Supersonic Particle Probes: Measurement of Internal Wall Losses

In the present study, the operating characteristics of supersonic particle probes are investigated. In particular, characteristics such as internal wall deposition and pressure recovery are examined. Three basic probe designs were tested in a cold flow experiment designed to simulate the hot, hostile environment of rocket and jet engine plumes. The probe designs consisted of two internal shock probes (Dehne and Colket probes) and one external shock probe (McGregor probe). In the internal shock probes the compression from supersonic to subsonic flow occurred either in a constant area throat (Dehne) or at a sudden expansion (Colket). In the external shock or McGregor probe, the shock was positioned slightly outside the entrance of the probe.

From deposition studies performed on the probes, three factors were found to enhance deposition. These factors were: 1) shock-boundary layer interaction, 2) particle-boundary layer interaction, and 3) stagnation zones at sudden expansions. The probe with the lowest deposition was a McGregor probe with a 2.0° divergence angle. Using test particles with diameters of 1.0, 1.5, 2.0, and 2.5 μm, the average losses in the McGregor probe were 14% while in the Colket and Dehne probes the losses were 18% and 22%, respectively. Pressure recovery was also found to be the greatest in the McGregor probe with 48% of the initial stagnation pressure regained. The Colket probe had only a 7% pressure recovery.