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Tangential blowing over the shoulder of a deflected rudder is applied on a vertical tailplane. For a large rudder deflection angle and without blowing the flow is mostly separated on the rudder. Three configurations are investigated in a numerical study with the aim to increase the side force coefficient. The first one is the baseline without blowing, the second one has a continuous full span slot and for the third one discrete slots are used. With sufficient blowing through the continuous slot the separation on the rudder can be removed completely while the separation extent is greatly reduced when using discrete slots. This is investigated for different sideslip angles. An approximately linear increase in the side force coefficient can be found until a sudden side force breakdown occurs. In a further study, the jet blowing velocity is varied. A smaller jet velocity leads to a smaller increase in the side force coefficient. Comparing the continuous and discrete slot configurations shows that for a similar increase in the side force coefficient a much smaller mass flow rate is needed for the discrete slots. However, for jet velocities below the sonic speed the increase in the side force coefficient is limited. It can only be increased by a larger slot extent in spanwise direction but this comes at the expense of an increase in the required mass flow rate.

Active flow control over the rudder shoulder of a vertical tail plane is applied to increase its side force coefficient. The rudder of the infinite span model is deflected. This leads without actuation to separated flow over the rudder. Several investigation are conducted. First a full-span constant blowing slot is used. With sufficient high jet velocity the flow on the rudder can be attached. By using in a next step several discrete slots, the required mass flow rate can be reduced for a similar increase in the side force coefficient. Using then pulsed blowing from the discrete slots is advantageous since the mass flow rate can be reduced. However, this is only true for quite small momentum coefficients. For cases with high side force coefficients requirements only the constant blowing approach is capable to achieve them, albeit at the correspondingly large mass flow rates and momentum coefficients.

On a swept vertical tailplane with infinite span tangential blowing over the shoulder of a deflected rudder is applied. For large rudder deflection angles the flow on the rudder is separated without blowing. A numerical study is conducted with the aim to increase the side force coefficient which might be required for a take-off condition if a one-sided engine failure occurs. With a continuous slot and sufficient mass flow rate the separation on the rudder can be reduced or avoided. It is shown that by using discrete slots this can be achieved for a similar side force coefficient gain with a smaller momentum coefficient. In addition the sweep angle of the incoming flow is varied showing a strong impact on the achievable side force coefficient. This is also true for the curvature of the rudder shoulder over which the jet is blown.

On a swept vertical tailplane with infinite span tangential blowing over the shoulder of a deflected rudder is applied. For large rudder deflection angles the flow on the rudder is separated without blowing. A numerical study is conducted with the aim to increase the side force coefficient. This could, for example, be required during take-off if the engine on one side fails, necessitating the compensation of a large yawing moment. If this criterion is critical for the sizing of the vertical tailplane, active flow control like tangential blowing could help to reduce the size of the vertical tailplane and thus save weight and fuel. With a continuous slot it is demonstrated that the separation on the rudder can be reduced or avoided. It is shown that using discrete slots this can be achieved with a smaller momentum coefficient. To analyze the effects of the discrete slots and their jets on each other and their effectivity with regard to the gain in side force coefficient a parameter study is conducted. The number of slots as well as the size of the slots in spanwise direction is varied and the impact of Jet velocity changes is also studied. In comparing the results for a constant increase in side force and constant slot size in spanwise direction the configuration with the smaller number of slots but a higher jet velocity proved to be the most effective one.

A numerical 2D investigation of a vertical tailplane airfoil using active flow control with tangential blowing over the rudder shoulder is conducted. The aim of the flow control application is to increase the maximum lift or side force, which can be created by the vertical tailplane, at critical flight conditions like the one-engine-inoperative failure case. In this case the rudder is highly deflected, leading to a large separation on the rudder without blowing. With constant tangential blowing at the rudder shoulder it was shown that fully attached flow can be achieved. To increase the efficiency, pulsed blowing is applied in the present study, leading to a similar increase in the lift coefficient at a reduced actuation mass flow rate requirement. Parameters like the blowing momentum coefficient and the dimensionless frequency are varied and the results are compared to those of the flow calculations with constant blowing. It is observed that pulsed blowing with a small momentum coefficient leads to a strong increase in the lift coefficient compared to constant blowing. The resulting lift increment depends on the dimensionless frequency selected.

A numerical 2D investigation of a vertical tailplane airfoil using active flow control with tangential blowing over the rudder shoulder is conducted. The intention of the flow control application is to increase the maximum lift or side force which can be created by the vertical tailplane at critical conditions like the one-engine-inoperative failure case. On the highly deflected rudder a large separation can be found without blowing. With tangential blowing it is shown that fully attached flow can be achieved. The flow simulations performed are based on the Reynolds-averaged Navier-Stokes equations. The parameters momentum coeffi�cient, slot height and angle of attack of the oncoming flow are varied to assess sensitivities and the influence on the results. Furthermore, the influence of a geometric detail in the vicinity of the slot exit is investigated, namely the existence or omission of a step behind the slot exit. Finally, the influence of the turbulence model is studied where besides the Spalart and Allmaras turbulence model with rotational and curvature correction (SARC) also the SAO and RSM turbulence models are applied.

Problems were posed and solved concerning the aerodynamic computation of the flow past an airfoil with an active boundary layer control device used to prevent flow separation. A moving wall, suction, or tangential blowing in the boundary layer was used as a flow control device. The turbulent boundary layer was computed by directly solving the boundary layer equations using an implicit difference scheme with adaptive grid generation and the determination of the computational domain size. A software code was developed, and numerical simulations were performed taking into account the energy costs related to the flow control device. The numerical results showed that the active flow control devices can be used to prevent flow separation. © Pleiades Publishing, Ltd., 2009.