Objective
The primary objective of the present research program is the improvement of the performance of transonic transport aircraft by applying shock boundary layer interaction control. This means specifically to minimize the drag due to the presence of a shock, to prevent shock-induced separation and to alleviate or postpone the occurrence of buffet.
A thorough investigation of passive shock boundary layer interaction control was performed with the following results:
- The basic experiments have identified the mechanism of control and shown that due to control the single shock is replaced either by a theta-shock or an almost continuous (isentropic) pressure rise which results in a substantial reduction in wave drag; however, the combined blowing - suction (secondary flow) effect and the hole roughness cause an increase in viscous drag which, in determining total drag, will oppose the reduction in wave drag. Furthermore, new control laws have been derived and general deficiencies pointed out.
- Computer codes were successfully extended to treat airfoil flow with control. Corresponding computations predicted for the laminar-type airfoils a considerable reduction in wave drag but also an increase in total drag due to control. The computed boundary layer data clearly showed an increase in momentum thickness over the control region, amplified by the adverse pressure gradients over the rear part of the airfoils, generating viscous drag which overcompensates the reduction in wave drag. The unsteady computations showed a strong damping of the shock oscillations.
- The airfoil tests showed for the laminar airfoils a reduction in wave drag and an increase in total drag in agreement with the computations and for the reasons outlined above. For the turbulent airfoil a marginal reduction in total drag was achieved possibly due to the presence of a thicker boundary layer which seems to be less susceptible to the disturbances in the control region. The results also indicated an improvement of the buffet boundary due to control.
Concerning drag it may now be concluded that passive control can be ruled out as an effective means of reducing drag of laminar wings; even for a turbulent wing, the sensitivity of the effectiveness of passive control to changes in flow parameters makes this control device impracticable, especially since benefits in drag reduction are rather marginal. Nevertheless, there may be applications where drag reduction is not the main driver and passive control may still be of use, for instance, for supersonic intakes, where the objective is to avoid shock induced separation, and, of course, for transonic aircraft where the performance is limited by buffet considerations rather than drag. Finally, since passive control does not seem a viable method for reducing drag, other active or hybrid control techniques must be considered.
In order to achieve this we must:
- improve our knowledge of the physics of the control mechanisms and establish physical models and realistic boundary conditions,
- study relevant influence parameters (eg shock strength, hole inclination, etc).
- extend prediction methods to account for SBLIC employing these physical models and boundary conditions,
- carry out tests on realistic (airfoil) configurations up to flight Reynolds numbers to validate these computational methods and
- assess the efficiency of the SBLIC concept by experiment and computation.
In this way, we will provide the tools needed to design wings with SBLIC and, at the same time, demonstrate its potential in improving wing design and off-design performance. Note that the present effort will initially concentrate on the investigation of passive control which seems to provide the best overall efficiency since no additional power input is required.
Fields of science (EuroSciVoc)
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
CORDIS classifies projects with EuroSciVoc, a multilingual taxonomy of fields of science, through a semi-automatic process based on NLP techniques. See: The European Science Vocabulary.
- engineering and technology mechanical engineering vehicle engineering aerospace engineering aircraft
- natural sciences computer and information sciences computational science
- social sciences law
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Coordinator
37073 GOETTINGEN
Germany
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