Suction Angle Research Articles

Experimental Study of Heat Transfer Augmentation Near the Entrance to a Film Cooling Hole in a Turbine Blade Cooling Passage

Film cooling is extensively used by modern gas turbine blade designers as a means of limiting the blade temperature when exposed to extreme combustor outlet temperatures. The following paper describes an experimental study of heat transfer near the entrance to a film cooling hole in a turbine blade cooling passage. Steady state heat transfer results were acquired by using a transient measurement technique in a 40 times actual rectangular channel, representative of an internal cooling channel of a turbine blade. Platinum thin film gauges were used to measure the inner surface heat transfer augmentation as a result of thermal boundary layer renewal and impingement near the entrance of a film cooling hole. Measurements were taken at various suction ratios, extraction angles, and wall temperature ratios with a main duct Reynolds number of 25,000. A numerical technique based on the resolution of the unsteady conduction equation, using a Crank–Nicholson scheme, is used to obtain the surface heat flux from the measured surface temperature history. Computational fluid dynamics predictions were also made to provide better understanding of the near-hole flow. The results show extensive heat transfer enhancement as a function of extraction angle and suction ratio in the near-hole region and demonstrate good agreement with a corresponding study. Furthermore it was shown that the effect of a wall-to-coolant ratio is of a second order and can therefore be considered negligible compared with the primary variables such as the suction ratio and extraction angle.o

Numerical study of turbulent boundary layers with heat transfer and tangential transpiration

The hydrodynamic and thermal characteristics of the turbulent boundary layer developed on a porous wall with heat transfer and various angles of transpiration are analyzed numerically with the proper boundary conditions. The wall functions of the viscous and turbulent sub‐layers for velocity and temperature are modified to allow for the effect of the angle of injection and suction through the porous wall. The finite difference method based on a control volume approach is used for solving the time averaged Navier‐Stokes equations for incompressible flow in conjunction with the standard k‐ε turbulence model equations. A non‐uniform staggered grid arrangement is used. The parameters studied include the suction and injection velocity (Vw) and the angle (α) of the injection and suction. The present numerical results of the normal injection and suction are compared with a known experimental data and a good agreement is obtained. The numerical results also indicate that the characteristics of the turbulent boundary layer such as local friction coefficient and thermal boundary layer thickness are substantially influenced by the velocity and the angle of transpiration.

Numerical analysis of the effects of tangential transpiration on the boundary layer characteristics

In the present study, the characteristics of the turbulent boundary layer developing on a porous wall with various angles of injection and suction are analyzed numerically with the proper boundary conditions. The finite difference method based on a control volume approach is used for solving the time averaged Navier‐Stokes equations for incompressible flow in conjunction with the standard k‐ε turbulence model equations. The wall functions of the viscous and turbulent sub‐layers are modified to allow for the effect of the angle of injection and suction through the porous wall. A non‐uniform staggered grid arrangement is used. The parameters studied include the velocity (Vw) and the angle (α) of the injection and suction. The present numerical results of the normal injection and suction are compared with the known experimental data and a good agreement is obtained. The numerical results also indicate that the characteristics of the turbulent boundary layer such as local friction coefficient, boundary layer thickness and shape factor are substantially influenced by the velocity and the angle of injection and suction.

Suction effect on an impulsively started circular cylinder: Vortex structure and drag reduction

Drag reduction on an impulsively started circular cylinder by surface suction has been investigated with a joint numerical and experimental study. Two suction slots entraining mass with various rates were located symmetrically in a range of angles downstream of the points of zero shear stress. The Reynolds number Re of this study was between 500 and 2000, while the suction coefficient Ṁ varied from 0 to 0.08. Analysis based on the force contributed by fluid elements with nonvanishing vorticity [Chang, Proc. R. Soc. London Ser. A 437, 517 (1992)] has provided a clear view of the physical mechanism causing the drag reduction. For the impulsive flow with surface suction, the initial drag reduction is due to the strengthening of the front boundary layer, while the slender vortices in the near wake due to suction then become the dominant factor in reduction of the drag force in later stages. Close agreements were found between the experimental and numerical results, including streakline flow visualization and surface vorticity measurements on the top of the cylinder. In addition, a parametric study on the slot location, the suction angle, and the width of the suction slot has also been carried out in detail.

Similarity solutions for steady laminar convection along heated plates with variable oblique suction: Newtonian and Darcian fluid flow

The similarity solution ansatz that Burdé applied to adiabatic boundary-layer flow over flat plates and slender bodies of revolution is employed here to investigate mixed convection flow adjacent to heated inclined flat plates. Both Newtonian and Darcian fluids are considered under the assumption that they obey the Boussinesq approximation. New results fall into two distinct categories for heated plates with oblique wall suction. Class I problems correspond to radial source/sink flows interior to a wedge and class II problems pertain to uniform rectilinear flow over flat plates. Except in special cases, solutions of the class I equations must be obtained numerically while all class II equations possess explicit analytical solutions encompassing natural, mixed, or forced convection depending on the magnitude of the free-stream velocity. Numerical integration of prototype class I problems reveals single or dual solutions for radial outflow and an infinity of oscillatory solutions for radial outflow. The similarity solutions reported here describe flows with continuous distributions of temperature and suction angle along the plate, and in some cases the variation of the temperature, suction strength, or suction angle may be chosen freely.