Browsing by Author "Kuppa, Subrahmanyam"

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    End plate gap effects on a half-wing model
    Kuppa, Subrahmanyam (Virginia Tech, 1987-04-15)
    Differences in the aerodynamic performance data obtained at different test facilities were observed for the Wortmann FX-63-l37 airfoil. Earlier investigations found that the size of the hysteresis loop was affected by the tunnel environment and that single strut mounting of a three dimensional wing model interfered negligibly with the wing. Theoretical and experimental evaluations of a half wing model mounted with an end plate gap were done. Vortex panel method was used in the theoretical evaluation. The results from this indicated an effect of reduced aspect ratio with increase in end plate gap size. Tests were conducted in the VPI Stability Tunnel at low Reynolds numbers for different gap sizes including sealed gap. Results from the experiments showed that even very small gaps produce substantial changes in zero lift angle of attack (αu) and the change in αu, was reduced as Reynolds number increased. Sealed gap test results did not show such a behavior. Flow visualization of the flow through the gap showed a significant flow through the gap even at very low Reynolds number and small gap size.
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    Visualization and velocity measurement of unsteady flow in a gas generator using cold-flow technique
    Kuppa, Subrahmanyam (Virginia Polytechnic Institute and State University, 1989)
    Modeling of internal flow fields with hot, compressible fluids and sometimes combustion using cold flow techniques is discussed. The flow in a gas generator has been modeled using cold air. Experimental set up was designed and fabricated to simulate the unsteady flow with different configurations of inlet tubes. Tests were run for flow visualization and measurement of axial velocity at different frequencies ranging from 4 Hz to 12 Hz. Flow visualization showed that the incoming flow was a complex jet flow conformed to a cylindrical enclosure, while the outgoing flow resembled the venting of a pressurized vessel. The pictures show a complex flow pattern due to the angling of the jet towards the wall for the bent tube configurations and straightened flows with straight tube and other configurations with straighteners. Velocity measurements were made at an inlet Re of 8.1 x 10⁴ based on maximum velocity and inlet diameter using a single sensor hot wire anemometer at several locations in the plane of the inlet tube at 4 Hz, 8 Hz and 12 Hz for the straight tube and bent tube inlet configurations. The axial velocity near the entrance showed a strong component of the forcing frequency. Phase averaged mean velocities were observed to be well defined during charging and diminished during venting inside the cylinder. The jet flow penetrated most for the 4 Hz and least for the 12 Hz case. For the straight tube inlet comparison with a steady flow measurement of sudden expansion flow showed a qualitative similarity of the mean axial velocity distribution and centerline velocity decay during the charging phases. For the bent tube inlet case the contour plots showed the flow tendency towards the wall. Two cells were seen in the contours for the 8 Hz and 12 Hz cases. The deviation of the point of occurrence of maximum velocity in a radial profile was found to be about 6.5°. Entrance velocity profiles showed symmetry for the straight tube inlet while were skewed for the bent tube inlet. Contour plots of the phase averaged axial turbulence intensity for bent tube cases showed higher values in the core and near the wall in the region of impingement. Axial turbulence intensity measured for the straight tube case showed features as observed in an axisymmetric sudden expansion flow.