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Zaqie March 29, 2010 14:01

Water turbine - TSR/power
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I am working on a turbine problem.

I have been trying to get the power extracted by the turbine. Initially I had meshed in ICEM CFD with tetra/prism meshing. I ran the simulation in Fluent.

My settings are as follows

Solver Pressure based, velocity formulation absolute, steady
Viscous SST k-omega turbulence model
Moving reference frame The turbine is to rotate in clockwise direction as viewed from inlet about x axis, hence given a negative rotational velocity in the cell zone condition(as viewed from the moving reference frame)
Boundary conditions Inlet – inflow velocity (constant along positive x axis), reference - absolute
Outlet – pressure outlet with a gage pressure of 1 atm (2 atm absolute pressure) , I had used massflow outlet before
Symmetry – outer cylindrical domain
Periodic - rotational
Turbine- Wall…moving relative to adjacent cell…zero velocity
Solution Method Coupled second order
Solution Initialization From Inlet…Relative to cell zone
Convergence criteria 10e(-06)

Think everything that I have set up is right.

The basic problem I am facing is I tried to calculate the power. From forces>moments I get the torque and that multiplied by rotational velocity and 3 times(for three blades) I get the power.

As seen in experimental results I should get a curve of Cp as shown in the figure(increasing first and then decreasing after a peak). Instead I get Cp which is ever increasing with increasing TSR(tip speed ratio = (rotational velocity* radius)/stream velocity)), even going above 1(ideally should not go above 0.6).

I have increased the TSR by fixing the inflow velocity and changing the rotational velocity.

Now, I have tried blocking using ICEM and run the simulations in the same fashion(because I thought the mesh is an issue). I still get the same results.

Would like to know why these erratic results are coming up. Somebody please help.

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