Boundary Layer Mass Flow Research Articles

Numerical investigation of impact of fixed-exit boundary-layer bleed on supersonic intake performance

Results of numerical investigation of flow and performance characteristics of a rectangular supersonic intake with boundary-layer bleed system are presented. The effects of several flush slot bleed geometric parameters including entrance and exit area, plenum size, rear edge vertical displacement and the position relative to the incident shock have been studied to clarify their effects on the compression performance. The viscous flowfield has been obtained by solving Favre averaged Navier-Stokes equations with shear stress transport (SST) k-ω turbulence model. Moreover, the numerical methodology deployed is validated with the experimental data from literature. The analysis has been carried out in the freestream Mach number range of 1.8-2.5 and at 00 angle-of-attack, corresponding to a unit Reynolds number of approximately 1.9−2.7×107 m−1. The results show that with the use of bleed, the exit flowfield uniformity as well as the critical and peak total pressure recovery (TPR) improves considerably at all operating conditions. Furthermore, the analysis indicates that the exit throat area of a slot bleed operating at a particular design condition can be increased up to a point such that it is just sufficient to eliminate the upstream boundary-layer at its peak operation. The variation in the bleed entrance area or its position relative to the throat entrance only alters the critical performance depending on the supercritical boundary-layer mass flow loss; however, the peak TPR or the sustainable backpressure remains the same at all upstream conditions, controlled by the fixed-exit throat area. Further, it is found that for the removal of comparable amount of boundary-layer mass flow, the effects of pure flush slot or of a configuration with slight vertical displacement at its rear edge, located at the same position are similar.

Experimental and Computational Investigations of a Normal-Hole-Bled Supersonic Boundary Layer

A series of experiments have been conducted on a bleed hole array spanning the width of the Cambridge University Engineering Department supersonic wind tunnel at Mach numbers of 1.8 and 2.5. The wind tunnel was run with varying levels of suction, and the flow structure over the bleed array was subsequently mapped with a laser Doppler velocimetry system at a resolution of 0.25 hole diameters or better. The same wind-tunnel setup was simulated using the OVERFLOW Navier–Stokes equation solver. The information obtained was used primarily in qualitative comparisons of flow patterns. Overall good agreement was found in the definition of the expansion fan and barrier shock pattern produced by flow entering the normal holes, as well as three-dimensional flow patterns. Both studies agreed well in terms of measured mass flow rates, to within 1% of the boundary-layer mass flow. The presence of the barrier shock standing off the downstream edge of the bleed holes corresponded with a jet of upward flow, which may provide a mechanism for the generation of streamwise vortices.

Similarity solutions for MHD thermosolutal Marangoni convection over a flat surface in the presence of heat generation or absorption effects

The problem of steady, laminar, thermosolutal Marangoni convection flow of an electrically-conducting fluid along a vertical permeable surface in the presence of a magnetic field, heat generation or absorption and a first-order chemical reaction effects is studied numerically. The general governing partial differential equations are converted into a set of self-similar equations using unique similarity transformations. Numerical solution of the similarity equations is performed using an implicit, iterative, tri-diagonal finite-difference method. Comparisons with previously published work is performed and the results are found to be in excellent agreement. Approximate analytical results for the temperature and concentration profiles as well as the local Nusselt and sherwood numbers are obtained for the conditions of small and large Prandtl and Schmidt numbers are obtained and favorably compared with the numerical solutions. The effects of Hartmann number, heat generation or absorption coefficient, the suction or injection parameter, the thermo-solutal surface tension ratio and the chemical reaction coefficient on the velocity, temperature and concentration profiles as well as quantitites related to the wall velocity, boundary-layer mass flow rate and the Nusselt and Sherwood numbers are presented in graphical and tabular form and discussed. It is found that a first-order chemical reaction increases all of the wall velocity, Nusselt and Sherwood numbers while it decreases the mass flow rate in the boundary layer. Also, as the thermo-solutal surface tension ratio is increased, all of the wall velocity, boundary-layer mass flow rate and the Nusselt and Sherwood numbers are predicted to increase. However, the exact opposite behavior is predicted as the magnetic field strength is increased.

The entrainment flow adjacent to an isothermal vertical surface

Results of numerical calculations of the buoyancy-induced flow adjacent to a vertical isothermal surface with a leading edge are presented. Coordinate transformations have been used to allow efficient calculation of both the boundary layer flow and the extensive ambient entrainment in-flow. A motion pressure field, which develops owing to the motion pressure deficit at the surface, drives this entrainment. Increased boundary layer mass flow results, compared with classical boundary layer theory. Conduction into the upstream entrainment region is appreciable, ahead of the leading edge. This flow, below the surface, arises as a mass sink for the distant entraining flow. Motion pressure effects determine the flow in this leading edge entrainment region and in the entrainment flow arising along such a heated surface. Modeling of both these regions is of increasing importance in many technologically important applications, such as electronics packaging.

Transition effects on airfoil dynamics and the implications for subscale tests

p Re 5 t At U x z a a. ot0 A e 6 A v £ p \l/ co, co Nomenclature disturbance amplitude disturbance amplitude in freestream initial disturbance amplitude in boundary layer reference initial disturbance amplitude in boundary layer at Mr(= 1.3) airfoil chord mean aerodynamic chord drag, coefficient CD = D/(p00Ux>/2)S frequency proportionality constant, Eq. (1) lift, coefficient CL = L /(p^ Ul/2)S sectional lift, coefficient cl = l/(p00(/i/2)c Mach number mass flow injected calculated mass flow in boundary layer just upstream of air holes sectional pitching moment, coefficient cm-mp/

Surface wing predictions and boundary layer mass flow : Joffre, S.M., 1983. Geophysica, 20(1):51–69

Surface wing predictions and boundary layer mass flow : Joffre, S.M., 1983. Geophysica, 20(1):51–69

Flowfield Analysis for Successive Oblique Shock Wave-Turbulent Boundary-Layer Interactions

A computation procedure is described for predicting the flowfields which develop when successive interactions between oblique shock waves and a turbulent boundary layer occur. Such interactions may occur, for example, in engine inlets for supersonic aircraft. Computations are carried out for axisymmetric internal flows at M 3.82 and 2.82. The effect of boundary layer bleed is considered for the M 2.82 flow. A control volume analysis is used to predict changes in the flow field across the interactions. Two bleed flow models have been considered. A turbulent boundary layer program is used to compute changes in the boundary layer between the interactions. The results given are for flows with two shock wave interactions and for bleed at the second interaction site. In principle the method described may be extended to account for additional interactions. The predicted results are compared with measured results and are shown to be in good agreement when the bleed flow rate is low (on the order of 3% of the boundary layer mass flow), or when there is no bleed. As the bleed flow rate is increased, differences between the predicted and measured results become larger. Shortcomings of the bleed flow models at higher bleed flow rates are discussed.

Experiments on control of supersonic transitional flow separation using distributed suction.

An experimental program was conducted to determine the effectiveness of distributed boundary-layer suction for controlling transitional flow separation at supersonic speeds. Testing covered Mach numbers of 2.5, 3.0, and 3.5 and a Reynolds number range (based on flare axial location) from 0.8 X 10 6 to 6.4 X 106. The tests were made on a slotted, 20-caliber, tangent-ogive cylinder-flare model having flare angles of 7.5° and 15°. This experimental research demonstrated that distributed suction was an effective means of reducing the extensive areas of transitional-type flow separation that developed on an adiabatic wall, bodyof-revolution flare model at relatively low Reynolds numbers. The reduction in flow separation for a particular flare angle was found to correlate as a function of the percent of the boundary-layer mass flow removed. The separated flow region was very responsive to distributed suction with a suction mass flow of approximately 10% of the total undisturbed mass flow in the boundary layer at the flare leading edge station being required to eliminate separation upstream of the 15° flare.

Total boundary-layer mass flow with mass transfer at the wall.

Total boundary-layer mass flow with mass transfer at the wall.