Pre-Flight Ground Testing of the Full-Scale FRESH FX- 1 at Fully Duplicated Flight Conditions

As part of an experimental study to obtain detailed heating and pressure data over the full-scale FRESH FX-1 flight geometry, CUBRC has completed a 30-run matrix of ground tests, sponsored by the AFOSR, to determine the optimal flight hardware and instrumentation configuration necessary to achieve and make measurements of desired flow phenomena during the flight experiment. FRESH FX-1 stands for Fundamental RESearch in Hypersonics Flight eXperiments and the flight vehicle consists of a blunt nose, cone, cylinder, and flare regions. The primary objective of the FRESH FX-1 flight experiment is to collect high quality flight data to be used for CFD code and ground test facility validation in regions of boundary layer transition as well as regions of separated shock wave/boundary layer interaction at the cylinder/flare junction. While flight data will be acquired over the entire flight, data was obtained in LENS I over a range of Mach numbers from 6.5 to 7.4, and Reynolds numbers of 2E+06 to 5.5E+6 duplicating the reentry trajectory points that gave the best chance to measure the transition process on the cone and have a turbulent separated flow that reattached onto the flare section. These test condition ranges were determined directly from the nominal descent trajectory of the Australian Terrier-Orion launch vehicle that would serve as the booster for FRESH FX-1. The program was completed in two distinct phases. The first phase consisted of a geometry study to aid in the selection of the proper nose radius to achieve the desired transition location on the cone, and to establish the flare angle necessary to achieve a turbulent separation zone with reattachment back onto the flare. These experimental results were used directly in determining the proper nose radius to employ for both the second phase of the ground test and for use on the actual flight vehicle and to determine where additional instrumentation should be placed to obtain higher resolution spatially in the transition region. These areas included the transitional region on the cone as the flow goes from fully laminar to fully turbulent, and at the cylinder/flare junction to obtain detailed information in the shock wave/turbulent boundary layer region with separation and reattachment. Additionally high speed schlieren movies were taken during the first phase to assess the separation behavior in the cylinder/flare region. It was very desirable to achieve turbulent separation with reattachment on the flare far enough upstream to leave an attached length on the flare after reattachment to serve as a bounding condition for CFD validation. Secondary objectives of the first phase included testing the model at angle of attack and heating the model nose to flight-like temperatures to assess the influence of these factors on the transition front and separation/reattachment process. In addition to the experimental data, CUBRC also performed a large amount of CFD analysis to confirm and validate not only the tunnel flow conditions, but also 2D and 3D flows over the model itself. Laminar and turbulent solutions have been obtained using the DPLR code, including several distinct turbulence models. This analysis is a standard part of any experimental program at CUBRC, and this information was of key importance for post-test data quality analysis (correlation) and understanding particular phenomena seen in the data. A key part of the computational study involved establishing "n-factors" to compare DPLR and STABL transition results to those obtained in the experiment. These comparisons were ultimately employed to extrapolate the transition location to flight. All work during this effort was sponsored by AFOSR