The measurement error analysis when a pitot probe is used in supersonic air flow

Abstract

Pitot probes enable a simple and convenient way of measuring mean velocity in air flow. The contrastive numerical simulation between free supersonic airflow and pitot tube at different positions in supersonic air flow was performed using Navier-Stokes equations, the ENN scheme with time-dependent boundary conditions (TDBC) and the Spalart-Allmaras turbulence model. The physical experimental results including pitot pressure and shadowgraph are also presented. Numerical results coincide with the experimental data. The flow characteristics of the pitot probe on the supersonic flow structure show that the measurement gives actually the total pressure behind the detached shock wave by using the pitot probe to measure the total pressure. The measurement result of the distribution of the total pressure can still represent the real free jet flow. The similar features of the intersection and reflection of shock waves can be identified. The difference between the measurement results and the actual ones is smaller than 10%. When the pitot probe is used to measure the region of L=0–4D, the measurement is smaller than the real one due to the increase of the shock wave strength. The difference becomes larger where the waves intersect. If the pitot probe is put at L=8D–10D, where the flow changes from supersonic to subsonic, the addition of the pitot probe turns the original supersonic flow region subsonic and causes bigger measurement errors.