Cooling and Heat Transfer in Gas Turbine Systems

As thermodynamic cycle analysis shows, gas turbine efficiency increases with an increase in turbine inlet temperature. However, maximum achievable turbine inlet temperature is bounded by the maximum temperature which the blade material can withstand. Various cooling measures are therefore employed to alleviate heat loads on the turbine blades. Film cooling acts by supplying compressor bleed air onto the surface of the blade through the film holes drilled in the surface (Figure 1). Some of the major difficulties in developing film cooling strategy is the sensitivity of the problem to the details of geometrical and physical conditions, and complex flow dynamics.

We developed an integrated compressible - low Mach number solver allowing to couple instantaneous dynamics of the flow in the plenum, film hole and above the blade surface in a situation where flow regimes range from supersonic (external flow) to almost stagnating (plenum, M~10^-4) [1]. With the developed solver, we performed LES simulations of film cooling flow issued from an array of inclined cylindrical holes into a flat plate turbulent boundary layer [2, 3]. Collaboration with Dr. David Bogard of UT Austin allowed us to perform detailed comparison between simxulation results and experimental data. Geometrical setup of experiments of Bogard et al. [4] as well as our computational setup are shown in Figure 2.

Figure 1. Rolls-Royce plc, "The Jet Engine"
Renault Printing Birmingham 1996

a) Experimental setup (Bogard et al. [4])

b) Computational setup (Peet & Lele [2, 3]).
Green - plenum; blue - film hole; red - external flow region.

Figure 2. Problem setup

Accurate modeling of all pertinent geometry components combined with an accurate desciption of the turbulence field (LES method) allowed us to obtain good agreement with experiments. Complex interaction between the plenum, jet and crossflow defines the near-field dynamics of the flow, and influences the far-field properties. For the current configuration, the in-hole separation and jetting effect are observed due to the sharp turn from the plenum into the film hole (Figure 3). As a result, the velocity distribution at the film hole exit (velocity minimum at the center) is far from the fully-developed turbulent pipe flow (velocity maximum at the center).

a) Plenum-jet-crossflow interaction

b) Inside the film hole

Figure 3. Mean velocity magnitude and streamlines

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References