The effect of streamwise-traveling waves on the drag variation of compressible channel flow

The influence of streamwise-traveling waves imposed at the walls on drag variation in compressible channel flow is investigated using direct numerical simulations. The variations in drag are mapped in the frequency-wavenumber (ω ⁺,k⁺) ( ω + , k + ) space for three bulk Mach numbers, Mab=0.3, 0.8 M a b = 0.3 , 0.8 and 1.5, at a fixed bulk Reynolds number Reb=3000 R e b = 3000 . The traveling waves significantly modify friction drag, showing similar trends across all Mab M a b . Depending on the phase speed ( c⁺ c + ), the waves can induce either drag reduction ( $$DR$$ DR ) or drag increase ( $$DI$$ DI ). In the region of low c⁺ c + , the $$DR$$ DR is mostly around 40% 40 % , especially when Mab=1.5 M a b = 1.5 , where it reaches 66.6% 66.6 % . At moderate c⁺ c + , a substantial $$DI$$ DI occurs. At high <jat