Investigation on control of cavity flow by bleed near ... Web viewand the unsteady impingement of the shear layer on the rear wall produces pressure waves that travels inside the cavity

Visit techris.in/tzx to get full details of this project idea

Visit techris.in/tzx to get full details of this project

Investigation on control of cavity flow

by bleed near trailing edge

0.1 Introduction

Cavities generally exist in the form of landing gear wheel well (Fig 1) and weapon bay (Fig 2) in air

crafts. The grazing flow over the cavity tends to produce high magnitudes of oscillation at a frequency

that depends on so many factors such as cavity dimensions, free stream Mach number, boundary layer

status at cavity leading edge.

The separated shear layer from the leading edge grows and the disturbances are amplified due to

Kelvin Helmholtz instability, and the shear layer is wrapped into vortices as shown in fig 3 and the

unsteady impingement of the shear layer on the rear wall produces pressure waves that travels inside

the cavity toward leading edge. Upon reaching the leading edge, the pressure wave energises the

leading edge and completes the feedback loop which leads to self sustained oscillations (Fig 4).

Without control this high amplitude self sustained oscillations (Upto 170 dB) (Fig 5)can damage the

sensitive electronic equipments or can affect the weapon release from the air craft (Fig 6). The noise

radiated from the cavity need to be controlled.

Among passive, open and closed active control techniques, passive control has the advantages over

other control techniques in the form of simple, easy to install and maintain. They dont need any external

energy input.

This study aims to apply bleed near trailing edge to releive the higher unsteady pressures. The

schematic of the bleed is shown in fig 7. The configurations will be tested at a freestream Mach number

of 0.8.

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0.2 Test Matrix

Mach number L/D

0.8 5

0.3 Flow field variables to be analyzed

• Mean Pressure

• Unsteady pressure

• Oscillation amplitude

• Velocity Field

2



0.4 Images

Figure 1: Wheel well of an aircraft, from www.marcodebiasi.net

Figure 2: Weapon bay of a combat aircraft, from www.defence.pk

3



Figure 3: Schlieren image of flow over cavity from Kegerise[1]

Figure 4: Schematic of flow over cavity

Figure 5: Typical spectra of cavity flows, from [2]

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Figure 6: Effect of control on store trajectory. High-speed instantaneous shadowgraphs, showing the favorable effect of control on store trajectory, from [2]

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Figure 7: Schematic of bleed in cavity ”

5



References

[1] M. A. Kegerise, An experimental investigation of flow-induced cavity oscillations. PhD thesis,

Syracuse University, 1999.

[2] L. N. Cattafesta, Q. Song, D. R. Williams, C. W. Rowley, and F. S. Alvi, “Active control of flow-

induced cavity oscillations,” Progress in Aerospace Sciences, vol. 44, no. 7, pp. 479–502, 2008.

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Investigation on control of cavity flow by bleed near ... Web viewand the unsteady impingement of the shear layer on the rear wall produces pressure waves that travels inside the cavity