Uncertainty Quantification of Flow Uniformity Measurements in a Slotted Wall Wind Tunnel

The need for a more complete understanding of the flow behavior in aerodynamic wind tunnels has increased as they have become vital tools not only for vehicle development, but also for vehicle certification. One important aspect of the behavior is the empty test section flow, which in a conventional tunnel should be as uniform as possible. In order to assess the uniformity and ensure consistent behavior over time, accurate measurements need to be performed regularly. Furthermore, the uncertainties and errors of the measurements need to be minimized in order to resolve small non-uniformities. In this work, the quantification of the measurement uncertainties from the full measurement chain of the new flow uniformity measurement rig for the Volvo Cars aerodynamic wind tunnel is presented. The simulation based method used to account for flow interference of the probe mount is also discussed. The flow measurement rig is custom made to facilitate fast and accurate measurements with low interference. The cost is minimized by using standard off-the-shelf five hole probes and facility installed pressure measurement instrumentation, which are shown to give sufficient measurement quality when calibrated in situ. Example measurements of flow angularity and static pressure uniformity, with accompanying uncertainties, are presented and discussed.