Unstart dynamics of hypersonic Busemann inlet at non-zero angles of attack

Abstract Unstart dynamics are experimentally investigated in a streamtraced hypersonic inlet at angles of attack, $$\alpha = -5^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>α</mml:mi> <mml:mo>=</mml:mo> <mml:mo>-</mml:mo> <mml:msup> <mml:mn>5</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:mrow> </mml:math> , $$\alpha = 0^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>α</mml:mi> <mml:mo>=</mml:mo> <mml:msup> <mml:mn>0</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:mrow> </mml:math> and $$\alpha = 3^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>α</mml:mi> <mml:mo>=</mml:mo> <mml:msup> <mml:mn>3</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:mrow> </mml:math> . High repetition pressure field imaging and external shock structure imaging are performed to time resolve the unstart shock foot motions and shock train dynamics, which provide mutually evaluating and complementary information about the unstart dynamics. Two distinct unstart responses, referred to as a "weak" and "strong" response, are obtained at low and high back pressure settings. During a weak response, the unstart leading shock was disgorged from the internal passage but oscillated near the cowl closure, with supersonic flow present in the vicinity of the cowl. During a strong response, the unstart shock train is disgorged from the inlet internal passage and the unstart leading shock oscillates in the close vicinity of the inlet leading edge. An entirely subsonic flow entered the inlet internal passage during this response. The influence of angle of attack on the shock dynamics is then evaluated by tracking the unstart leading shock foot. Critical differences were observed in the unstart shock motions and shock velocities between the weak and strong responses for a given angle of attack and for a given response between the different angles of attack. Due to these differences, the unstart duration for a strong response, increased from approximately 11 ms to 14 ms for $$\alpha = -5^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>α</mml:mi> <mml:mo>=</mml:mo> <mml:mo>-</mml:mo> <mml:msup> <mml:mn>5</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:mrow> </mml:math> to $$\alpha = 3^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>α</mml:mi> <mml:mo>=</mml:mo> <mml:msup> <mml:mn>3</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:mrow> </mml:math> . The peak unstart shock speed for $$\alpha = -5^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>α</mml:mi> <mml:mo>=</mml:mo> <mml:mo>-</mml:mo> <mml:msup> <mml:mn>5</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:mrow> </mml:math> is approximately 20% higher when compared to $$\alpha = 3^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>α</mml:mi> <mml:mo>=</mml:mo> <mml:msup> <mml:mn>3</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:mrow> </mml:math> . A new velocity scaling based on the mean inflow velocity at the inlet throat plane makes a better collapse of the peak shock velocity.