TY - CONF
T1 - The control of separation by periodic oscillations
AU - Wygnanski, I.
AU - Seifert, A.
N1 - Funding Information:
The airfoil experiments were performed in the Meadow-Knapp wind tunnel at Tel Aviv University. The project was sponsored in part by a grant from the Research and Development office of the Israel Ministry of Defense and monitored by Mr. A. Kuritzki. This is an assigned task on US/IS MOA on Rotor craft Aeromechanics. The Eppler airfoil was build by the AD&D company. The maperation with Dr. R. Yceli and Mr. A. Kariv from AD&D, Israel, was very helpful. The PR8-40 airfoil was designed and manufactured by IAI. Mr. Shepshelovits and MI. Koss from TASHN. IAI are acknowledged. This airfoil was modified to use oscillatory blowing by MI. M. Goldberg who also manufactured the oscillatory blowing valve. We also appreciate the permission granted by Dr. Mark Drela to use his ISES code at Tel Aviv University.
Publisher Copyright:
© 1994 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
PY - 1994
Y1 - 1994
N2 - It was recently demonstrated9,15 tbat oscillatory blowing is an effective method for delaying separation from a lifting surface, much more so than the steady blowing traditionally used for this purpose. Experiments carried out on different airfoils revealed that this flow depends on many parameters such as; the location of the blowing slot, the steady and oscillatory momentum coefficients of the jet, the frequency of imposed oscillations and the shape and incidence of the airfoil. In airfoils equipped with slotted flaps, the flow is also dependent on the geometry of the slot and on the Reynolds number in addition to the flap deflection which is considered as a part of the airfoil shape. The incremental improvements in a single element airfoil characteristics are generally insensitive to a change in Reynolds number provided the latter is sufficiently large. It became clear that an effective control of separation must be further subdivided into two distinct tasks: 1 Preventing of a complete detachment of the flow from the surface. 2 Forcing a separated flow to change its direction and reattach to the surface. Each of the above flow conditions should be treated differently because the problem as a whole is bi-stable over a wide range of flow parameters which lead to hysteresis. The investigation is being expanded to novel designs of very thick airfoils which are only efficient when integrated with the active separation control systems, and to compressible flow. These aspects of the program are also discussed.
AB - It was recently demonstrated9,15 tbat oscillatory blowing is an effective method for delaying separation from a lifting surface, much more so than the steady blowing traditionally used for this purpose. Experiments carried out on different airfoils revealed that this flow depends on many parameters such as; the location of the blowing slot, the steady and oscillatory momentum coefficients of the jet, the frequency of imposed oscillations and the shape and incidence of the airfoil. In airfoils equipped with slotted flaps, the flow is also dependent on the geometry of the slot and on the Reynolds number in addition to the flap deflection which is considered as a part of the airfoil shape. The incremental improvements in a single element airfoil characteristics are generally insensitive to a change in Reynolds number provided the latter is sufficiently large. It became clear that an effective control of separation must be further subdivided into two distinct tasks: 1 Preventing of a complete detachment of the flow from the surface. 2 Forcing a separated flow to change its direction and reattach to the surface. Each of the above flow conditions should be treated differently because the problem as a whole is bi-stable over a wide range of flow parameters which lead to hysteresis. The investigation is being expanded to novel designs of very thick airfoils which are only efficient when integrated with the active separation control systems, and to compressible flow. These aspects of the program are also discussed.
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U2 - 10.2514/6.1994-2608
DO - 10.2514/6.1994-2608
M3 - Paper
AN - SCOPUS:2142728137
T2 - AIAA 25th Plasmadynamics and Lasers Conference, 1994
Y2 - 20 June 1994 through 23 June 1994
ER -