|M.Sc Thesis||Department of Aerospace Engineering|
|Supervisor:||Assoc. Prof. Rimon Arieli|
|Full Thesis text|
A numerical investigation is presented for a two-dimensional shock control bump (SCB or bump) at transonic speeds. The influence of the bump on drag in comparison to the clean airfoil is evaluated. The numerical procedure is based on Reynolds Averaged Navier Stokes (RANS) simulations with several turbulence models which are validated by a comparison to known experimental and numerical results.
Parametric study of bump's shape, height, and location is presented and their effect on drag reduction at transonic speeds is assessed. Two types of SCB are placed on two airfoils, NACA 0012 symmetrical airfoil and DRA 2303 supercritical one. An optimal bump is found for each airfoil, defining its shape, height and location along the chord. In both cases considerable drag reduction has been achieved, of up to 14%, owing to a λ-shock structure produced on the NACA 0012 airfoil and a bifurcated shock structure on the DRA 2303.
Flow field analysis has shown that there is a deceleration of the flow on the upslope of the bump accompanied by a pressure rise which leads to both a weaker shock and smaller pressure losses. It is also demonstrated that the optimal bump for the supercritical airfoil causes an additional bifurcated shock instead of the weak normal shock for the NACA case due to a small acceleration on the inflection point of the bump.
The effect of the selected bump on aerodynamic coefficient at off-design conditions is studied, and found that the airfoil-bump configuration outperforms the clean airfoil above design conditions (considering angle of attack and Mach number). It is also demonstrated that there is a significant potential increase in range-factor at the design point. The maximum aerodynamic efficiency increases considerably, and moves to a higher incidence angle, closer to the design point.
The effect of bump on shock buffet is studied as part of the unsteady solution. The influence on buffet onset, frequency, amplitude, shock travel and location of center of pressure are presented. The influence on buffet onset is not conclusive since the results differ extensively for the two airfoils. It is shown, however, that the bump has a stabilizing effect on the developed buffet, when positioned at close proximity behind the shock location. Shock location in the unsteady solution is defined as the location just before onset.