Forced Oscillations in a Mixed-Compression Inlet at Mach 3.5 for Pulse Detonation Engine Systems

[+] Author and Article Information
Venkata Nori, Nelson Lerma, Jonas Gustavsson, Corin Segal

Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida 32611

Rene Fernandez

 NASA Glenn Research Center, Cleveland, Ohio 44135

J. Fluids Eng 128(3), 494-506 (Oct 21, 2005) (13 pages) doi:10.1115/1.2174061 History: Received March 31, 2004; Revised October 21, 2005

The effects of oscillatory backpressure on the air induction system for pulse detonation engines were examined for a two-dimensional, mixed-compression configuration at a freestream Mach number of 3.5. The pressure perturbations at the diffuser exit were produced by injecting air through four ports located at the corners of the exit cross section. The frequency, coupling of the ports and airflow rates through the ports were varied, simulating the operation of detonation tubes. A terminal normal shock in the diffuser oscillated in the excited inlet, causing large pressure fluctuation amplitudes at some locations. Large injection mass flows resulted in inlet flow oscillations throughout the inlet, increased the spillage, yet did not cause inlet unstart.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

PDE inlet with injection block mounted at the back. Rear side view of the inlet showing its main components.

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Figure 2

Shock structure as calculated from oblique shock relations with terminal normal shock. Estimated regions of separated flow are shaded. All dimensions are in mm.

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Figure 3

(a) Inlet schematic showing the location of wall static pressure taps and bleed plenums along with the definitions of L=135mm and h=9mm used for axial and vertical normalization, respectively. (b) Top view schematic of the inlet ramp showing static tap and boundary layer bleed locations. (c) Static tap streamwise locations. All dimensions are in millimeters.

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Figure 4

Front view of the exit injection block with the stagnation pressure rake embedded in it with the probe designations. Flow is into the page.

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Figure 5

(a) Rear view of the exit injection block with the port designations and the injection configurations below. Flow is out of the page. 1. Cowl coupling: Ports (1,2) inject air. 2. Ramp coupling: Ports (3,4) inject air. 3. Side coupling: Ports (1,3) inject air. 4. Cowl-ramp coupling: Ports (1,2) and (3,4) inject air, 180deg out of phase. 5. Side-side coupling: Ports (1,3) and (2,4) inject air, 180deg out of phase. 6. Ninety degree phase coupling: Each port injects air at 90deg out of phase with the neighboring ports. (b) Air injection system schematic.

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Figure 6

Mean wall static pressures normalized by the wind tunnel stagnation pressure with no air injection

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Figure 7

Schlieren images. (a) Entire flow field in the inlet without injection. The shocks generated by the two wedges are visible along with the separation bubble on the second wedge, which produces the expansion associated with reattachment. (b) Close-up view of the terminal shock structure and the separation induced both on the cowl and the ramp.

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Figure 8

Comparison between the ramp and the cowl mean normalized static pressures. (a) Noninjection case. (b) Injection case.

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Figure 9

Plots for comparing the excited and the unexcited inlet, for Minj=20% and f=5Hz for the 90deg phase coupling case. (a) Mean normalized wall static pressure. The error bars show the ±×RMS fluctuation amplitude. (b) Normalized exit stagnation pressure. (c) Normalized wall static pressure fluctuation.



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