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Aerodynamics and Heat transfer computation in Turbo-machinery

Fig.1 Fluid Flow over a turbine blade

In most cases,the flow field across a turbine blade consists of three domains. These are the Laminar, the Transitional and the Turbulent region. Refer to Fig.1.

The Laminar flow can be solved on the basis of the Navier-Stokes equation.

The Transition zone is very hard to solve for but is usually solved via non-dimensionalizing and statistical models.

The Turbulent zone can be solved for with the help of boundary layer equations combined with the Navier-Stokes Equation.

The major problem is when one had to define the boundary conditions and formulate the closure equations. These are to, often solved numerically as they have a lot of boundary conditions, a lot of irregularities and are highly non-linear.

There are certain things which are hence essential to the prediction of the Aerodynamics fields and heat transfer losses. These include:

• Pressure Difference computations

• Prediction of the boundary layers and their growth

• Prediction of transition length and heat transfer

• Prediction of temperature gradients within the blade

The prediction methods take into account:

1. Heat flux models- To carry out the computation of viscous layer and heat transfer, there is a need to develop constitutive equations for the temperature and velocity correlations. These equations are developed under heat flux models
2. Governing equations and boundary conditions- A brief review of the computational efforts for heat transfer prediction is covered in this section. These efforts constitute the application of boundary conditions and the selection of appropriate governing equations.

Using these models we can then discuss Computation for uncooled/convectively cooled blades Computation for Film-blades