The emission footprint of the aviation sector can be decreased by reducing the structural weight of airplanes. Nowadays, airplanes are able to withstand dynamic peak loads, caused e.g. by gust or manoeuvres, by employing sturdy and hence heavy structures. Active load alleviation can contribute to reduce the airplane’s structural weight by mitigating the peak aerodynamic loads. The focus of this work is on load changes induced by gusts, which are dimensioning for the airplane’s structure and less predictable than manoeuvre load changes. Conventional surfaces, as ailerons, trailing edge flaps and spoilers, offer partial load alleviation, because of their inertia-limited achievable deflection angles. In order to obtain a more complete gust load alleviation, novel active flow control systems are investigated as they could offer the required control authority with reaction time adequate to compensate all gusts defined by certification documentation. Furthermore, the fast reaction time can be crucial to offer enough time for the gust load alleviation control system to react. Load changes induced by 1 - cos type gusts are evaluated with 2D- Unsteady Reynolds Averaged Navier–Stokes (URANS) simulations at different altitudes, flow conditions and gust-lengths. The gustinduced load changes are used as a lift reduction target for several potential actuator concepts, in order to identify the most promising ones. The load change capabilities of the actuators are evaluated with 2D-RANS at different operating conditions, focusing on the subsonic flight conditions. A trailing edge flap (flap), a jet blown perpendicularly to the airfoil’s upper surface (normal jet) and a jet blow tangentially over a convex surface integrated in the airfoil’s trailing edge area (circulation control actuator) offer control authority suitable for gust load alleviation. The reaction times of these three actuators are estimated with 2D-URANS simulations and compared with the load change evolution induced by the shortest gust defined by certification documentation at different altitudes and flight Mach numbers. The three actuators are activated impulsively and the power required by each of them is estimated. The circulation control actuator offers high and fast control authority suitable for mitigating gusts defined by certification documentation while featuring limited power requirements. 2D-circulation control airfoil is designed and experimentally tested at a moderately high Reynolds number Rec = 1.6 106 and low Mach number M = 0.14. The actuator features a dual slot layout system, which allows implementation of the jets on both airfoil sides and hence the ability to increase and decrease the airfoil’s lift. The two jets can be activated simultaneously and independently. The circulation control actuator shows high control authority with peak changes in lift coefficient of circa 0.36 and lift-to-equivalent-drag ratio changes up to 100. The simultaneous employment of upper and lower jets is found to produce higher lift-to-equivalent-drag ratio change than single upper or lower blowing, furthermore providing the possibility of partially decoupling lift and pitching moment changes. The reaction time of the actuator is a crucial aspect for gust load alleviation. Consequently, in order to test the reaction time of the circulation control airfoil, several impulsive switching between different initial and final blowing conditions of both upper and lower jets are tested. The actuator demonstrates a fast reaction time, reaching the steady value faster than the occurrence of the maximum load change induced by the shortest gust defined by certification documentation. The rate of change of the circulation control actuator is between 2-3 times faster than conventional surfaces implemented nowadays on airplanes. The frequency response behaviour of the actuator is further analyzed by testing periodic square wave activation signals. The tests are conducted at different steady operating conditions of the actuator and with different frequencies of the wave signal, allowing the identification of a dynamic model for the actuator. Furthermore, the actuator allows more complex activation profiles such as 1 - cos shapes which would offer a lift history suitable for alleviating 1 - cos gusts. Different 1 - cos like gust load changes are created in the wind tunnel with a pitching airfoil upstream of the circulation airfoil, inducing a maximum lift coefficient change of 0.2 with an onset time about two times shorter than for the shortest gust defined by certification documentation. The gust load alleviation performance are evaluated with a root mean square factor, and the circulation control airfoil is able to provide a load reduction up to 81%, with respect to the load induced by a predetermined upward gust. Furthermore, the actuator is integrated in a feedforward control strategy with a two component hotwire acting as a gust detector. The load alleviation capabilities are tested with different upward and downward gusts, at different steady operating conditions and controllers. Even with the small anticipation time offered by the hotwire, the actuator is able to provide up to 35% gust load alleviation. Overall, the circulation control actuator is a suitable actuator for gust load alleviation as it offers high control authority in the time frame of the shortest gusts defined by certification documentation.
Experimental and numerical investigation of gust load alleviation on subsonic wings
Experimentelle und numerische Untersuchung der Böenlastminderung an Unterschallflügeln
2025
Sonstige
Elektronische Ressource
Englisch
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