Drag Reduction and Energy Saving by Spanwise Traveling Transversal Surface Waves for Flat Plate Flow

Marian Albers,Daniel Fernex,Pascal S Meysonnat,Wolfgang Schröder,Richard Semaan,Bernd R Noack

doi:10.1007/s10494-020-00110-8

Abstract

Wall-resolved large-eddy simulations are performed to study the impact of spanwise traveling transversal surface waves in zero-pressure gradient turbulent boundary layer flow.Eighty variations of wavelength, period, and amplitude of the space- and time-dependent sinusoidal wall motion are considered for a boundary layer at a momentum thickness based Reynolds number of {rm Re}_theta = 1000. The results show a strong decrease of friction drag of up to 26% and considerable net power saving of up to 10%. However, the highest net power saving does not occur at the maximum drag reduction. The drag reduction is modeled as a function of the actuation parameters by support vector regression using the LES data.A dependence of the spanwise pressure drag on the wavelength is found. A substantial attenuation of the near-wall turbulence intensity and especially a weakening of the near-wall velocity streaks are observed. Similarities between the current actuation technique and the method of a spanwise oscillating wall without any normal surface deflection are reported. In particular, the generation of a directional spanwise oscillating Stokes layer is found to be related to skin-friction reduction.

Highlights

Viscous drag in turbulent wall-bounded flows is one of the major contributors to the overall drag of flow over slender bodies in general and passenger planes in cruise flight in particular
We investigate the higher reduction trends with longer wavelengths and examine the flow sensitivities over the space spanned by the three actuation parameters, i.e., wavelength, wave period, and wave amplitude, using high-resolution large-eddy simulations (LES) of turbulent boundary layer flow
The parameter space defined by the wave amplitude, wave period, and wavelength was investigated based on 80 wave parameter setups for purely spanwise traveling waves

Summary

Introduction

Viscous drag in turbulent wall-bounded flows is one of the major contributors to the overall drag of flow over slender bodies in general and passenger planes in cruise flight in particular. Lowering turbulent friction drag is essential to meet future CO2 reduction goals. Besides preventing fully turbulent flow and benefiting from the considerably lower laminar drag (Spalart and McLean 2011), there is substantial past and ongoing research in the field of turbulent drag reduction. Can be adjusted to a range of flow conditions such that at least certain approaches can achieve higher net power saving. These results, hold mostly in canonical flow setups like turbulent channel flows under laboratory conditions, i.e., at extremely low technology readiness levels. The investigation and identification of the mechanisms of active drag reduction techniques might benefit from the development of improved or new passive approaches, e.g., passive wavy wall undulations (Ghebali et al 2017) inspired by the active technique of streamwise oscillations of spanwise wall velocity (Viotti et al 2009)

Methods

Results

Conclusion