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Control of air-intake lip separation using air-jet vortex generators

Williams, M. J. (2004). Control of air-intake lip separation using air-jet vortex generators. (Unpublished Doctoral thesis, City, University of London)


Air vehicle air intakes are required to operate across a range of flow conditions, the design criteria for which are not necessarily complementary. It is proposed that flow control, in particular the novel application of Air-Jet Vortex Generators (AJVGs), can be used to enhance the off-design performance of an air intake system allowing a design focused heavily toward a particular design point.

A review of the open literature suggests a noticeable benefit of flow control in optimising intake performance by improving total-pressure recovery and reducing total-pressure distortion. The practicalities of installation, however, have rendered most studies only of academic interest. Vane vortex generators (VVGs) provide an improvement at only a small range of flows for which they are specifically designed. They also exhibit a large off-design penalty in the form of a parasitic pressure loss in the propulsion stream tube. Tangential blowing requires a relatively large portion of the intake mass-flow and is also inflexible to different operating regimes making it unacceptable. The more traditional form of intake flow control in the form of variable geometry is expensive and heavy but efficient if a Mach 2 plus capability is desired.

In a novel application, AJVGs have been proposed for control of flow separation at the intake lip. The large operating envelope of AJVGs, particularly with regard to local flow direction, small mass-flow requirement and negligible off-design penalty make AJVGs potentially unrivalled in this application. Maximum benefit could be obtained by using an existing intake leading edge, ice-protection system, and this will potentially save installation weight and cost. In this study, AJVGs have been shown to increase the angle of incidence for which separation occurs on an intake lip by 10 degrees using less than 0.5% of total intake mass flow.

A computation modelling technique has been developed which saves computational expense in the design of an AJVG installation by using a relatively simple boundary condition at the intake surface to model the jet exit. Wind tunnel tests on an installation designed using this method have validated its applicability. Computational fluid dynamics has been used to expand the test envelope to mass flows not obtainable
experimentally, demonstrating the validity of AJVGs for controlling lip separation at the extremes of the operating envelope.

This demonstration of AJVG technology is applicable to a range of different aircraft and engine types; in particular, modem military air-vehicles driven by low-observable design considerations that are penalised by small radius lip intakes.

The development of a methodology for successful intake flow control comes from the understanding that intake lip separation, certainly for practical applications, is three- dimensional in nature.

Publication Type: Thesis (Doctoral)
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
T Technology > TL Motor vehicles. Aeronautics. Astronautics
Departments: School of Science & Technology > Engineering > Mechanical Engineering & Aeronautics
School of Science & Technology > School of Science & Technology Doctoral Theses
Doctoral Theses
[thumbnail of Williams thesis 2005 PDF-A.pdf]
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