Modeling, Simulations, and Analysis of Turbulent Boundary Layers Exhibiting Smooth Body Separation

Speaker: Rahul Agrawal, Ph.D. Candidate, Stanford University
March 6, 2025

Presentation

Please Note: Due to technical issues, audio in the seminar video recording begins at time 01:30.

Abstract

Wall bounded turbulence is ubiquitous in aerospace, and energy applications. Specifically in aerospace applications, often the flow detaches from the surface due to external forces such as pressure-gradients and shocks, which has a deteriorating effect on the aircraft performance. In this talk, we utilize the large-eddy simulation (LES) paradigm to study the phenomenon of incipient, smooth body flow separation over complex geometries.

Generally, in LES, conventional subgrid closure models assume an alignment between subgrid-stresses and resolved strain rates. However, this assumption has been shown to be over-restrictive, even in canonical flows.

Further, in several complex engineering flows, the high Reynolds numbers imply that the near-wall flow structure is left unresolved and instead, approximate boundary conditions (a “wall model”) are invoked to supply the wall stress. A commonly invoked wall closure is the equilibrium wall model which assumes that the near-wall flow follows the equilibrium law of the wall in the mean. However, in many realistic flows which experience prolonged action of pressure gradients, and eventually detach from the surface, the usage of an equilibrium closure has been shown to mispredict the wall-stress at affordable resolutions.

To this end, in this seminar, we discuss our new subgrid-closure and near-wall models for non-equilibrium flows that exhibit incipient separation. These models are validated in several canonical flows and applied in two complex flows: over a high-lift aircraft and inside a serpentine inlet diffuser. It is shown that the proposed models produce more accurate solutions (to within industry tolerances) than the conventional closure models at affordable grid resolutions.

Biography

Rahul Agrawal is a Ph.D. candidate at the Center for Turbulence Research at Stanford University under the advisement of Prof. Parviz Moin. He earned a bachelor’s in technology degree from the Indian Institute of Technology, Bombay, in Mechanical Engineering in 2020 and a master’s in Mechanical Engineering from Stanford in 2022. His PhD is supported by NASA, Boeing Research and Technology, and the Stanford School of Engineering Fellowships.

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