Experiments were conducted to study the feasibility to use a laser Doppler anemometer for measurements in the shock region and in particular the behavior of the particles which experience the sudden change of velocity across an aerodynamic shock. Instantaneous velocities were measured by traversing the measurement volume through an oblique shock. Shocks were generated by the supersonic flow of Mach number, M1 = 1.97 past double wedge models.
The main flow and the normal components of the velocity change in a finite distance called as the shock region. It has been found that the variation is linear at first and the rate decreases as the flow proceeds further downstream in the shock region. The influence of the particle lag cannot be ignored. The turbulences in the main flow and the normal flow directions increased in the shock region depending upon the strength of the shock. These typical variations have been observed at different locations on the shock and with different settings of the sensitivity against particle size. Large increase in the turbulences was observed without limiting the amplitudes of the collected Doppler signals, probably due to the presence of bigger seed particles which may not faithfully follow the flow. Measurements with amplitude limit seem to be accurate and show smaller increase of the turbulence within the shock region. Hence amplitude limit is recommended to obtain accurate turbulence values in flows having large velocity gradients. The mean velocity changes were found to be in agreement with the calculations.