Flow Past Airfoils Research Articles

Computer simulation of shock wave boundary layer interaction

Development of a boundary layer correction for an analysis program previously used by Bauer et al. (1972) to study two-dimensional flow past transonic airfoils at off-design conditions where shocks which interact with the boundary layer appear. Using a method which combines conformal mapping with a finite-difference scheme due to Murman and Cole (1971), an analysis is made of the interaction between shock waves on a supercritical wing section and a turbulent boundary layer, assuming that the shocks are weak and that separation is insignificant. It is shown that relatively simple shock wave/boundary layer interactions of the kind envisioned in this study can be treated by determining the displacement thickness iteratively together with the flow and altering the profile accordingly. It is concluded that the proposed boundary layer correction appears to furnish an essential improvement in cases where both pronounced aft loading and a large enclosed supersonic region of flow are present.

Experimental Investigation of Incompressible Flow Past Airfoils with Oscillating Jet Flaps

Experimental Investigation of Incompressible Flow Past Airfoils with Oscillating Jet Flaps

Surface Dipole Strength for Flow Past Airfoils

A new correlation technique enables the determination of local acoustic source strength on the surface of flat plates and simple airfoil shapes. The method is based on Curle's equation for surface generated noise and involves cross correlation between local surface pressure and the farfield acoustic pressure. Flat plate airfoils of circular planform were positioned in a quiet open jet airflow. The distribution of dipole strength was obtained by moving the point of surface pressure measurement around on the surface. Distinctively different distributions were obtained for cases of vortex shedding (airfoil at zero angle of attack in core of jet), separated flow (airfoil at 16° angle of attack in core of jet), and incident turbulence (airfoil in turbulent mixing layer). The popular notion that noise comes dominantly from the edges of a plate was not strongly supported. In some cases, however, definite localized source regions were identified. The technique also enabled estimates of correlation area for the surface pressure pattern to be made. These were generally a small fraction of the plate area (1%–10%). [Facilities and support for this work were provided by the Trane Company Research Department, LaCrosse, Wisconsin.]

Unsteady incompressible fluid flow past a cascade of thin curved plates

A large number of papers have been devoted to the study of unsteady flow past airfoil cascades. The majority of authors solve the problem for slightly curved profiles oscillating at low angles of attack. Among other work, we note that of Sohngen [1] on the flow past a dense cascade of plates oscillating synchronously and in phase in a potential fluid flow at a high angle of attack. Samoilovich [2] studied the flow past a cascade of plates of arbitrary shape oscillating with an arbitrary phase shift between neighboring plates. He presents the solution for the case of variable circulation in the quasisteady formulation. Stepanov [3] studied the same question with a linear approach to the flow behind the cascade. Musatov [4] examined the problem of the flow past a cascade of plates oscillating with an arbitrary phase shift between neighboring plates in a fluid flow, again at a high angle of attack, and considered the variation of the relative position of the plates durilng the oscillation process. The present paper considers the flow of a perfect incompressible fluid past a cascade of thin curved oscillating plates with account for the relative displacements of the plates during oscillation. To determine the intensity of the bound vortices per unit length, a linear integral equation is obtained. This represents a generalization of the Birnbaum equation to the case considered (see [5]). Equations are presented for calculating the unsteady aerodynamic forces and moments acting on the plates. As an example, the aerodynamic forces and moments are calculated for the quasistationary formulation of the problem.

An approximate solution for two-dimensional transonic flow past thin airfoils

AbstractThe transonic, two-dimensional flow past a thin airfoil is treated by approximating the transonic small perturbation equation by a linear equation valid in the neighbourhood of the airfoil. The solution is derived by representing the body by a line of suitable sources. Pressure distributions are given for airfoils with maximum thickness both forward and aft, and agreement with experiment improves as the position of maximum thickness moves aft.

The Characteristics of Roughness from Insects as Observed for Two-Dimensional, Incompressible Flow Past Airfoils

The Characteristics of Roughness from Insects as Observed for Two-Dimensional, Incompressible Flow Past Airfoils

Experimental Studies on the Stability of the Transonic Flow past Airfoils

Local flow fluctuations near the airfoil surface have been measured in the speed range near critical Mach number, by using a Mach-Zehnder interferometer and a rotating-drum camera. Airfoils tested are Tomotika-Tamada airfoil, NACA-0012 and 10 per cent thick elliptic cylinder. Experiments show that amplitude and frequency of oscillation that appears when the local sonic speed is exceeded on the surface depend on the shape of the profile. In the cases of T.T.- and 0012-airfoils, the oscillation is of small amplitude and high frequency when the maximum local Mach number on the surface is not much above unity, and the time-mean pressure distribution on the surface is smooth and shows no appreciable distortion due to shock waves. In the case of the elliptic cylinder, slow oscillation of large amplitude involving distinct shock waves appears, as soon as sonic speed is exceeded on the surface.