The acoustic radiation from the turbulent boundary layer on the nozzle wall of a Mach 6 Ludwieg Tube is simulated using Direct Numerical Simulations ( DNS ) , with the flow conditions falling within the operational range of the Mach 6 Hypersonic Ludwieg Tube , Braunschweig ( HLB ) . The mean and turbulence statistics of the nozzle - wall boundary layer show good agreement with those predicted by Pate 's correlation and Reynolds Averaged Navier - Stokes ( RANS ) computations . The rms pressure fluctuation P'(rms)/T(w ) plateaus in the freestream core of the nozzle . The intensity of the freestream noise within the nozzle is approximately 20 % higher than that radiated from a single at pate with a similar freestream Mach number , potentially because of the contributions to the acoustic radiation from multiple azimuthal segments of the nozzle wall .