Test Program for a Dual-mode Scramjet

Since flow at hypersonic Mach numbers (M≥5) behaves very differently from flow at subsonic or supersonic Mach numbers, the testing of hypersonic engines involves challenges not encountered in engine testing for flight in other regimes. For hypersonic Mach numbers, thermal, chemical, radiative, and ablative effects become important. Energy and heat transfer considerations make continuous-run, full scale testing at hypersonic Mach numbers difficult or impossible. While facilities have been devised specifically to study certain aspects of hypersonic flight, no single facility has the ability to simulate all the flow conditions that a hypersonic vehicle or engine may encounter.

Flight can be considered the ultimate test of a hypersonic vehicle or engine because no facility effects are present. It is often the case, however, that budgetary, thermal, structural, or other logistical limitations restrict the range of diagnostics available for flight vehicle testing. Flight programs also incur significant risk that is generally not present or is significantly reduced for ground testing programs. If an unguided rocket is used to minimize cost, the likelihood that the payload will achieve the desired test conditions decreases. If a reactive control system is utilized to increase the likelihood that the payload will achieve the desired test conditions, both complexity and cost increase significantly. As such, flight programs are nearly always augmented with significant ground testing to reduce risk and confirm engine operability limits. Often a range of wind tunnels is used in order to resolve the inherent deficiencies of any one type of ground test facility. Two common shortcomings of hypersonic test facilities are the short test time associated with shock-heated facilities and the contaminated or vitiated test gas associated with combustion-heated facilities.

This dissertation details a test program for a dual-mode scramjet which involves both ground and flight experiments in support of the Short Duration Propulsion Test and Evaluation (SDPTE) program, which aims to resolve the effects of a short test time and vitiated test medium on the operation and performance of a dual-mode scramjet (DMSJ). Included is background information related to previous scramjet test programs and their objectives, information on the design of the ground and flight tests for this program, as well as a novel rocket dispersion reduction scheme aimed at increasing the probability of a successful scramjet test flight.

As part of this work, a hypersonic inlet for flight and freejet ground testing was designed and tested in an impulse facility. In these same tests, dual-mode operation of a DMSJ was demonstrated. Since only one test flight is planned for the SDPTE program and a scramjet’s operation is directly influenced by the freestream conditions it encounters, a novel method was devised to reduce dispersion in test conditions seen by a scramjet flight-tested aboard a two-stage, unguided, spin-stabilized, sounding rocket. This involved altering the second stage ignition time to ensure that the vehicle passes through the test Mach number at the desired altitude. This method was tested through Monte Carlo simulation and was shown to increase the chances of a successful test flight from 71% to over 99%. The work presented in this dissertation advances the state of scramjet testing and serves as a framework for the design of a scramjet ground and flight test campaign.

Approved for public release; distribution is unlimited. AEDC PA 2012-083