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Abstract:
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The dynamics of the unstart process in inlet / isolator models mounted to the floor of a Mach 5 wind tunnel are investigated experimentally . The most extensively studied model has an inlet section that contains a 6 -degree compression ramp and the isolator is a rectangular straight duct that is 25 .4 mm high by 50 .8 mm wide by 242 .3 mm long . Unstart is initiated by raising a motor -driven flap that is located at the downstream end of the isolator section . Unstart proceeds with the formation of a shock system that propagates upstream at an average velocity of about 37 m /s (in the lab frame of reference ) , which is five percent of the freestream velocity . Unstart is seen to be associated with strong shock -induced separation that leads to reverse flow velocities up to about 300 m /s as measured by PIV . Both the schlieren imaging and PIV data suggest the dynamics and flow structure of the unstart process are dependent on inlet geometry . Furthermore , the PIV data indicate the unstart process to be highly three -dimensional . Finally , tripping the ceiling and sidewall boundary layers was seen to result in slower unstart processes . In addition , results are presented for 0 -degree (no inlet ) and 8 -degree inlet / isolator models . In the 0 -degree model , the experimental data show that the flow structure and propagation velocities of the unstart shock system are much more constant than those measured in unstart events with an inlet . In addition , an increased inlet compression angle appears to result in an increased unstart propagation velocity in the isolator . This is possibly related to the fact that with an increased compression ramp angle , the unstart shock system propagates against a lower momentum opposing flow . Furthermore , the inlet geometry is also seen to affect the flow that follows the unstart process . Experiments were also conducted with each of the three inlets attached to a shortened isolator . The short -isolator experiments showed it was possible to form a stable high -compression shock system in the isolator by raising the flap . This was not the case in longer isolator tests . |