Active control of compressible channel flow up to Mab=3 using direct numerical simulations with spanwise velocity modulation at the walls

Abstract

Active turbulence control has been pursued continuously for the last decades, striving for an altered, energetically more favorable flow. In this article, our focus is on a promising method inducing a spanwise wall movement in order to reduce turbulence intensity and hence friction drag, investigated by means of direct numerical simulation. This approach transforms a previously time dependent oscillatory wall motion into a static spatial modulation with prescribed wavelength in the streamwise direction [48]. Most procedures related to turbulence control including the present one have been overwhelmingly applied to incompressible flow. This work is different and novel to the effect, that this control method is applied to compressible, supersonic channel flow up to a bulk Mach number of Ma=3. Due to substantial variations of viscosity, density, and temperature within the near‐wall region in supersonic flow, the impact of the control method is altered compared to solenoidal flow conditions. By creating a data set of different Mach‐/Reynolds numbers and control parameters, knowledge is gained in which way the effectiveness of oscillatory techniques and physical mechanisms change under the influence of compressibility. It is shown that the control method is able to effectively reduce turbulence levels and lead to large drag reduction levels in compressible supersonic flow. Variable property effects even enhance this behavior for the whole set of investigated parameters. Overall, the higher Mach number cases show a larger net power saving compared to the incompressible ones. Furthermore, we observe an increase of the optimum wavelength with increasing Mach number, which helps in guiding optimal implementations of such a control method.

Turbulent drag reduction with streamwise-travelling waves in the compressible regime

“…(1995) for the plane channel, and employed in all previous compressible studies of drag reduction by spanwise wall motion (Fang et al. 2009; Yao & Hussain 2019; Ruby & Foysi 2022). The ZBC simulations indicate that compressibility leads to a larger drag reduction achieved by spanwise forcing.…”

“…The few available compressible data are from Yao & Hussain (2019), who considered the oscillating wall only, at the slightly higher for and for . Moreover, the data points computed by Ruby & Foysi (2022) for a stationary wave are at and .…”

Preface to special issue on direct numerical simulations of turbulent flows—Part I

“…Ruby and Foysi [8] use DNS of compressible channel flows up to bulk Mach number Ma b = 3 to explore spanwise wall velocity modulation as a mechanism to actively control turbulence. Because of the strong fluctuations in viscosity, density and temperature within the near-wall region of the supersonic flow, the effect of the control method is substantially modified as compared to incompressible flow conditions [10].…”

Spatial discretization effects in spanwise forcing for turbulent drag reduction

“…The StTW, introduced by Quadrio, Ricco & Viotti (2009), are interesting owing mainly to their good energetic performance, which is preserved at high Reynolds numbers (Gatti & Quadrio 2016). The StTW are effective even in compressible and supersonic flows (Ruby & Foysi 2022;Gattere et al 2024), and have been demonstrated to affect favourably the aerodynamic drag of a three-dimensional body (Banchetti, Luchini & Quadrio 2020), up to the point that an actuation over a limited portion of the wing of an airplane in transonic flight reduces the total drag of the aircraft by nearly 10 % at a negligible energy cost (Quadrio et al 2022).…”