Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session T36: Boundary Layer Pressure Gradient Effect I |
Hide Abstracts |
Chair: Thomas Ward, University of Virginia Room: 355 B |
Monday, November 25, 2024 4:45PM - 4:58PM |
T36.00001: Similarity Between Adverse Pressure Gradient Boundary Layers on Rough and Smooth Walls Ralph J Volino, Michael P Schultz Outside the roughness sublayer, outer layer similarity is observed between canonical zero pressure gradient (ZPG) boundary layers on rough and smooth walls. Profiles of mean velocity and turbulence statistics agree when normalized using the boundary layer thickness and the friction velocity. This similarity allows models developed for smooth wall conditions to be used for flows over rough surfaces, with the roughness effect entering only through the wall boundary condition. New results indicate that similarity holds for adverse pressure gradient (APG) conditions if the Clauser pressure gradient parameter, β=(δ*/τo)(dP/dx), is matched. If the rate of change of β is not too high, the boundary layer can reach a state of near equilibrium, and similarity is observed independent of upstream β history. If the rate of change of β is rapid and/or a departure from equilibrium is caused by the pressure gradient upstream of the APG region, similarity between the rough- and smooth-wall cases can still be achieved if the β history is matched. A dimensionless streamwise coordinate, (xuτo2)/(δoUeo2) (with δo, uτo, and Ueo the boundary layer thickness, friction velocity and freestream velocity at the start of the APG) is proposed for defining the β history. Experimental results from APG boundary layers with a variety of APG strengths and upstream conditions (e.g. a ZPG or a favorable pressure gradient immediately preceding the APG) will be presented and compared to show the extent of similarity in the mean velocity and Reynolds stresses between rough- and smooth-wall cases. |
Monday, November 25, 2024 4:58PM - 5:11PM |
T36.00002: Experimental investigation of the ability of yawed riblet geometries to generate near-wall spanwise flows for control applications Yu Xia, Hafiz N Aliffrananda, Ivan Marusic, Daniel Chung, Nicholas Hutchins Widely spaced yawed riblets, with large height-to-spacing ratios, are investigated for their promise to generate spanwise near-wall flows. Such induced flows could potentially be exploited for control or near-wall steering of turbulent boundary layers. These generated spanwise flows are small in magnitude (generally O(Uτ)) and diminish in strength rapidly with increasing wall-normal distance from the riblet crest. To meet this experimental challenge, we use a unique rotating hot-wire probe arrangement, which enables the local mean flow angle to be determined with high accuracy. DNS data from simulations on matched surfaces are used to optimise and validate this measurement approach. Having established this measurement technique, we are able to verify the increased efficacy of yawed widely spaced riblets to generate much stronger spanwise flows as compared to conventional yawed riblet geometries. The required development length over yawed surfaces to fully form these spanwise induced flows is also investigated. This is a crucial first step in understanding the minimum viable streamwise wavelengths that will permit meandering arrangements of these riblets to generate spatially oscillating spanwise near-wall flows for control purposes. |
Monday, November 25, 2024 5:11PM - 5:24PM |
T36.00003: Contributions of very low wavenumbers to wall pressure and wall shear stress in high Reynolds number zero pressure gradient turbulent boundary layers. Facundo Cabrera-Booman, Vijaya Rama Reddy Gudla, Liuyang Ding, Marcus Hultmark, Alexander J Smits, Ivan Marusic, Beverley J McKeon Wall-bounded flows are ubiquitous in industrial applications (e.g., over aircraft wings and submarines) and affect vehicle performance through the resulting fluctuations in wall shear stress (associated with skin-friction drag) and wall pressure (linked to flow-induced vibrations). Subconvective wavenumber contributions to wall pressure and shear stress serve as crucial inputs to noise and vibration models; the scaling of these contributions relies on extrapolation from low Reynolds number measurements. However, it is known that wall turbulence is altered at high Reynolds numbers by the emergence and increasing energetic content of "very large-scale motions". |
Monday, November 25, 2024 5:24PM - 5:37PM |
T36.00004: Reynolds number dependence of length scales governing turbulent flow separation in wall-modeled LES Rahul Agrawal, Sanjeeb T Bose, Parviz Moin In this work, we propose a Reynolds number (Re) scaling for the number of grid points (Ncv) required in wall-modeled LES (WMLES) of separated turbulent boundary layers (TBL). Based on the various time scales in a non-equilibrium TBL, a definition of the near-wall “under-equilibrium" scales is proposed (where “equilibrium" refers to a quasi-balance between the viscous and the pressure gradient terms). This length scale is shown to vary with Reynolds number as lp ∼ Re−2/3, which implies that for a flow solver with nested grids, the grid point requirements for capturing regions of flow separation in WMLES employing equilibrium wall closures scale as Ncv ∼ Re4/3. A-priori analysis demonstrates that the resolution (Δ) required to reasonably predict the wall stress in several non-equilibrium flows is at least O(10) lp, irrespective of the Reynolds number and Clauser parameter. Three flows are considered a-posteriori: the Boeing speed bump (Uzun & Malik, 2022), an arc shaped diffuser (Song & Eaton 2004), and a smooth ramp (Simmons et al., 2017); our results corroborate the a-priori estimates to demonstrate that the grid point requirements for capturing flow separation are more stringent than the estimates (Ncv ∼ Re1) of Choi and Moin. Finally, we also show that an appropriate non-equilibrium wall model can reduce this cost scaling to Ncv ∼ Re1 even in separated flow regions. |
Monday, November 25, 2024 5:37PM - 5:50PM |
T36.00005: The Effects of Pressure Gradients and Surface Roughness on Turbulent Boundary Layers Madeline S Fischer, Ondrej Fercak, Sara Thoi, Dennice F Gayme, Charles Meneveau, Raúl Bayoán Cal The effects of pressure gradients applied to a flat surface with heterogeneous roughness for turbulent boundary layers is not well understood. The current study experimentally investigates this fundamental interaction by characterizing the development of a turbulent boundary layer over a flat plate with strips with different roughnesses, each 0.10 m wide by 3.7 m long, subjected to both favorable and adverse pressure gradients. The study is performed in the Portland State University wind tunnel with a test section of 5 m in length, 1.2 m in width, and 0.8 m in height. The adverse and favorable pressure gradients are applied to the plate by adjusting the angles of the ceiling panels of the wind tunnel such that flow separation does not occur at any point along the plate, which would occur if the plate itself were tilted. Boundary layer development for each case is characterized based on particle image velocimetry data. |
Monday, November 25, 2024 5:50PM - 6:03PM |
T36.00006: Towards Wall modeled Large Eddy Simulation of a Turning Body of Revolution Mitchell Fowler, Benjamin A Minnick Accurate simulation of flow over bodies of revolution (BOR) is necessary for force and moment predictions of maneuvering vehicles in naval applications. Large eddy simulation (LES) can provide the means for the level of fidelity needed; however, LES for a BOR still remains challenging for practical engineering applications due to the vast range of scales and large domain size needed to capture all the relevant flow features. In this work, we present an approach to simulate flow over a BOR under steady turning conditions. To reduce the domain size, analytical potential flow solutions are used for the far-field boundary condition. To reduce the near-wall resolution requirement, a wall model is used as a wall stress boundary condition. To keep to the benefits of a simple Cartesian grid, the BOR is mapped to a flat plate where computations are performed. This approach permits LES of these challenging flows to inform maneuvering predictions. First, the modeling framework needed is discussed along with the associated cost savings. Then, the numerical aspects of the code are outlined. Finally, preliminary details for performing wall modeled LES of a BOR undergoing steady turning conditions are discussed. |
Monday, November 25, 2024 6:03PM - 6:16PM |
T36.00007: DNS and Reynolds Stress Transport Modeling of Adverse Pressure Gradient Flat Plate Flow Abdullah Geduk, Vishal A Wadhai, Shyam S Nair, Xiang Yang, Robert F Kunz A systematic study is carried out to study the Reynolds stress budgets in strongly adverse pressure gradient turbulent boundary layers. We perform Direct Numerical Simulations (DNS) of Reτ = 500 boundary layers with Clauser pressure-gradient parameters of 0, 10 and 20. The focus of these simulations and their statistics is to obtain term-wise comparisons of the budget terms in the Reynolds stress transport equations for use in Reynolds Averaged Navier-Stokes (RANS) model assessments. Accordingly, we present the exact closure terms for material transport, production, turbulent and pressure diffusion, redistribution and dissipation. These are compared against DNS predictions for the sub-models (diffusion, redistribution, dissipation) that have been proposed for various sublayer resolved conventional Full Reynolds Stress Models (FRSM). Additionally, we study the results returned by the RANS FRSM code itself for these mean statistics. Several severe shortcomings are observed in the submodel forms which conspire to compromise the FRSM accuracy in predicting even low order moments. |
Monday, November 25, 2024 6:16PM - 6:29PM |
T36.00008: A low-fidelity approach to design tailored flow conditions for non-zero pressure gradient turbulent boundary layers. Md Raihan Ali Khan, Johan Larsson Non-zero pressure gradient turbulent boundary layers (TBLs) hold significant importance in almost all kinds of engineering applications. To systematically study these TBLs, a low-fidelity tool has been developed to design boundary conditions to create desired specific flow conditions. This tool facilitates the creation of both equilibrium and non-equilibrium non-zero pressure gradient TBL scenarios. The scope and performance of this tool have been tested against high-fidelity data, demonstrating its effectiveness in generating the desired flow conditions for further study. |
Monday, November 25, 2024 6:29PM - 6:42PM |
T36.00009: Resolvent analysis of a turbulent self-similar adverse pressure gradient turbulent boundary layer at the verge of separation Julio Soria, Antonio Matas, Kevin Liu, Salvador Rey Gomez, Tomek M Jaroslawski, Beverley J McKeon There has been much theoretical, experimental and numerical research into turbulent boundary layers (TBLs) with the vast majority focused on the zero-pressure-gradient case. Concerning its adverse pressure gradient (APG) counterpart, however, many aspects of their scaling, structure and stability remain unresolved. The study of a canonical APG-TBL is, therefore, of the utmost importance. The self-similar (SS-APG-TBL) is arguably the most appropriate canonical form to study as a canonical APG-TBL. This SS-APG-TBL exists at the verge of separation, where the mean wall-shear stress is zero and the non-dimensional pressure parameter β → ∞. A DNS of a SS-ABG-TBL with a momentum thickness-based Reynolds number range from 570 to 13,800, and a self-similar region with momentum thickness-based Reynolds number range of 10,000 to 12,300 has been undertaken. This DNS has been used as the basis for a bi-global resolvent analysis to provide insight into the linear amplification from linearised Navier-Stokes equations that uses only the mean flow field of this flow. A bi-global resolvent analysis sweep over a range of temporal frequencies and spanwise waveumbers has been undertaken. The results reveal that the maximum gain and its resolvent velocity response mode are closely associated with structures that correspond to intense u'v' structures, as well as to the location of maximum turbulence intensity that is located at one displacement thickness from the wall with a spanwise length scale of approximately 1.5 displacement thicknesses. |
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. |
© 2025 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