Sidewall Boundary-layer Effects Research Articles

Effect of sidewall boundary layer on transonic flow over a wing

an upstream modification. The reflections ensure that a subtle modification has an affect over a large portion of the plume. Therefore, when effecting thrust vectoring in this manner, a designer needs to make full use of wave reflections to achieve the design goal. This study has certainly suggested areas for further investigation. First, there is the optimization issue. No attempt was made to find the optimum contour necessary to produce a required thrust vector angle. Obviously, the most efficient implementation of this technique would insure the largest thrust vector angle for the smallest wall contour modification. A study needs to be conducted into optimizing nozzle contours, initially for specified force angles, and then subsequently for entire force angle envelopes. A second area where further investigation is needed is based on the fact that only a two-dimensional analysis was performed. A three-dimensional study must be performed to identify any side wall affects on pitch vectoring. Also, yaw vectoring could be accomplished in a very similar manner by flexing the side walls. A very high performance nozzle with both pitch and yaw vectoring could possibly be designed.

Effect of sidewall suction on flow in two-dimensional wind tunnels

A closed-form analysis of flow in a two-dimensional subsonic wind tunnel that uses sidewall suction around the model to reduce sidewall boundary-layer effects is presented. The model problem that is treated involves a flat plate airfoil in a tunnel with a suction window shaped to permit an analytic solution. This solution shows that the lift coefficient depends explicitly on the porosity parameter of the suction window and implicitly on the suction pressure differential. For a given sidewall displacement thickness, the lift coefficient increases as the suction-window porosity decreases.

Simulations of reflected-shock waves in shock tubes taking account of side-wall boundary-layer effects.

Numerical simulations are conducted for behaviors of reflected-shock waves interacting with side-wall boundary-layers in shock tubes. A finite-difference procedure is developed as a solver of the thin-layer Navier-Stokes equations. This procedure, which combines the Lax-Wendroff-FCT scheme with the Crank-Nicolson scheme, is applied to initial and boundary conditions in which effects of shock-tube side-wall boundary-layers. are taken account of by use of the Pohlhausen polynomials. Computations are carried out for reflected-shock waves in nitrogen and in argon gas, respectively. Bifurcated reflected-shock waves, observed experimentally in polyatomic gases in shock tubes, are reproduced in simulations for nitrogen gas and compared with semiempirical theory for bifurcated reflected-shock waves. Good agreements between them lead us to conclude that the present procedure can simulate essential parts of interactions between reflected-shock waves and side-wall boundary-layers.

Effect of sidewall boundary layer on a wing in a wind tunnel

Three-dimensional viscous flow calculations are performed for a swept NACA 0012 wing mounted inside a wind tunnel for which detailed experimental data are available. A Runge-Kutta time-stepping scheme is used for obtaining steady-state solutions to the thin-layer Navier-Stokes equations. The effect of the wind-tunnel sidewall boundary layer on the flow pattern over the wing surface, particularly in the vicinity of the wing/wall juncture, is found to be significant. The computed results agree well with the data over a major portion of the wing. The extent of flow separation is underpredicted on the wing, which is attributed to the use of an equilibrium turbulence model.

Effects of aspect ratio and sidewall boundary-layer in airfoil testing

A correction to account for the sidewall boundary-layer effects in two-dimensional airfoil testing is presented by taking into consideration the nonlinear variation of the crossflow velocity across the width of the tunnel. The crossflow effects in the wind tunnel are represented in an empirical manner by considering the inviscid, compressible flow between a straight and a wavy wall. The analysis shows significant reduction in sidewall boundary-layer effects on airfoil midspan measurements with increasing aspect ratio of the model. Application of the correction to wind-tunnel data on airfoils demonstrated the method to be satisfactory in correlating shock location and also in giving good agreement between the measured pressure distribution and computed free air predictions. shed due to loss of lift in the boundary layer and a consequent change in the effective angle of incidence. The second approach, proposed independently by Barn well2 and Winter and Smith,3 assumes the changes in the boundary-layer thickness due to model-induced pressure field to have a significant effect on the flow over the airfoil. Using the small disturbance equation and accounting for the changes in the width of the flow passage, Barnwell presented a simplified correction for the measured forces in the form of a modified Prandtl-Glauret rule to account for the attached sidewall boundary-layer effects. Barn well's correction gave good agreement with the experiments of Bernard-Guell e4 at low Mach numbers. Sewall5 extended Barn well's approach to transonic speeds using the von Karman similarity parameter. Recently, an alternative simpler form of the correction encompassing both the Barnwell and Sewall methods has been proposed by Murthy.6 The Barnwell-Sewall correction appears to be effective in giving a satisfactory comparison between the measured and calculated pressure distributions on several airfoils tested in the NASA Langley 0.3-m Transonic Cryo- genic Tunnel.79 These studies suggest that the change in the sidewall boundary-layer thickness due to the airfoil pressure field can be a significant source of blockage correction, particularly at transonic speeds. The Barnwell-Sewall correction has been derived under certain assumptions of simplified boundary-layer treatment and linear variation of the crossflow velocity across the width of the tunnel. These assumptions imply that the airfoil chord is sufficiently large so that the effect of the sidewall boundary layers can be considered to be quasi-one-dimensional. Barn- well10 has shown recently that the linear crossflow assumption is justified provided (4d*/b)(b/c)2 is small. Hence, this assumption is likely to become less accurate when the width of the tunnel is much larger than the airfoil chord (i.e., for high- aspect-ratio models).

Similarity rule for sidewall boundary-layer effects in airfoil testing

The simplified form of the similarity rule for sidewall boundary layer effects presented envisions the generation of changes in both airfoil thickness and freestream Mach number by the sidewall boundary layer. Within the small-disturbance approximation, this approach encompasses the methods of both Barnwell (1980) and Sewall (1982), and can accordingly be applied at speeds ranging from the lowest to transonic Mach numbers.

Effects of Sidewall Boundary Layers in Two-Dimensional Subsonic and Transonic Wind Tunnels

A transonic similarity rule which accounts for the effects of attached sidewall boundary layers in two-dimensional wind tunnels is presented along with results of an experimental investigation of sidewall boundary-layer effects. The rule appears valid provided the sidewall boundary layer both remains attached in the vicinity of the model and occupies a small enough fraction of the tunnel width to avoid substantial three-dimensional interaction with the model.

Nonstationary Oblique Shock-Wave Reflections: Actual Isopycnics and Numerical Experiments

Oblique shock-wave reflections in nitrogen for perfect and imperfect gases were investigated interferometrically in a 10x 18-cm shock tube. Comparisons are made with numerical experiments conducted by two different groups on regular and single-Mach reflections. Even though the analyses are for inviscid flows, the sidewall boundary-layer effects in the experiments are negligible, and the features of the calculated and actual inviscid flows are compared readily. It is found that the available numerical techniques will have to be modified or new approaches developed before acceptable agreement can be obtained between actual and numerical experiments. The very accurate interferometric data will provide a basis for comparison with future numerical methods, which also should include the two remaining cases of complexand double-Mach reflections as a test of their accuracy and applicability.

Experimental study of the impingement of a liquid jet on the surface of a heavier liquid

This study is concerned with the phenomenon of a liquid jet impinging normally on the surface of a heavier immiscible liquid. In essence, the work is a continuation of a previous investigation which involved an air jet impinging on a water surface.An analytical model is presented which relates the velocity of the jet in the neighbourhood of the interface to the depth of cavity created by the jet. The effect of interfacial tension is taken into account. Numerous experiments were conducted utilizing both circular and plane jets. An oil jet impinging on water and a water jet impinging on carbon tetrachloride were studied. The resulting experimental data were analysed in terms of the dimensionless quantities obtained from the analytical model.Results obtained from the circular-jet experiments were in close agreement with the results of the previously conducted air-water tests. However, there were some discrepancies in the plane-jet results; side-wall boundary-layer effects may be the explanation. Depending on the relative values of the Froude and Weber numbers, interfacial tension may be important in determining the depth of cavity created by a jet. Finally two intriguing phenomena, viz. interfacial shearing and cavity oscillation, were observed in the plane-jet experiments.