MAE Seminar: Flow control strategies for turbulent jets and curved internal flows

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MAE Seminar: Flow control strategies for turbulent jets and curved internal flows
Date: February 12, 2026
Time: 12:50 PM Location: MAE-A 303

Dr. Akhil Nekkanti
Postdoctoral Scholar
Center for Turbulence Research
Stanford University

Abstract
Controlling turbulence in fluid flows offers transformative benefits in aerospace, wind energy, and transportation, such as reducing drag, mitigating noise, and improving pressure recovery. In this talk, I will present two problems: (i) flow control to enhance mixing in turbulent jets and (ii) opposition control to improve pressure recovery in curved internal flows.
First, we investigate nonlinear interactions during vortex pairing in transitional jets. The shear layer rolls up into fundamental vortices that merge into subharmonic structures and then into a second subharmonic. The energy transfer during this process is evaluated using the spectral turbulent kinetic energy equation, focusing on dominant coherent structures identified through spectral proper orthogonal decomposition. Our findings reveal an inverse energy cascade from the fundamental wave to its subharmonic. Next, we introduce bispectral mode decomposition, a technique that optimizes triple correlations in frequency space to identify dominant triadic interactions in fully turbulent jets. We find strong triadic coupling between Kelvin-Helmholtz wavepackets, their conjugates, and streamwise streaks. Building on this, we perform open-loop control by actuating the wavenumbers and frequencies of the KH wavepackets, producing significant mean-flow distortion through amplified streaks.
Second, we focus on flow control in serpentine diffusers. Blended-wing-body configurations are emerging as a promising design for future military aircraft, but they require complex inlet systems whose high-curvature bends generate vortices, shock waves, and flow separation, leading to pressure losses, flow distortion, and reduced stall margin. We perform wall-modeled large-eddy simulations to identify the mechanisms driving flow distortion. We perform wall-modeled large-eddy simulations to identify the mechanisms driving flow distortion. We then apply opposition control to suppress the root cause, Görtler vortices, significantly improving pressure recovery.

Biography
Akhil Nekkanti is a postdoctoral scholar at the Center for Turbulence Research at Stanford. Previously, he was a postdoctoral scholar at Caltech, working with Tim Colonius. He received his Ph.D. from UC San Diego under the guidance of Prof. Oliver Schmidt and his bachelor’s degree from the Indian Institute of Technology, Ropar. His primary interests are turbulent flows with a particular focus on high-fidelity simulations, reduced-order modeling, and hydrodynamic stability. He received the ‘Outstanding Graduate Student in MAE, 2023’ award at UCSD for best thesis, and his paper was selected as one of the best papers at the 12th International Symposium on Turbulent Shear Flow Phenomena.

Faculty Host: Dr. Richard Lind, Jr.