Recent interest in supersonic combustion (scramjets) and noise reduction for the high speed civil transport (HSCT) plane prompted renewed research in supersonic mixing processes and means to control them. The scramjet propulsion concept requires rapid mixing between fuel and air in order to minimize the size of the combustor and affect the performance of the entire vehicle system. Also, accelerated mixing of exhaust plumes with coflowing air has been shown to lead to jet noise reduction. Other examples of technological applications requiring control of mixing in compressible flows include thrust augmenting ejectors, thrust vector control, metal deposition, and gas dynamic lasers. The technological challenge of mixing enhancement in compressible flows stems from the inherently low growth rates of supersonic shear layers. Many mixing augmentation methods employed efficiently in sub­ sonic flows failed to work at elevated Mach numbers, and some were inefficient because they were utilized outside their effective range. Never-

Mixing enhancement in supersonic free shear flows

1. Introduction 2. Theoretical background 3. High temperature gas dynamics and hypersonic effects 4. Cycle analyses and energy management 5. Inlets and nozzles 6. Supersonic combustion processes and characteristics 7. Testing methods and wind-tunnels 8. Computational fluid dynamics methods and solutions for high speed reacting flows.

The Scramjet Engine: Processes and Characteristics

An experimental investigation of the vortical and turbulent structure in a free shear lager downstream of a lobed mixer has been conducted. Pulsed-laser sheet flow visualization with smoke and three-dimensional velocity measurements with hot-film anemometry were obtained for a lobed-mixer configuration and a baseline, planar configuration. Laminar and turbulent initial boundary-lager conditions were documented for both cases. The main result of this investigation is that a new vortex structure was confirmed to exist for the lobed mixer in addition to the well-known streamwise vortex array, consistent with the work of Manning

Vortical and turbulent structure of a lobed mixer free shear layer

The Scramjet Engine: List of Acronyms

A review of rocket-airbreathing combined-cycle propulsion systems for Earth-to-orbit applications is presented. Rocket-based combined-cycle (RBCC) engines take advantage of the synergistic interactions between the rocket and the airbreathing elements of the engine and the use of high-specie c impulse cycles to yield a mission-averaged specie c impulse that is higher than all-rocket technology can provide. An overview of the multimode operation is given, along with a review of both experimental and modeling work that has been done on this class of engines. Selected issues involved with these engines are discussed. These include engine/vehicle integration, e ow-path design for multimode operation, fuel selection, mixing enhancement and afterburning in rocket-ejector mode, thermal choking, and e ameholding. RBCC propulsion is becoming recognized as a promising technology for achieving a signie cant reduction in the cost of delivering payload to orbit.

Combined Rocket and Airbreathing Propulsion Systems for Space-Launch Applications

Forced mixer lobes in augmentor primary ejectors obtain a 100-percent increase in pumping over conventional design, together with nearly complete mixing in very short mixing ducts, through the generation of large scale axial vorticity in the mixing duct. The vorticity causes rapid mixing of the primary and secondary flows with low losses; since mixing length is minimized, wall friction losses are reduced, allowing more secondary flow to be pumped for a given total pressure in the primary flow. Analytical results are presented that are judged to have significant implications for future ejector test work.

Bruce Kl. Morin

Papers

Forced mixer lobes in ejector designs

Forced mixer lobes in ejector designs