The influence of small distributed surface roughness on disturbance amplification in a Mach 4.5 Blasius boundary-layer was investigated by numerical simulation of Navier-Stokes (N-S) equations. Distributed roughness was simulated by applying the wall boundary condition onto the smooth wall through a method of Taylor expansion. Different parameters of roughness and disturbance were considered including height

spacing

length of roughness and frequency of disturbances. Results show that distributed roughness affects the disturbance amplification by altering the basic flow. Distributed roughness shifts the unstable area to lower frequency for upstream flow field and to higher frequency for downstream flow field. Generally

for lower frequency disturbances near the lower branch of the neutral stability curve in the vicinity of roughness

the amplification was damped

while for higher frequency disturbances near the upper branch of the neutral stability curve

the amplification was amplified.