Finite roughness effect on modal growth of a hypersonic boundary layer

Abstract

Numerical simulation of roughness effect on modal growth is conducted on a hypersonic flat-plate at Mach 5.92. The steady base flow is firstly simulated by solving compressible Navier-Stokes equations. Stability characteristics of boundary-layer waves are analyzed by linear stability theory (LST). In stability simulations, two-dimensional disturbances corresponding to mode S or mode F at a frequency of 100 kHz are introduced near the leading edge of the flat-plate. Roughness with adjustable height is placed into four locations with respect to the disturbance synchronization point. It is found that upstream of synchronization point, disturbance is amplified by roughness with a stronger strength for taller roughness. On the other hand, disturbance is damped when the roughness is placed at or downstream of synchronization point. Different from upstream cases, tall roughness damps disturbance instead of amplifying it. We believe the relative location of synchronization point and roughness is a candidate to explain roughness delay transition as previous experiments have shown. Our results also show that roughness effect on mode S and mode F are very alike. In addition, a disturbance with a wide bandwidth is planned and will be imposed in the future.

Second Mode Suppression in Hypersonic Boundary Layer by Roughness: Design and Experiments

“…Zhong's group argues that 2-D roughness elements can damp 2-D disturbances if the roughness element, with a height less than the local boundary-layer thickness, is downstream of the synchronization point [14]. This finding has motivated a series of parametric studies on roughness effects including roughness locations, heights, and widths by Fong et al [17][18][19]. All results are consistent with the initial finding that 2-D roughness elements can damp 2-D disturbances and have shown the importance of roughness locations and synchronization locations.…”

Receptivity of the Boundary Layer over a Blunt Wedge with Distributed Roughness at Mach 6

“…Fast Fourier spectrum analysis (FFSA) is used to decompose the time domain signal in the boundary layer and expand it in the frequency domain to get the evolution process of the acoustic disturbance with different frequencies. This method is widely used to analyze receptivity of the hypersonic boundary layer with roughness under freestream disturbances, and satisfactory results are attained [21,39]. The Fourier transform formula is as follows:…”

Integrated Theoretical, Computational, and Experimental Studies for Transition Estimation and Control

“…Examined laminar flow control using 2-D roughness [6,10,66,67,68] Examined the receptivity of freestream disturbances to hypersonic boundary layers [24, 41, 43, 44, 84, 85, 86, 100-104, 159, 160, 171, 176, 180, 181].…”