The environmental impact of conventional civil aircraft can be reduced by minimising the diameter of the gas turbine nacelle. This nacelle has less wetted-area and less projected-area so aircraft drag is reduced during the cruise flight-phase. However, this design approach requires a slimmer intake which can cause lower propulsive efficiency during the climb flight-phase. During climb, the lower-portion of the intake experiences a large massflow and large local angle-of-attack so the flow accelerates to form a supersonic region on the interior surface. A slim intake shape may increase the peak Mach number within this supersonic region. Consequently, this region terminates with a stronger shock wave-boundary-layer interaction (SBLI) which can worsen boundary-layer (BL) parameters and BL separation in the subsonic diffuser. These parameters have crucial influence in engine operation because this location is situated immediately upstream of the transonic fan.
There is an absence of experimental data on this transonic SBLI despite its importance in calculating the climb-phase performance of slim intakes. This ignorance prevents the validation of computations which are extensively used in industry for intake design; such validation is required because the applicability of these computations is somewhat unestablished for flows that are unsteady, viscous and transonic. So, the design of slim intakes is presently unfeasible in civil aerospace.
This research project supports the design of slim intakes that have minimal boundary-layer separation during the climb-phase by investigating the following research question. What is the influence of the intake's interior-surface geometry on the SBLI and subsequent BL separation which forms during the climb-phase?
The research question is investigated experimentally with a quasi-two-dimensional (Q2D) approach which simplifies the experimental configuration and facilitates optical instrumentation. This approach produces data with high spatial-resolution and corresponds to the centre-plane flow adjacent to the lower inner-surface of a real intake. The highly-resolved two-dimensional data can accurately characterise the relation between geometry, shock formation and BL separation. This dataset can validate the centre-plane of three-dimensional (3D) computations which subsequently is indicative of the entire 3D flowfield.
This experimental project investigates the behaviour of a transonic SBLI on curved surfaces in the presence of an adverse pressure-gradient. Three geometric parameters are varied in order to understand their influence on the SBLI: the leading-edge radius-of-curvature, surface-curvature distribution of the intake interior-surface, and the subsonic diffuser profile. The geometric parameter range is an extensive design space that encompasses both conventional and slim intakes. A Design of Experiments methodology makes it feasible to investigate this extensive design space
Approach
Define intake profiles of geometries within the design domain of traditional and slim intakes.
Produce an experimental campaign that investigates this design domain.
Produce an experimental test-piece assembly that integrates into an existing supersonic wind tunnel and satisfies the campaign.
Adapt an existing supersonic wind tunnel to facilitate the use of experimental instrumentation methods. Instrumentation methods shall be time-correlated.
Collect and analyse experimental data.
Novel engineering content
Contributes to the EPSRC research area "Fluid Dynamics and Aerodynamics".
This research characterises the influence of surface-curvature on a transonic SBLI with particular focus on shock strength BL separation and severe unsteadiness.
This research programme characterises the relationship between different adverse pressure-gradients and transonic SBLIs.
The application of time-correlated single-point and optical measurements of SBLIs to a Q2D intake under climb-phase conditions