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Three-dimensional shock control bumps have long been investigated for their promising wave drag reduction capability. However, a recently emerging application has been their deployment as 'smart' vortex generators, which o↵set the parasitic drag of their vortices against their wave drag reduction. It is known that 3D SCBs produce streamwise vortices under most operating conditions; however, there have been very few investigations which have aimed to specifically examine the relevant flow structures. In particular, the strength of the vortices produced as well as the factors influencing their production are not well known. This paper uses a joint experimental and computational approach to test three di↵erent SCB shapes, categorising their flow structures. Four common key vortical structures are observed, predominantly shear flows, although all bumps also produce a streamwise vortex pair. Both cases with and without flow separation on the bump tails are scrutinised. Finally, correlations between the strength of the main wake vortices and pressure gradients at various locations on the bumps are assessed to investigate which parts of the flow control the vortex formation. Spanwise flows on the bump ramp are seen to be the most influential factor in vortex strength.

The vortical wake structure produced by a three-dimensional shock control bump (SCB) is thought to be useful for controlling transonic buffet on airfoils. However, at present the vorticity produced is relatively weak and the production mechanism is not well understood. Using a combined experimental and computational approach, a preliminary investigation on the wake vorticity for different bump geometries has been carried out. The structure of the wake for on-and off-design conditions are considered, and the effects on the downstream boundary layer demonstrated. Three main vortical structures are observed: a primary vortex pair, weak inter-bump vortices and shear flow in the lambda-shock region. The effect of pressure gradients on vortex strength is examined and it is found that spanwise pressure gradients on the front section of the bump are the most significant parameter influencing vortex strength. Nomenclaturec = Airfoil chord length H ≡ δ * θ = Incompressible boundary layer shape factor M ∞ = Freestream Mach number Re χ ≡ ρU∞χ µ = Reynolds number based on length scale χ u ≡ (u, v, w) = Stream-wise, tunnel floor-normal velocity components [m/s] u ∞ = Free-stream velocity x, y, z = Stream-wise, tunnel floor-normal, tunnel span-wise coordinates [mm] x s = Streamwise shock position relative to bump tip [mm] α = Angle of attack [ • ] δ = Boundary layer thickness (measured to 99% freestream velocity) [mm] δ * = Incompressible boundary layer displacement thickness [mm] θ = Incompressible boundary layer momentum thickness [mm] λ c = Complex eigenvalue of velocity gradient tensor ∇u µ = Dynamic viscosity [kg/(ms)] ρ = Density [kg/m 3 ] ψ ≡ tan −1 v u = Vertical flow angle [ • ] ω x = Streamwise component of vorticity [s −1 ] * PhD student, AIAA student member.

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