Turbine Blade Cooling CFD Simulation
The present problem simulates the cooling of turbine blades.
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Introduction to turbines and their cooling
Since the turbine produces work by converting thermal heat energy into mechanical energy, increasing the temperature and initial pressure of the fluid increases the heat energy of the fluid, thereby increasing the rate of conversion of thermal energy into mechanical energy and ultimately increasing work production. Therefore, one of the most important issues related to turbines is to study the cooling systems of turbine blades to increase the efficiency of turbine operation, reduce the thermal stresses caused by high temperatures on the surface of the blades and finally increase the blades lifetime.
One of the most common methods of cooling in turbines is to use hollow blades, it means to make the inside of the blades empty in order to flow the coolant or airflow. This cooling process takes place through internal cavities in various ways such as convection, spraying, layering, and perforation. The figure below shows a view of the turbine blade with a special cooling-working hole.
The present problem simulates the cooling of turbine blades. To simplify the problem model, considering the symmetrical structure of the turbine body and its blades, only one blade is simulated. The main purpose of the problem is to investigate the temperature distribution and changes in thermal energy on the body and turbine blade; therefore, the process of simulating the model and defining the boundary conditions of the model performed in such a way that the fluid behavior focused on heat transfer. The cooling process in this model is based on the definition of cool airflow in an empty space in the inner walls of the blade.
These inner walls have a series of holes to increase the contact surface with the cold flow and thus increase the cooling process. Therefore, the boundary condition of heat transfer has been used on the surfaces of the outer and inner walls of the blade, so that the outer surface of the blade and its lower body, which are under the hot working airflow of the system, have a transfer coefficient of 200 watts per cubic meter and the temperature of 1672 Kelvin and the inner surface of the blade, which is cooled by the cold airflow, has a heat transfer coefficient of 200 watts per cubic meter under a cold flow of 300 Kelvin.
Turbine Blade Geometry & Mesh
The present 3-D model is drawn using the CATIA software and then imported into the Design Modeler software. The geometric structure of the model consists of a piece of a turbine blade, which includes the body of the turbine blade with a certain angle of curvature and cross-section of the airfoil, the inner wall with space and certain pores, and the central base body under the blade. In fact, to simplify the problem, due to the symmetry of the blades, only modeling has been done for one blade. The figure below shows a view of the geometry.
The meshing of the present model has been done using ANSYS Meshing software. The mesh type is unstructured and the element number is equal to 10154723. The size of the grids in the areas adjacent to the inner cavities of the fins is smaller and more accurate. The following figure shows the mesh.
To simulate the present model, several assumptions are considered, which are:
- A Pressure-Based solver has been performed.
- Simulation has been performed in both fluid and thermal states (heat transfer).
- The simulation is steady.
- The effect of gravity on the fluid is not considered.
The following is a summary of the steps for defining a problem and its solution:
|Boundary conditions (turbine blade cooling)|
|Wall||Root’s wall and Outer wall|
|200 W.m-2.K-1||heat transfer coefficient|
|1672 K||free stream temperature|
|200 W.m-2.K-1||heat transfer coefficient|
|300 K||free stream temperature|
|Solution Methods (turbine blade cooling)|
|second order||pressure||Spatial discretization|
|second order upwind||momentum|
|second order upwind||energy|
|Initialization (turbine blade cooling)|
After the solution process is complete, 2-D and 3-D temperature contours are obtained in the space between the outer wall of the blade (in contact with the hot flow) and the inner wall of the blade (in contact with the cooling flow). Also, the amount of heat transfer coefficient is obtained on the inner and outer walls of the blade and the blade base. The two-dimensional contours in the XZ section are drawn at different distances of 0.004, 0.016, 0.028 and 0.04 meters from the upper surface of the blade base, as well as in the XY section at different distances.
All files, including Geometry, Mesh, Case & Data, are available in Simulation File. By the way, Training File presents how to solve the problem and extract all desired results.