AbstractSince the first flight of the Wright brothers, there has been considerable effort devoted to improving wing performance. Many techniques have been developed to reduce drag and improve the lift of aerofoil. This research introduces a new novel method, a so called "air bearing device" (ABD) which provides both drag reduction and enhancement of lift.
The basic principle of this technique is to introduce a groove in the solid upper surface and an air stream is injected into one side of the groove and then removed from the other side. The direction of this secondary flow is essentially parallel to the main flow and all the injected fluid is completely removed from the suction side. This flow is thus similar to an "air roller". The benefits of the device depend on the injection velocity and the geometry of the ABD groove. Optimizing the shape of the ABD constitutes a wide area for future research. The performance of the ABD was studied both theoretically and experimentally.
This device is considered to enhance the main flow in two ways. Firstly it appears to 'energize' the main flow by injecting some kinetic energy to the "weak" fluid particles near the wall. Secondly the pressure drop associated with the high speed of the flow inside the ABD is assumed to 'absorb' some of the adverse pressure resistance. The boundary layer thickness of the main flow is then reduced and, consequently, the main flow will be more capable of resisting separation. The source of the injected/sucked flow inside the ABD may be an external supply (an auxiliary fan) or may be taken from the higher/lower pressure regions around the aerofoil. One of the main objectives of the present study is to investigate theoretically the design aspects and the parameters that affect the ABD performance. The other objective is to investigate experimentally the effect of the device. Due to limitations in the experimental facility, it was not possible to examine experimentally all the theoretical cases. It should be noted however that optimization of the performance of the ABD was not the intention in this study.
The results obtained from this investigation were extremely promising and it can be concluded that:
The geometry of the ABD can effect the performance and will need to be optimized in future work.
• When the “rolling" velocity in the ABD exceeds the main stream flow speed, improvements in lift and drag are obtained.
• The improvements in drag and lift greatly exceed the penalty of the power consumption needed to operate the ABD.
• The increase in lift and decrease in drag occur simultaneously and up to 30% improvements were achieved.
Optimization of the performance of the ABD is a very wide area of research due to large number of parameters and strong interactions existing between them. Since the concept of the ABD is new the project was aimed at clarifying the general behavior of the device at this stage.
|Date of Award||Jul 1997|
|Supervisor||Talal Maksoud (Supervisor) & John Ward (Supervisor)|