Development of functional relationships for air-data estimation using numerical simulations

Flush Air-Data Sensing (FADS) systems use an array of surface pressure measurements to infer the speed, position, and orientation of a vehicle in flight. The non-intrusive nature of such systems make them especially useful for hypersonic vehicles. Determining the functional relationship between measured surface pressure and the airdata of interest (e.g. Mach number, angle-of-attack, etc.) is the first step in implementing a FADS system. In this work, these functional relationships are developed by fitting surfaces/curves to a set of numerical simulations. In the absence of ground or flight test data, the resulting FADS algorithm is tested with a second set of numerical simulations. The largest error in predicted Mach number is ±0.2, in angle-of-attack is ±0.05°, in angle-of-sideslip is ±0.15°, and in freestream pressures is ±20 Pa

The hifire 7 flight experiment

The HIFiRE program is an Australian/US collaboration tasked with studying fundamental hypersonic phenomena and developing the technologies to enable future hypersonic flight. HIFiRE 7 is a free-flying scramjet experiment, the primary objective of which is to measure the thrust produced by a three-dimensional scramjet and compare the measurement to ground test data. It was launched from the Andøya Space Center in March, 2015; a component failure resulted in loss of data before the scramjet combustion experiment commenced. However, the flight experiment was successful in many aspects, including the achievement of several key technical objectives that will enable future hypersonic flight testing in Australia, and the demonstration of scramjet inlet self-starting at high altitude. This paper will describe the HIFiRE 7 experiment and present available flight data

Effects of oxygen enrichment on scramjet performance

This investigation quantifies the beneficial effects of oxygen enrichment on the combustion efficiency and specific thrust of a simplified planar scramjet engine fueled with gaseous hydrogen. Numerical modeling was used to examine the influence of fuel equivalence ratio and enrichment percentage. Broad agreement with experimental data is reported, but the present simulations provide considerably more detail, revealing aspects of the flow physics that could not be discerned from experimental data. Multiple Reynolds-averaged Navier–Stokes simulations were performed at Mach 12 equivalent freestream conditions with fuel equivalence ratios of 0.8–1.4 and enrichment percentages up to 20%. Trends in combustion efficiency with enrichment percentage are formulated for use in trajectory studies. The combustion efficiency and specific thrust are found to be significantly increased by enriching fuel with oxygen. The increases are greater than those expected from the additional propellant and complete consumption of premixed oxygen. We found that this is due to oxygen enrichment modifying the mixing layer properties within the scramjet such that the production of turbulence and therefore fuel/air mixing is increased. It is also shown that an optimal combustor length exists beyond which internal losses outweigh contributions from combustion

Shock tunnel experiments on oxygen enrichment in a hydrogen fuelled scramjet

Extension of scramjet operation into the hypervelocity regime (u > 3 km/s, M > 10) is critical for their use in access-to-space systems. As flight speeds increase, the net thrust of a scramjet engine is limited by increased fuel/air mixing length requirements, as well as the decreased ratio of energy available from stoichiometric fuel/air combustion relative to the specific kinetic energy of the captured air. One possible method for addressing these issues, known as oxygen enrichment, involves the premixing of oxygen with fuel before injection. This method provides a head start for mixing and also allows the possibility of fuel combustion at greater than stoichiometric proportions. This paper describes some exploratory shock tunnel experiments involving oxygen enrichment of gaseous hydrogen fuel in a scramjet at hypervelocity conditions. These experiments were conducted in a simple rectangular duct with a central strut injector and varying levels of enrichment. The measured pressure distributions show a positive effect of enrichment and indicate how this technique could be best used to extend the performance of hypervelocity scramjets to higher flight Mach number