Confined supersonic mixing layers: A computational investigation of instability and mixing enhancement

Thesis/Dissertation · Mon Jan 01 04:00:00 EST 1990

OSTI ID:5894863

Hu, F Q

Hydrodynamic instability of a compressible shear mixing layer plays a very important role in controlling and promoting the mixing processes in supersonic combustion problems. At supersonic convective Mach numbers, the natural mixing rates of the shear layer are observed to be very small. The linear spatial instability problem of a supersonic shear mixing layer inside a rectangular channel is solved. A systematic way of calculating and classifying all the normal modes is developed. It is demonstrated that a vortex sheet at high supersonic convective Mach number, neutrally stable when unconfined, becomes unstable when confined. Extensive numerical computations indicate that two classes of unstable supersonic instability waves can be identified. In addition to unstable waves, two families of neutral acoustic waves can also be identified. The characteristics of the unstable waves as well as the neutral waves are determined. It is concluded that the new supersonic instabilities found in this study are the dominant instabilities of a confined mixing layer at high supersonic convective Mach numbers. Thus, they are very relevant to the supersonic combustion problem. The possibility of enhancing the rate of supersonic mixing by means of a periodic Mach wave system is explored. The stability of the periodic basic flow is analyzed numerically by the Floquet theory and the spectral-collocation method. The convergence of the numerical solutions is discussed. New secondary instabilities of the shear layer induced by the periodic Mach waves are found computationally. The growth rate of the new instabilities is found to vary nearly linearly with the ratio of the wavy wall amplitude to the wave length. Therefore, it is a potentially promising scheme for the enhancement of supersonic mixing.

• Research Organization: Florida State Univ., Tallahassee, FL (USA)
• OSTI ID: 5894863
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400800* -- Combustion
Pyrolysis
& High-Temperature Chemistry
CHEMICAL REACTION KINETICS
COMBUSTION KINETICS
COMPRESSIBLE FLOW
CONFINEMENT
FLUID FLOW
KINETICS
LAYERS
MACH NUMBER
MIXING
REACTION KINETICS
SOUND WAVES
STABILITY
SUPERSONIC FLOW
VELOCITY