles Meneveau, Rajat Mittal The spatio-temporal dynamics of separation bubbles (SBs) induced to form in a fully-developed turbulent boundary layer over a flat plate are studied via direct numerical simulations. Two different SBs are examined: one induced by a suction-blowing velocity profile on the top boundary and the other, by a suction-only velocity profile. The latter condition allows reattachment to occur without an externally imposed favourable pressure gradient and leads to a SB more representative of those occurring over airfoils and in diffusers. The suction-only SB exhibits a range of clearly distinguishable modes. The high-frequency modes are well characterized by classical frequency scalings for a plane mixing layer and are associated with the formation and shedding of spanwise oriented vortex rollers. The topology associated with the low-frequency motion is revealed by the application of dynamic mode decomposition (DMD) and is shown to be dominated by highly elongated structures in the streamwise direction. The possibility of G\"{o}rtler instability as the underlying mechanism for these structures is explored. [Preview Abstract] |
Monday, November 25, 2019 2:11PM - 2:24PM |
L15.00003: Effects of Adverse Pressure Gradient and Convex Curvature on the Evolution of Turbulence Statistics and Coherent Structures~ . Simeret Genet, Liuyang Ding, Alexander Smits, Marcus Hultmark Here we are interested in developing models and scaling relationships that better characterize non-equilibrium, turbulent, wall-bounded flows. In this study, an axisymmetric body is used to introduce streamwise pressure gradients and streamline curvature to a fully developed turbulent flow in a pipe. This body consists of three sections which are the bow, recovery region and the stern. The flow first sees the bow that creates a favorable pressure gradient. It then passes over the recovery region before meeting the stern that introduces an adverse pressure gradient (APG). Particle Image Velocimetry (PIV) is used to measure the flow field. The evolution of turbulent statistics as well as deformations of coherent structures are quantified in the stern region of the body of revolution. Different sized bodies are used to vary the strengths of the APG. Lastly, results from PIV are compared with data obtained from hot wire measurements at high Reynolds numbers in the Superpipe. [Preview Abstract] |
Monday, November 25, 2019 2:24PM - 2:37PM |
L15.00004: Mean Momentum Balance in Adverse Pressure Gradient Boundary Layers Sylvia Romero, Spencer Zimmerman, Jimmy Phillip, Joseph Klewicki Utilizing Large Eddy Simulation (LES) data from Bobke et al. (2017) the mean momentum equation for a two-dimensional adverse pressure gradient boundary layer (APG BL) will be analyzed in comparison to the channel flow case. The properties of the mean momentum balance (MMB) for a channel flow are well characterized (e.g. see Wei et al. (2005)). Like the channel flow case, the MMB for the two-dimensional zero pressure gradient boundary layer (ZPG BL) is a balance of three terms. Morrill-Winter et al. (2017) transformed the MMB terms of the ZPG BL into a form like the channel flow case. Using the data of Bobke et al. (2017), the present analysis examines whether a similar transformation is applicable to APG flows. The MMB for APG flows is a balance of four terms, unlike the three for the ZPG BL and channel flow. The fourth term, the pressure gradient term, is a negative constant in APG flows, but is a positive constant in channel flows. The change in dominance of the MMB terms will be discussed, as well as the dependence of the balance on the pressure gradient and distance from the wall. Various aspects such as the history effects of the developing pressure gradient and the location where the viscous force loses dominance will also be discussed. [Preview Abstract] |
Monday, November 25, 2019 2:37PM - 2:50PM |
L15.00005: Direct Numerical Simulations of Separated Flow over a Bump Riccardo Balin, Philippe Spalart, Kenneth Jansen A turbulent boundary layer over a Gaussian bump is computed by direct numerical simulation (DNS) of the incompressible Navier-Stokes equations. The two-dimensional bump causes a rapid succession of favorable-to-adverse pressure gradients that can lead to shallow separation on the downstream side, both of which are characteristic of the flow over the flap of an aircraft wing in high-lift configurations. At the inflow, the momentum thickness Reynolds number is approximately 1,000, and the boundary layer thickness is 1/8 of the bump height. Results from DNS are discussed, describing the complex flow physics observed and the effects of variations to the inflow mean profile. Data from this study will be used for the development of lower fidelity turbulence models through data driven approaches. [Preview Abstract] |
Monday, November 25, 2019 2:50PM - 3:03PM |
L15.00006: Validation Experiments for Turbulent Separated Flows over Axisymmetric Afterbodies Samantha Gildersleeve, Christopher L. Rumsey Historically, the flow physics involved with most turbulent separated flows have presented fundamental challenges in validation between experimental and numerical approaches. As recognized by the CFD Vision 2030 study commissioned by NASA, validation of RANS models and scale-resolving methods for turbulent flows requires the support of advanced, high-fidelity experiments designated specifically for CFD implementation. In accordance with this effort, a new test platform, referred to as the NASA Axisymmetric Afterbody, was designed to obtain detailed information in a flow with a smooth, adverse-pressure gradient induced separation. The parametric body offers a range of flow behaviors from fully attached, incipient separation, to fully separated flow at subsonic conditions. In an initial effort to validate CFD capabilities, surface pressure measurements and flow visualizations at Re=180,000 are compared against several RANS turbulence models to understand the separation behaviors and identify critical variability between the models. Results indicate potential discrepancies due to the effect of Reynolds number and physical tunnel blockage. Ongoing work will continue the experimental campaign to obtain off-body flow measurements using SPIV and LDV techniques to yield further insight. [Preview Abstract] |
Monday, November 25, 2019 3:03PM - 3:16PM |
L15.00007: The law of incipient separation for turbulent flows as inferred by RANS Dawei Lu, Abhiram Aithal, Antonino Ferrante We have performed Reynolds-averaged Navier-Stokes (RANS) computations of incompressible turbulent boundary layer with adverse pressure gradient over two-dimensional smooth curved ramps of length $L$ for $982\leq Re_\theta \leq 3698$. First, we have validated the RANS by comparing the results with the experiments of Song \& Eaton ({\em Expts. Fluids}, 2004) for the separated flow over an arc at $Re_\theta=1100$. Then, we have investigated the effects of the ramp slope and curvature on the skin-friction and pressure coefficients. Our results show a numerical criterion of incipient flow separation determined only by the geometrical parameters of maximum slope, $|z'|_{\text{max}}$, length, $L$, and height, $h$, of the ramp, and by $Re_L$. Specifically, incipient separation occurs when $|z'|_{\text{max}}$ normalized by $\tilde{h}=h/L$ ($|\hat{z}'|_{\text{max}}=|z'|_{\text{max}}/\tilde{h}$) reaches a critical value that is determined according to the following law: $|\hat{z}'|_{\text{crit}}=\alpha \tilde{h} Re_L^{-1/10}+ \beta$, where $\alpha<0$ and $\beta>0$ are constants. Accordingly, the flow separates over a curved smooth ramp for which $|\hat{z}'|_{\text{max}}>|\hat{z}'|_{\text{crit}}$. The uncertainty of the law is also reported. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700