Numerical investigation about backflow of film cooling in static turbine blade leading edge

Chao Gao,Huimin Zhou,Yiwen Ma,Haiwang Li,Ruquan You

doi:10.1177/1687814019885817

Abstract

In this article, film cooling characteristics, especially the phenomenon of backflow for the straight turbine blade leading edge, are investigated. Shear stress transport k-ω turbulence model and structured grids are employed to assure the accuracy of the simulation, and the computational method is verified by the available experimental data. The influences of blow ratio, hole diameter, and the spacing between holes in each row are analyzed. The formation mechanism of backflow is discussed to prevent it from happening or relieve the degree of backflow, thereby to improve the cooling efficiency. The results showed that backflow can be avoided by adjusting the structure and the layout of film cooling holes. With increase in blow ratio, the cooling film becomes more obvious at first and then fades gradually for departing from the blade surface. The jet flow is influenced by the total pressure ratio between coolant cavity and surface of blade leading edge. Smaller film hole diameter and larger hole spacing makes it easier to eject coolant and form continuous film by slowing down the pressure in the cavity. Increasing ratio of hole spacing to hole diameter ( p/ d) can effectively prevent backflow, whereas larger p/ d also makes the film coverage area smaller.

Highlights

Modern advanced gas turbines operate in temperature over the melting point of the blade to satisfy the needs of higher thermal efficiency and specific power output, which promotes the development of cooling techniques
The influencing factors of the film cooling performance mainly include the geometric parameters of the film holes and aerodynamic parameters, such as blow ratio, density ratio, mainstream velocity, and rotation speed
With the increase in the effective blow ratio, the film can be off the blade surface, so there can be a value to allow coolant eject from all three rows of holes and this specific blow ratio varies with the change of hole diameter

Summary

Introduction

Modern advanced gas turbines operate in temperature over the melting point of the blade to satisfy the needs of higher thermal efficiency and specific power output, which promotes the development of cooling techniques. Considering that there are 93 to 183 film cooling holes distributed at different positions on the leading edge of the blade with different local blow ratios, Figure 2.

Results

Conclusion