Optical Investigation of Flow Field Generated by Normal Shock Propagating into a Rectangular Duct with Irregular Walls.
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OHIO SCHOOL OF ENGINEERING
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An optical study of flow field behind a normal shock wave propagating into a rectangular duct with irregular walls was conducted in the AFIT 8 in x 4 in x 20 ft air-air shock tube. Attenuation behavior of the normal shock was also studied. An average upstream Mach number of 1.59 was maintained for all runs. A total of five wall shapes designated as A, B, C, D and E were fabricated and analyzed. Model A, a straight section, served as reference for comparative study of other models. Models B, C and D had identical wave lengths, amplitudes and maximum and minimum flow areas but their ramp angle 0 was 30 deg, 60 deg and 90 deg, respectively. Model E had a saw tooth design and all the other geometrical parameters except the wavelength and the ramp angle were similar to Models B thru D. The wavelength for Model E was half the value of other models and its ramp angle was 63 deg. Disturbance attenuation was determined by measuring its speed across consecutive pairs of pressure transducers located at known distances along the entire length of the test section. Time interval counters measured the time lapse between transducers. Comparative study of all models revealed that disturbance attenuation depends upon the shape of the iregular wall and the two most significant factors in this regard are the ramp angle and the wave length. A higher ramp angle leads to more abrupt area reduction and provides greater attenuation. Shorter wave length provides more inrregularities per unit length, which results in considerable improvement in attenuation phenomenon. Model D, 0 - 90 deg is branded as the most effective design in the present study.
- Fluid Mechanics