ERI: Experimental Investigation of Compressibility Effects on Turbulent Kinetic Energy Production in Supersonic Flows

Missouri University Of Science And Technology, Rolla MO

Investigators

Abstract

Hypersonic flight offers the potential to revolutionize global travel and space exploration. A crucial technology for making this a reality is the development of efficient supersonic combustors for air-breathing hypersonic engines. These combustors differ from traditional ones in their extremely short residence times, typically around 1 millisecond. In such a short time, the fuel must be injected, vaporized (for liquid fuels), dispersed, and mixed to the molecular level with the incoming air before combustion can occur. Turbulence, which aids dispersion and mixing, is vital in this process. However, understanding how compressibility affects turbulence production is still incomplete, slowing down hypersonic flight development. This project aims to investigate compressibility effects on turbulence by directly measuring turbulence in the Mach 3 wind tunnel at Missouri University of Science and Technology. As turbulence plays a key role in the mixing process, understanding its production and how it is affected by compressibility would facilitate a better understanding of the mixing process in supersonic flows and the design of supersonic combustors. While turbulence production in supersonic flows has been recently investigated, compressibility effects – particularly on density fluctuations – have been largely neglected in non-wall-bounded flows such as jets and shear, which are relevant for mixing applications. Recent research indicates that even for the relatively low supersonic Mach number of a scramjet combustor (30-40% of the flight Mach), compressibility effects on turbulence production can be comparable to incompressible turbulence production. This analysis, based on theoretical arguments and limited experimental/numerical data from the available literature, indicates that the Strong Reynolds Analogy (a correlation between velocity and density fluctuations), initially developed for boundary layers, is also valid for unbounded supersonic mixing flows. This project proposes to experimentally verify the validity of the Strong Reynolds Analogy in a supersonic mixing unbounded flow by directly measuring density and velocity fluctuations utilizing two-point Focused Laser Differential Interferometry (2-FLDI). 2-FLDI is a proven low-cost technique that allows high-frequency, simultaneous, non-intrusive measurements of density and velocity fluctuations. The flow will consist of a simple planar jet from a pylon injector in a Mach 3 free stream. This work will also support STEM outreach through the development of a summer camp, and workforce development in hypersonics by supporting both graduate and undergraduate students. Findings from this work will also be incorporated into a graduate class on turbulent flows. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.