LES of Channel Turbulence with an unsteady pressure gradient.

All the runs have the same geometry (x streamwise, y spanwis, z vertical) and viscosity. The pressure gradient in each run is given by C+a/Tcos(t/T), C and a are kept constant, and T is varied. Table lists the relevant parameters of each simulation.

The following plots show phase averaged streamwise velocity, dU/dz, the turbulent kinetic energy and the turbulent k.e. production term -dU/dz<uw>.
Re100 , Re150 , Re200 , Re300 , Re500 , Re1000 .

Now we project the time series of spatially averaged (over x and y) quantities f(z,t) onto C(z)+A(z) cos(t/T+phase(z)), that is we find C, A and phase that minimize (f(t)-C(z)-A(z) cos(t/T+phase(z)))^2. In the following plots, C(z) is in blue and A(z) in green. mean streamwise velocity, mean streamwise turbulent kinetic energy, mean <uw> Reynolds stress, and the Smagorinsky coefficient C_s .

Spectra

Phase averaged streamwise spectra of U at 8 different times during one cycle at z+=8,13,31,110 (top to bottom) and t=0,T/8,T/4,3T/8,...,7T/8 (left to right). Plots are offset in wavelength for clarity.

Re_\delta	U, Kx	U, Ky	V, Kx	V, Ky	W, Kx	W, Ky
100	X	X	X	X	X	X
150	X	X	X	X	X	X
200	X	X	X	X	X	X
300	X	X	X	X	X	X

1000	X	X	X	X	X	X

Links: Slides given at the 1999 APS DFD meeting (postscript)