Operating point of turbine

The Operating point of a turbine, is defined by the rotational speed and the fluid velocity. The propeller turbine must have an optimized twist to its operating point. The optimization of the propeller turbine through the analysis of its performance at different operating points.

For a propeller turbine, converting the energy of a fluid stream in torque on a shaft, the actual speed, of the energy capture propeller, will be the speed that balance:

• The motor torque generated by the propeller during passage of fluid into its blades,
• and the resistive torque produced by the generator, which is connected the propeller.

For a propeller propellant type, engine torque is the engine of the aircraft or vessel, and the rotation speed is stabilized when the resistant torque of the propeller is equal to the engine torque. The approach is similar to a propeller designed for energy capture or propulsion, we must find a balance point between the motor torque and the load torque.. This is the point of intersection of the torque curve the propeller and the curves of the motor or generator, depending on the rotational speed. o quickly see what will be the operating speed of your system: generator / turbine or motor / propeller, Simply place on a same graph, the torque curve of the propeller, and the torque curve given for the motor or generator.To facilitate graphics resolution, of the actual operating point of the system, it is possible to insert your torque curve (provided by the manufacturer of the generator or motor) and make it appear superimposed:

input torque curve:

It is possible to enter multiple torque curves representing several motors or generators (3 motors curves in the example below) and editing performance curves, depending on the rotational speed, to view directly the speed of rotation and the performance of the same propeller mounted on a variety of motors or generators of different powers:

So here we find that:

• the propeller mounted on the engine whose torque is described by curve 1 operate at 1300 rpm
• the propeller mounted on the engine whose torque is described by curve 1 operate at 1750 rpm
• the propeller mounted on the engine whose torque is described by curve 1 operate at 2400 rpm

We can also overlay performance data and thrust to know the performance of the system in all three cases:

ISo here we find that:

• the propeller mounted on the engine, whose torque is described by the curve 1, will provide a thrust of 150 newton at 1300 rpm and a shaft power of about 300 watts
• the propeller mounted on the engine, whose torque is described by the curve 2, will provide a thrust of 250 newton at 1750 rpm and a shaft power of about 1200 watts
• the propeller mounted on the engine, whose torque is described by the curve 3, will provide a thrust of 550 newton at 2400 rpm and a shaft power of about 3400 watts

Of course these values ​​are valid only if the propeller has a strength appropriate to the calculated thrust, and that cavitation does not spray fluid. We must therefore control these parameters, at speeds of rotations found!