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Engineering Edge

Turbine Vane Cooling with FloEFD

By Leonid Gurov, Dr. Svetlana Shtilkind, Dr. Gennady Dumnov, 
Mentor Graphics, 
Mechanical Analysis Division

Gas turbines play an important role in many applications, such as aero-engines, power generation and natural gas production. To increase the power output and thermal efficiency of gas turbines the inlet temperature of the gas entering the turbine has to be increased, which in turn means that the efficient cooling of the turbine’s blades and vanes is essential. To eliminate the possibility of premature failure, designers must predict the local values of heat transfer coefficient and metal temperature as accurately as possible. This is where the application of CFD techniques comes into play.

While the traditional CFD simulation approach often requires a lot of user intervention including manual mesh generation and adjustments to the turbulence model. FloEFD reduces any such intervention to minimum. The study of an internally cooled turbine vane, for example, is clear-cut in FloEFD, eliminating the need to manually perform adaptive meshing of hot gas and coolant domains or solid vanes. In this particular case of an internally cooled vane, NASA C3X linear cascade, a well-known benchmark test case, was used to verify some of the data.

The resulting hot air flow around the cascade was defined in with experimental data [1]. Upstream of the vane (turbine inlet), fixed values of total pressure (3.217 Bar) and temperature (783 K) were specified. To achieve a transonic flow regime (Mach=0.9) downstream of the vane, the respective value of static pressure at the computational exit was defined. The resulting flow field represented in terms of Mach number distribution is shown in Figure 1.

Figure 1. Mach number distribution at mid-span of the C3X vane

To simulate convective heat transfer from the vane, which is made of stainless steel, to the coolant flow, two approaches were considered: general and simplified. The general approach implies the simulation of the coolant flow in each channel “as it is” and so suggests the 3D problem statement. As a result, non-uniform heat transfer along the vane height due to the coolant flow being heated can be captured in the simulation (Figure 2).

Figure 2. Metal temperature distribution predicted by FloEFD

The simplified approach assumes that average values of heat transfer coefficient between coolant and walls in each cooling channel are known. In this case the coolant flows can be excluded from the simulation and replaced by the corresponding boundary conditions on the walls of each channel that include average values of heat transfer coefficient and coolant temperature. Although the problem statement is reduced to 2D, such an approach can be used to estimate thermal characteristics of the vane at its mid-span.

Figure 3 shows metal temperature and heat transfer coefficient distributions at the mid-span obtained using both approaches. FloEFD predictions are in a good agreement with the corresponding experimental measurements making this study an excellent demonstration of the use of FloEFD technology to calculate a problem that is known for its high sensibility to mesh quality, turbulence modeling approach and boundary layer treatment.

Figure 3. Predicted metal temperature and heat transfer coefficient values at the vane's mid-span

Reference:

  1. Hylton, L. D., Mihelc, M. S., Turner, E. R., Nealy, D. A., and York, R. E.,1983, “Analytical and experimental evaluation of the heat transfer distribution over the surface of turbine vanes,” NASA Paper No. CR-168015.
 
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