A novel optimised design using slots for flow control and high-lift performance of UCAVs

Ali, U

Abstract

In this study, two UCAV planforms are considered based around generic 40° edge-aligned configurations. One configuration has a moderate leading and trailing edges sweep of Λ = 40°, while the other configuration is highly swept with a leading-edge sweep of Λ = 60° and trailing edges sweep of Λ = 40°. The objectives of the present study on UCAV configurations are two-fold: first to predict aerodynamic performance particularly the maximum-lift characteristics of two flying wing planforms; second to control the flow by inserting leading-edge and chordwise slots and analysing the viscous flow development over the outboard sections of a flying-wing configuration to maximise the performance of control surfaces.


The first part is demonstrated using a variety of inviscid Vortex Lattice Method (VLM) and Euler, and viscous CFD Reynolds Averaged Navier-Stokes (RANS) methods. The computational results are validated against experiment measured in a wind tunnel. The VLM predicts a linear variation of lift and pitching moment with incidence angle, and substantially under-predicts the induced drag. Results obtained from RANS and Euler agree well with experiment.

For the second part, a novel optimised design using chordwise slot is implemented on a highly swept Unmanned Combat Air Vehicle (UCAV) configuration to maximise the lift over trailing edge control surfaces. More airflow over the control surfaces will result in enhanced lateral control of the air vehicle at medium to high angles of attack. Four parameters describing the chordwise slot are identified for the numerical optimisation. They are: location, width, length and angle of trajectory of chordwise cavity relative to freestream. The angle of trajectory of chordwise slot is measured with respect to the trailing edge of the air vehicle. The results of CFD optimisation are compared with a clean configuration and verified with experiment. The configuration with chordwise slot has shown higher mass flow rate over the control surfaces of the air vehicle in comparison to baseline clean configuration. It is demonstrated that higher mass flow rate results in higher lift. Leading-edge slot method is considered, but the method improves the flow control for the low angles of attack regime, and is found to be ineffective for a highly-swept UCAV configuration at medium to high angles of attack.

Citation

Ali, U. (in press). A novel optimised design using slots for flow control and high-lift performance of UCAVs. (Thesis). University of Salford

• Thesis Type: Thesis
• Acceptance Date: Mar 29, 2019
• Deposit Date: Apr 5, 2019
• Publicly Available Date: Apr 5, 2019