Effect of backward injection with combined hole on film colling performance

This study investigates the film cooling performance and flow features of backward injection with combined hole. This concept is evaluated by comparison to forward injection with combined hole and other forms with both injections, forward and backward. The shapes are namely, cylindrical hole, conical hole and fan-shaped hole. The eight configurations are computed for three blowing ratios M=0.5, 1.0 and 1.5. The air coolant was injected through holes inclined at 35° and 155° for forward and backward injection respectively. The lateral averaged film cooling effectiveness and the distribution of adiabatic film cooling efficiency are studied using commercial software ANSYS- CFX. In addition, several velocity vectors and contours are presented for analyzing the thermal behavior. The results show that a uniform coverage is obtained by the backward injection which leads to best cooling. The maximum improvement of film cooling is obtained by backward injection with combined hole at M=1.5.

Film Cooling in Rocket Nozzles

In this project supersonic, tangential film cooling in the expansion part of a nozzle with rocket-engine like hot gas conditions was investigated. Therefore, a parametric study in a conical nozzle was conducted revealing the most important influencing parameter on film cooling for the presented setup. Additionally, a new axisymmetric film cooling model and a method for calculating the cooling efficiency from experimental data was developed. These models lead to a satisfying correlation of the data. Furthermore, film cooling in a dual-bell nozzle performing in altitude mode was investigated. The aim of these experiments was to show the influence of different contour inflection geometries on the film cooling efficiency in the bell extension.

Large-Eddy Simulation of Film Cooling Performance Enhancement Using Vortex Generator and Semi-Sphere

Film cooling is an essential cooling method to prevent high-pressure turbine blade from melting down due to the high inlet temperature. In order to improve the film cooling efficiency, several flow control methods have been proposed. In this paper, large-eddy simulations are performed to study the effectiveness of a vortex generator (VG) and a semi-sphere installed downstream of the cooling jet. Before the detailed analyses, the numerical framework is validated against the available experimental data. Both the laminar and turbulent approaching boundary layers are considered. The turbulent boundary layer is generated by a numerical plasma actuator. After validation, the influence of VG and semi-sphere on the film cooling efficiency at various blowing ratios are analyzed. It is found that a counter-rotating vortex pair (CVP) is formed downstream and its strength increases with the blowing ratio in the configuration without VG/semi-sphere. When the VG is installed, it produces another vortex pair that rotates in the reverse direction of the CVP, which reduces the CVP strength and increases the lateral diffusion of the coolant. As a result, the film cooling efficiency is greatly improved, especially at a higher blowing ratio. For the case with a semi-sphere, the film cooling efficiency is also improved, especially at low–medium blowing ratios. However, it is not as effective as the VG in terms of enhancing cooling efficiency. In addition, the total pressure loss is calculated to examine the aerodynamic penalty associated with the VG and semi-sphere. It is found that the total pressure loss increased by only 1% due to the VG or semi-sphere, within the range of blowing ratio investigated in the current study. Considering the overall performance and the feasibility of being applied in practice, a semi-sphere installed downstream of the cooling hole is a promising method to improve the cooling efficiency.

Formation of film cooling on the turbine blade back and pressure side in the case of using V-shaped dimples

Alongside the development of methods of intensifying convective heat transfer inside the blade, development of methods of local improvement of the efficiency of film cooling of the blade’s surface is still of immediate interest. The film is formed on the blade surface in conditions of high-camber shape and low initial velocity of the gas flow in the vicinity of the leading edge with its subsequent abrupt acceleration. The paper presents some data on the peculiarities of film formation on the back and pressure side of the blade in the vicinity of the leading edge. Experimental temperature distribution over the adiabatic wall was obtained with the use of a FLIR-E 64501 thermal imager. It was found that the conditions for the film formation on the blade back are more favorable than those on the pressure side. It manifests itself in the fact that optimal blowing parameters on the blade back are considerably lower than those on the pressure side. The use of V-shaped dimples located on the wall immediately behind the holes for blowing was suggested as a measure for local improvement of film cooling efficiency. The efficiencies of film cooling in the formation of a curtain, without the use and with the use of V-shaped dimples behind the holes for blowing were compared. Local improvement of efficiency and uniformity of film cooling distribution with the use of V-shaped dimples behind the holes for blowing was observed.

FILM COOLING OVER A FLAT PLATE WITH COOLANT SUPPLY IN TO TRIANGULAR INDENTATION

The modern high-performance gas turbine engines operate at the flow temperatures exceeding the melting temperature of materials, which require the blade cooling. However, the traditional scheme of film cooling is characterized by appearance of secondary vortex structures that destroy the coolant film. From the existing alternative schemes of film cooling, which allow protecting the turbine blades from influence of high temperatures, the scheme with triangular dimples has demonstrated good results in the stationary conditions. This cooling scheme was patented and tested in the Institute of Engineering Thermophysics, National Academy of Sciences of Ukraine. In order to determine the feasibility of such a scheme, it is necessary to consider the effect of the blade rotation influencing the film cooling efficiency. The results are given towards theoretical investigation of the film cooling efficiency of this scheme under rotation conditions. The study was performed using the ANSYS CFX package using SST-turbulence model. The blowing ratio was varied from 0.5 to 2.0. Numerical simulation performed for rotation parameters corresponding to the dominant influence of the Coriolis force – 10, 100 rpm, and centrifugal forces – 3000, 5000 and 7000 rpm. Оn the basis of computer simulation, it has been shown that rotation does not affect weakly the average efficiency of film cooling at Coriolis force, but causes a peak displacement of local adiabatic efficiency, at rotation parameter of 7000 rpm, when there is a distortion of the flow lines.