Control of oblique-type breakdown in a supersonic boundary layer employing streaks

Abstract

The effectiveness of streak modes in controlling the oblique-type breakdown in a supersonic boundary-layer at Mach 2.0 is investigated using direct numerical simulations. Investigations in the literature have shown the effectiveness of streak modes in delaying the onset of transition dominated by two-dimensional waves, but in oblique breakdown, three-dimensional waves and a strong streak mode dominate the transition process. Paredes et al. (J. Fluid Mech., vol. 831, 2017, pp. 524–553) discussed the possible stabilization of supersonic boundary layers by optimally growing streaks using parabolized stability equations. However, no study has as yet been reported regarding direct nonlinear control of oblique breakdown. This study deals with the effects of large-amplitude decaying streak modes generated by a blowing–suction strip at the wall to control full breakdown in a reference case. Modes with four to five times the fundamental wavenumber are found to be beneficial for controlling the transition. In the first region after the control-mode forcing, the beneficial mean-flow distortion (MFD), generated by inducing the control mode, is solely responsible for hampering the growth of the fundamental-mode. On the whole, the MFD and the three-dimensional part of the control contribute equally towards controlling the oblique breakdown. The results show significant suppression of transition, and substantial improvements have been observed in the levels of the skin-friction coefficient and wall-temperature in comparison to the uncontrolled case. Moreover, refreshing the control using an additional downstream control strip increases the gain. However, the forcing amplitude must be carefully chosen in order not to introduce a generalized inflection point in the spanwise averaged mean flow invoking enhanced disturbance growth.

Mechanism for frustum transition over blunt cones at hypersonic speeds

“…At the further downstream locations, the disturbance amplitude begins to increase close to the wall, leading to the higher slope of the skin friction curve as observed in figure 8(a). Recent studies have shown that under certain set of parameters, stationary streaks can stabilize oblique first-mode waves in supersonic boundary-layer flows (Paredes et al 2017;Sharma et al 2019) and Mack-mode waves in hypersonic boundary-layer flows (Paredes, Choudhari & Li 2019a). However, at large enough amplitudes, the same streaks are able to induce transition via streak instabilities (Paredes et al 2017(Paredes et al , 2019a.…”

Control of laminar breakdown in a supersonic boundary layer employing streaks

“…Building on the previous results the present DNS study is aimed at providing clear evidence of the robustness of the control technique employing steady streaks at a supersonic Mach number. The paper is organized as follows: first, we give details about the computational set-up used and its validation by comparing with results by Fezer & Kloker (2000) and Sharma et al (2019), where different DNS codes have been used. Following this, the control streaks are applied to a boundary layer perturbed by fundamental and subharmonic disturbances, simultaneously.…”

Optimization of a Fluidic Vortex Generator’s Control in a Transonic Channel Flow

“…Fluidic control has proven to be a very versatile control mean that, for example, has been successfully employed to manage the transition process in compressible flows (see Refs. [11,12]). These methods require a close consideration of the complete problem.…”