Investigations of High-Speed Civil Transport Inlet Unstart at Angle of Attack

Abstract

The unstart transient of a high-speed civil transport mixed compression axisymmetric inlet at Mach 2 and 2-deg angle of attack was investigated numerically by using a three-dimensional time-accurate Navier-Stokes solver. The Baldwin -Lomax algebraic turbulence model and an extrapolation uniform mass bleed boundary condition for the slot bleed were employed. It is observed that, when an angle of attack is imposed, the ow on the leeward side has a stronger compression than that at zero angle of attack. The strong compression reduces the Mach number upstream of the terminal shock and therefore makes the shock move upstream rst on the leeward side. The initial shock motion starts with the bifurcation of the terminal shock. The lower part of the split shock is stable because of the centerbody bleed, whereas the top part of the shock continues to travel upstream. When the terminal shock on the leeward side passes the bleed region, a separation is induced by the shock /boundary-layer interaction on the shoulder of the inlet centerbody, and the entire inlet is brought to unstart. The overall computed ow eld phenomena agree qualitatively with the experimental observations. Nomenclature M`= freestream Mach number P t`= freestream total pressure R c = radius at cowl leading edge T t`= freestream total temperature t c = characteristic time a = angle of attack Dr = grid point interval in radial direction 1 Dr 1 = (Dr 1 u t )/n D x = grid point interval in axial direction d = boundary-layer thickness on centerbody

Tradeoffs in Jet Inlet Design: A Historical Perspective

“…Typically, the phenomena in question are difficult to model because of their highly time-dependent (unsteady) nature. Examples are the self-sustained oscillations encountered by supersonic inlets operating in the subcritical flow regime [76,77] ("inlet buzz"), the instability of the terminal shock in high-speed mixed compression inlets [78,79] (inlet unstart), etc. Although there has been major progress in the numerical simulation of these phenomena, further increases in computing power will be needed before they will become part of the multidisciplinary design loops currently including calculations of pressure recovery, drag, steady distortion, etc.…”

Operation pattern classification of hypersonic inlets

“…Neaves and McRae [7] developed dynamic solution-adaptive gird algorithm introduced by Benson and McRae [8] and simulated the 3-D inlet unstart caused by a combustor perturbation. Zha [9,10] investigated unstart transient mechanism of a typical axisymmetric HSCT (high speed civil transport) inlet at angle of attack using CFD. Cox [11] presented several mechanisms of the hypersonic inlet unstart, including backpressure unstart, overcontraction unstart and angle of attack unstart.…”

“…So the classification of different hypersonic inlet operation modes, especial the classification of the inlet backpressure unstart/low Mach number unstart, is necessary to the unstart control of the hypersonic inlet. Unstart phenomena of the hypersonic inlet have been very active fields of research in last decades, there have been many investigations devoted to this subject [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Mayer and Paynter [5,6] used an Euler solver and simulated an axisymmetric inlet unstart due to the variation of freestream variables such as temperature, velocity and pressure.…”

Catastrophe Model for Supersonic Inlet Start/Unstart

“…Neaves et al [3] simulated the 3-D inlet unstart caused by a combustor perturbation. Zha et al [4,5] investigated the unstart transient mechanism of a typical axisymmetric inlet at different angles of attack. Cox et al [6] presented several mechanisms of supersonic inlet unstart, including backpressure unstart, overcontraction unstart, and the angle-of-attack unstart.…”