Estimation of Uncertainties for a Model Validation Experiment in a Wind Tunnel

Abstract

A high-quality model validation experiment was performed in the NASA Langley Research Center Unitary Plan Wind Tunnel to assess the predictive accuracy of computational-fluid-dynamics models for a blunt-body supersonic retropropulsion configuration at freestream Mach numbers from 2.4 to 4.6. Static and fluctuating surface pressure data were acquired on a 5-in.-diam (127-mm-diam) test article with a forebody composed of a spherically blunted, 70 deg half-angle cone and a cylindrical aft body. One unpowered configuration with a smooth outer mold line was tested as well as three powered, forward-firing nozzle configurations: a centerline nozzle, three nozzles equally spaced around the forebody, and a combination with all four nozzles. A key objective of the experiment was the determination of experimental uncertainties from a range of sources such as random measurement variation, flowfield nonuniformity, and model/instrumentation uncertainties. This paper discusses 1) the design of the experiment to best capture these uncertainties for the baseline unpowered configuration, 2) the methodology used in quantifying the various sources of uncertainty, and 3) examples of the uncertainties applied to unpowered and powered experimental results. The uncertainty analysis, which concentrates on the unpowered configuration, showed that flowfield nonuniformity was the dominant contributor to the overall uncertainty. This finding is in agreement with other wind-tunnel experiments that have quantified various sources of uncertainty.