Airfoil Pressure Distribution Research Articles

High Lift Characteristics of an Airfoil Placed in a Narrow Channel

Aerodynamic characteristics of an airfoil moving in a narrow channel bounded by two parallel walls, i.e. ground and ceiling, are studied theoretically and experimentally. Lift acting on an airfoil at a positive attack angle increases as the airfoil approaches either ground orceiling. This study deals with the combination of ground and ceiling effects to realize a high lift wing. A theory is presented for the calculation of two-dimensional inviscid flow around an arbitrary airfoil placed in a narrow channel, using singularity method in which proper circulation is distributed directly on the airfoil contours. Sample calculation shows the influences of ground and ceiling on the lift and moment coefficients of the airfoil. Two-dimensional experiment is conducted to measure the pressure distribution of airfoil, from which lift and pressure drag coefficients are evaluated. Theoretical and experimental results are compared and the characteristics of this kind of high lift wings are discussed.

Airfoil in a Contracting or Diverging Stream

A theoretical and experimental investigation of the flow around an airfoil in a contracting or diverging stream is carried out in this paper. An expression for the vortex distribution, which satisfies the kinematic condition on the airfoil surface and the Kutta condition at the trailing edge, is derived. The predicted values of the lift and the surface pressure distribution, at various values of incidences and mean flow acceleration, agrees very well with the measured values. In converging flow, the circulation and lift are found to increase with increase in velocity ratio (ratio of outlet to inlet velocity). Considerable change in airfoil pressure distribution is observed, its effect being dominant on the suction surface. With diverging mean flow, both circulation and lift decrease with decrease in velocity ratio. The decrease in mean velocity seems to have dominant effect on the pressure surface. Finally, the theoretical and experimental investigation seems to indicate that the ratio of lift coefficients, with and without change in mean flow, can be expressed as CL/CL2d = VR, where VR = velocity ratio.

Methodology for Structural Optimization of STOL Aircraft Vertical Stabilizers

In a converging flow, the circulation and lift increases with increase in velocity ratio (outlet velocity/inlet velocity). There is also considerable change in airfoil pressure distribution, its effect being dominant on the suction surface. In a diverging flow, both the circulation and lift decrease with decrease in velocity ratio. The effect of change in mean velocity on pressure distribution is likely to be dominant on the pressure surface. These changes in the airfoil pressure distribution affect the viscid characteristics of the airfoil, thus adversely affecting the cavitation characteristics of a hydrofoil or pump blade, stall characteristics of a wing, pressure rise characteristics of a fan or compressor blade row. Incorporation of these effects is, thus, a practical necessity. The pressure distribution measured at midspan and at Z = 3 in. are found to be identical, thus confirming the validity of the quasi two-dimensional approach taken in this paper. The theory is valid exactly at the midspan of the airfoil, where the span wise velocity is zero, and becomes progressively inaccurate near the converging or diverging walls, where the spanwise velocities cannot be neglected.

Airfoils in Two-Dimensional Nommiformly Sheared Slipstreams

Abstract : A theoretical and experimental program was conducted to investigate the aerodynamics of an airfoil in a two-dimensional nonuniformly sheared slipstream. A mathematical model was developed to predict airfoil pressure distributions in such a slipstream and was used successfully for slipstreams with moderate shear. Pressure distributions over a wide angle of attack range were measured experimentally on an airfoil at each of seven different locations in a highly sheared two-dimensional slipstream. Study of the pressure distributions obtained on the airfoil at a location slightly above the flow centerline and also at a location slightly below the flow centerline indicates that the large effects on stalling characteristics are due to differences in the upper surface pressure distributions. These pressure distributions are affected by the freestream shear. Moreover, in the data obtained for airfoils located near the flow centerline, the differences in the lift appear to be caused primarily by differences in the stagnation pressure of the streamline which intersects the airfoil. This stagnation pressure is a function not only of airfoil location relative to the slipstream, but also of the angle of attack of the airfoil. (Author)

Airfoil pressure distributions in low-speed stall.

Airfoil pressure distributions in low-speed stall.