Boundary Layer Separation Region Research Articles

衝撃波の入射位置が壁面燃料噴射場における燃焼と流れ場に及ぼす影響

Experimental and numerical studies of the interaction between combustion of a hydrogen jet and an incident shock wave were performed. In the case that an incident shock wave was introduced upstream of the injection slot, the boundary-layer separation region was extensively expanded. The penetration height of the Mach disk with an incident shock wave was less than that without an incident shock wave. Combustion was confirmed when the incident shock wave was introduced downstream of the fuel injection slot, while, with the incident shock wave upstream of fuel injection slot, combustion was not confirmed. The mechanism of these phenomena was discussed based on the results of numerical simulation in terms of the residence time in the separation region near the fuel injection slot.

Turbulent Flow Simulations Using the Maccormack and the Jameson and Mavriplis Algorithms Coupled with the Cebeci and Smith and the Baldwin and Lomax Models in Three-Dimensions

In the present work, the MacCormack scheme and the Jameson and Mavriplis scheme are implemented with the Cebeci and Smith model and the Baldwin and Lomax model to perform turbulent flow simulations in a threedimensional space. The Navier-Stokes equations in conservative and integral forms are solved, employing a finite volume formulation and a structured spatial discretization. The MacCormack scheme is a predictor/corrector method which performs coupled time and space discretizations, while the Jameson and Mavriplis algorithm is a symmetrical scheme and its time discretization is performed by a Runge-Kutta method. Both schemes are second order accurate in space and time and require artificial dissipation to guarantee stability. The steady state problem of the supersonic turbulent flow along a ramp is studied. The results have demonstrated that both models predict satisfactorily the boundary layer separation region formed at the compression corner, reducing, however, its extension in relation to the laminar solution, as expected.

Study on shock wave and turbulent boundary layer interactions in a square duct at Mach 2 and 4

In this paper, the outline of the Mach 4 supersonic wind tunnel for the investigation of the supersonic internal flows in ducts was firstly described. Secondly, the location, structure and characteristics of the Mach 2 and Mach 4 pseudo-shock waves in a square duct were investigated by color schlieren photographs and duct wall pressure fluctuation measurements. Finally, the wall shear stress distributions on the side, top and bottom walls of the square duct with the Mach 4 pseudo-shock wave were investigated qualitatively by the shear stress-sensitive liquid crystal visualization method. The side wall boundary layer separation region under the first shock is narrow near the top wall, while the side wall boundary layer separation region under the first shock is very wide near the bottom wall.

A hybrid high accuracy difference scheme and its applications

In this paper a hybrid high accuracy difference scheme has been proposed. The new scheme is a combination of a third-order accuracy scheme given in [3,4] with the ENN scheme proposed in [1]. Numerical tests showed that the new scheme has higher accuracy than the ENN scheme in the smooth regions and boundary-layer separation regions.

Gas bubbles bursting at a free surface

When a small air bubble bursts from an equilibrium position at an air/water interface, a complex motion ensues resulting in the production of a high-speed liquid jet. This free-surface motion following the burst is modelled numerically using a boundary integral method. Jet formation and liquid entrainment rates from jet breakup into drops are calculated and compared with existing experimental evidence. In order to investigate viscous effects, a boundary layer is included in the calculations by employing a time-stepping technique which allows the boundary mesh to remain orthogonal to the surface. This allows an approximation of the vorticity development in the region of boundary-layer separation during jet formation. Calculated values of pressure and energy dissipation rates in the fluid indicate a violent motion, particularly for smaller bubbles. This has important implications for the biological industry where animal cells in bioreactors have been found to be killed by the presence of small bubbles.

Turbulent separated flow over and downstream of a two-element airfoil

Flow characteristics in the vicinity of the flap of a single-slotted airfoil are presented and analysed. The flow remained attached over the model surfaces except in the vicinity of the flap trailing edge where a small region of boundary-layer separation extended over the aft 7% of flap chord. The airfoil configuration was tested at a Mach number of 0.09 and a chord Reynolds number of 1.8 × 106 in the NASA Ames Research Center 7- by 10-Foot Wind Tunnel. The flow was complicated by the presence of a strong, initially inviscid, jet, emanating from the slot between airfoil and flap, and a gradual merging of the main airfoil wake and flap suction-side boundary layer.

Turbulent separated flow over and downstream of a two-element airfoil

Flow characteristics in the vicinity of the flap of a single-slotted airfoil are presented and analysed. The flow remained attached over the model surfaces except in the vicinity of the flap trailing edge where a small region of boundary-layer separation extended over the aft 7% of flap chord. The airfoil configuration was tested at a Mach number of 0.09 and a chord Reynolds number of 1.8 × 106 in the NASA Ames Research Center 7- by 10-Foot Wind Tunnel. The flow was complicated by the presence of a strong, initially inviscid, jet, emanating from the slot between airfoil and flap, and a gradual merging of the main airfoil wake and flap suction-side boundary layer.

Analysis of wings with flow separation

An interactive viscous/inviscid procedure has been developed combining a three-dimensional panel method with an inverse finite-difference boundary-layer method. The scheme incorporates both a two-dimensional and a quasi-three-dimensional boundary-layer scheme. The resulting method has been applied to the calculation of the flow over three-dimensional wings and wing/body configurations and it has been shown that the procedure can compute flows with significant regions of boundary-layer separation.

Interaction of a blown gas jet with a supersonic oncoming stream without formation of a three-dimensional region of boundary layer separation

A study is made of the flow resulting from the interaction of a supersonic stream with a transverse sonic or supersonic jet blown at right angles to the direction of the main stream through a nozzle whose exit section is situated on a flat wall.

Effect of flow split on separation and stagnation in a model vascular bifurcation.

This is a study of the flow disturbance in a plastic model of an asymmetric vascular bifurcation. A sidearm was attached to the mainlimb at an angle of 15 degrees to the inlet flow axis. Water at steady flow was used and flow patterns were demonstrated by a dye injection technique. The proportion of inlet flow (Qi) exiting from the sidearm (Qs) was varied and flow patterns were recorded photographically. A laser Doppler anemometer (LDA) was used to measure near-wall velocity. At a physiologic Reynolds' number of 500, no flow disturbance occurred in the mainlimb when the sidearm was completely occluded. When the fraction of flow exiting from the sidearm (Qs/Qi) reached 0.19, a region of boundary layer separation developed along the wall of the mainlimb opposite the flow divider. This region of nearly static fluid spread circumferentially around the mainlimb as Qs/Qi increased. Near-wall velocity within the separation decreased and became negative when Qs/Qi = 0.31. When Qs/Qi reached 0.38, the separation enveloped the wall of the entire bifurcation with a shell of slowly moving fluid. At the same time, the rapidly moving mainstream impinged directly on the flow divider. There is a similarity between the region of separation seen in this model and the site of formation of atherosclerotic plaque at the carotid bifurcation. Separation may contribute to atherogenesis by creating a region of low wall shear at bifurcations.

Effects of Boundary Layer Turbulence Promoters on the Local Film Coefficients of ML-1 Fuel Elements

Local convective heat transfer coefficients for a surface with integral boundary-layer turbulence promoters were determined by conducting naphthalene-to-air mass transfer tests and invoking the heat transfer-mass transfer analogy. The turbulence promoters were machined into the convex surface of an annulus. The experimental results were normalized relative to mass transfer coefficients on a smooth surface with parallel flow.On the faces of the turbulence promoters local heat transfer coefficients up to six times the smooth surface value were encountered. High transfer coefficients were found on the upstream and top faces. Coefficient values on the downstream surfaces were low and independent of geometry. Corner areas showed heat transfer coefficients lower than those for a smooth surface with parallel flow.The data from surfaces between two turbulence promoters were correlated in terms of a dimensionless location index. A broad heat transfer coefficient peak of 2.4 times the smooth surface magnitude was found 4 turbulence promoter heights downstream from a promoter. Each test also showed a narrow coefficient peak at the point about 0.5 height preceding a turbulence promoter. When correlated in this manner, the results revealed a unique generalized distribution of the transfer coefficient for surfaces with boundary layer turbulence promoters of rectangular cross section. The upstream and downstream regions of boundary layer separation were independent of the dimensions of the turbulence promoters.The estimated error for this series of tests was approximately ±20 % of the maximum relative transfer coefficient values.