The relationship between surface geometry and transonic intake performance during off-design climb

The design of slimmer, shorter gas-turbine nacelles supports lower emissions in civil aviation. However, these designs often have a stronger shock on the windward front-lip of the intake during off-design climb, producing a severe shock wave--boundary-layer interaction (SBLI) that greatly increases the ingested incompressible boundary-layer displacement thickness, δ_i^*, and shape factor, H_i. Simulating these conditions without validation is challenging, and poor optical access has inhibited observations of how intake surface geometry influences the SBLI. This thesis investigates the relationships between intake surface geometry, the impact of the transonic SBLI, and intake performance during off-design climb with a quasi-two-dimensional (Q2D) experiment that represents flow over the lower-lip of a civil intake. Design of Experiments was applied to create a 2⁴ factorial investigation of highlight curvature, surface-curvature distribution, diffuser shape, and mass flow rate. The facility supports high-speed schlieren imaging, pressure-sensitive paint, laser Doppler velocimetry and oil-flow visualisation. A Q2D transonic SBLI formed on the intake front-lip in each test-case, and the test-cases have shock strengths in the range of M_s = 1.14 - 1.64 and an order of magnitude range in δ_i^*. Importantly, this shows that intake surface geometry influences performance as significantly as other studies conclude for changes in overall intake geometry. Intakes with large highlight curvature had minimal δ_i^* and little sensitivity to changes in mass flow rate or the surface-curvature distribution, which demonstrates that highlight curvature is the key geometric parameter in determining intake performance at off-design climb. Once the front-lip shape is optimised to a small nose-radius (equivalent to large highlight curvature) and generally thin profile, the diffuser shape becomes an important consideration. An "s-shaped" diffuser with a large peak surface angle promotes minimal δ_i^*. Intake performance generally remains favourable provided that M_s<1.45, which corresponds to the onset of well-established separation, and worsens non-linearly as shock strength exceeds this threshold. Further analysis identified two key parameters that together characterise the impact of the SBLI on intake performance, \(APG\), which is the pressure gradient between the end of the shock jump and the measurement of δ_i^*, and a newly-defined parameter, L^*, which is similar to the supersonic length-scale in an attached transonic SBLI. Plotting \(APG\) and L^*, or \(APG\) and δ^*_i, collapses the test-cases onto linear trends, where intake performance scales continuously between the smallest and largest values of L^*. The intake performs with minimal δ^*_i when the SBLI is effectively-separated, M_s=1.32, because these interactions have minimum L^*, while weaker or stronger interactions worsen this performance. This analysis is supported by validated multivariate response surfaces that model the relationships between intake surface geometry, the SBLI and intake performance. Overall, the models and conclusions in this thesis guide the design of an intake surface that maintains fan-intake compatibility, which supports the development of shorter and slimmer nacelles. Further work should consider other off-design conditions, such as high-power crosswind.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• O'Pray, Connor

Advisor dc:contributor.advisor

• Babinsky, Holger

• SBLI
• shock wave--boundary-layer interaction
• Intake performance
• Gas turbine aerodynamics
• Experimental
• Design of Experiments
• Schlieren
• Pressure sensitive paint
• Laser Doppler velocimetry
• Oil flow visualisation
• Transonic
• Boundary-layer displacement thickness
• Highlight curvature
• Leading-edge radius
• Diffuser
• Intake design

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/5acf7ff2-2fc0-47b8-a566-ffe5ceecc27b/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

Author Identifier

0000-0001-6748-2460

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/381857