Tangential Leading Edge Blowing Research Articles

Experimental investigation of twin-fin buffeting and suppression

An investigation has been undertaken to study the characteristics of vertical fin buffeting for various twin-fin configurations at high angles of attack. Tests were performed in the 2.1 X 1.5 m low-speed wind tunnel at the University of Bath, using three 60-deg cropped generic delta wings of 0.5-m span. To sense unsteady pressures at the fin surface, a rigid fin instrumented with miniature pressure transducers was fabricated, whereas a flexible fin of similar planform and size was used to measure the buffeting response. It was found that the fin configurations were typified by two maximum buffeting conditions. The first peak response was effectively a vortex/fin interaction in isolation, whereas the second peak response was the result of a vortex shear-layer oscillation between the fins. A novel flow concept (tangential leadingedge blowing) was then used to decrease the levels of buffeting response for all fin configurations. By reducing the effective angle of attack of the vortical flow, peak buffeting responses were shifted to higher angles of attack.

Active control of wing rock using tangential leading-edge blowing

Experiments were performed to demonstrate positive poststall roll control of a free-to-roll wind-tunnel delta wing model using tangential leading-edge blowing. Previous static experiments had shown that significant rolling moments could be produced up to an angle of attack of 55 deg using asymmetric tangential leading-edge blowing. The implication was that poststall dynamic roll control ought to be possible using only blowing. To demonstrate experimentally that this was indeed the case, a free-to-roll wind-tunnel model sting mounting system and a pair of fast acting blowing control servo-valves were developed and manufactured. An automatic feedback roll control algorithm using tangential leading-edge blowing was then synthesized and implemented on a digital controller. Results from the present dynamic experiments indicated that with just symmetric blowing alone, wing rock at an angle of attack of 55 deg was damped. Furthermore, with the use of an automatic roll feedback control algorithm employing asymmetric blowing, the same wing rock was stopped in less than one cycle of the limitcycle oscillation.

Roll moment characteristics of asymmetric tangential leading-edge blowing on a delta wing

The concept of asymmetric tangential leading-edge blowing (TLEB) for the control of separated vortical flows is presented. Experimental results for the development of roll moment on a delta wing at high angles of attack and sideslip have been obtained and the underlying flow mechanisms examined. The application of the concept as an aircraft control system is discussed.

Vortex control technique for the attenuation of fin buffet

The application of tangential leading edge blowing (TLEB) to reduce levels of single-fin buffeting has been studied. The tests were performed at the University of Bath 2.1 x 1.5 m wind tunnel, using two cropped 60deg delta wings. To measure the unsteady pressures on the fin surface, a rigid fin instrumented with miniature differential pressure transducers was used. A flexible fin of similar planform and size was used to measure the buffeting response. Steady-state static pressure data and laser light sheet flow visualization were employed to aid interpretation of the vortical flow over the wings, and hence, identify the causes of the buffeting. The profiles of the unsteady pressures and the buffeting response were found to match each other very closely. It was observed that symmetric leading-edge blowing modified the leading-edge vortices by reducing the effective angle of attack of the vortex. Blowing at a constant rate shifted the buffet excitation and response to higher angles of attack. Flow visualization confirmed that the mechanism at peak buffeting had not changed, but had been merely shifted. It has been shown that the use of an optimum blowing profile could completely suppress the buffeting response without impairing the wing lift characteristics.

Computational study of blowing on delta wings at high alpha

In this study, the flowfield produced by tangential leading-edge blowing on a rounded leading-edge 60-deg delta wing at high angle of attack is investigated computationally by solving the thin-layer Navier-Stokes equations. Steady-state flowHelds are calculated for various angles of attack, with and without the presence of tangential leading-edge blowing. The numerical grid is generated using algebraic grid generation and various interpolation and blending techniques. The jet emanates from a slot with linearly varying thickness, and is introduced into the flowfield using the concept of an actuator plane, thereby not requiring resolution of the jet slot geometry. The Baldwin-Lomax algebraic turbulence model is used to provide turbulent closure. The computational results are compared with those of experiments. The effectiveness of blowing as a rolling moment control mechanism to extend the envelope of controllabili ty is illustrated at different angles of attack. The saturation effect of increased blowing is captured well in the computations. Control reversal noted in similar experimental studies is also observed in the computations.

The Suppression of Single-Fin Buffeting Using Tangential Leading Edge Blowing on a Delta Wing

The application of tangential leading edge blowing to reduce levels of single-fin buffeting has been studied. The tests were performed at the University of Bath in the 2.1 m × 1.5 m wind tunnel using two cropped 60° delta wings. To measure the buffet excitation, a rigid fin instrumented with miniature differential pressure transducers was used. A flexible fin of similar planform and size was used to measure the buffeting response. Steady state static pressure data and laser light sheet flow visualization were employed to aid interpretation of the vortical flow over the wings, and hence identify the causes of the buffeting. The profiles of the buffet excitation and response were found to match each other very closely. It was observed that the leading edge blowing modified the leading edge vortices by reducing the ‘effective angle of attack’ of the vortex. Blowing at a constant rate shifted the buffet excitation and response to higher angles of attack. Flow visualization confirmed that the mechanism at peak buffeting had not changed, but had been merely shifted. It has been shown that the use of an optimum blowing programme could completely suppress the buffeting response.

Control of asymmetric vortical flows over delta wings at high anglesof attack

Results from a wind tunnel experiment will be used to confirm that Tangential Leading Edge Blowing is capable of controlling the vortical flow over a delta wing to very high angles of attack. The production of significant rolling moments and the ability to unburst a vortex has been demonstrated to 55 angle of attack. Strain gauge balance measurements and upper surface pressure distributions will be presented which illustrate the various modes of operation and which, in particular, identify the uncoupled/coupled nature of the vortex control at pre- and post-stall angles of attack. At angles of attack beyond 40°, rolling moments are produced that exceed those produced by 20 of aileron deflection at 0 angle of attack.

Control of vortical lift on delta wings by tangential leading-edge blowing

An experiment has been performed to examine the feasibility of vortex control by tangential mass injection at the leading edge of a 60 deg delta wing. The initial results indicate that direct control of the primary separation allows significant control of the vortex flow up to angles of attack of 60 deg. At lower angles of attack, the vortical flow may be removed entirely from the surface of the wing, recovering the fully attached flow case. The effects of the mass injection have been shown to be decoupled from the geometric angle of attack, allowing the possibility for controlling lift without changing attitude. Nomenclature b =wing semispan c =wing root chord Cg' = spanwise sectional rolling moment coefficient CL' = wing rolling moment coefficient Cn = spanwise sectional normal force coefficient CN = wing normal force coefficient Cp = pressure coefficient CM = bio wing momentum coefficient CM * = crossflow blowing momentum coefficient h = slot height Vj =jet velocity Fw = freestream velocity ae = effective angle of attack oig = geometric angle of attack e = wing semi apex angle