In the framework of a joint project together with Hekyom (Fr), Aster designed and build a 6-rotor, 150mm diameter bi-directional turbine aimed to generate >10kW shaft power at 3000 rpm. Converting this shaft power into electricity is performed by standard 10kW brush-less electro-motor, used as generator having an mechanical to electric efficiency close to 90%. The layout of the turbine plus generator placed in a pressure vessel is shown here
Shown in detail below is the first guide vane with central bearing and the subsequent rotor-guide vane sets made using 3D printing.
Unfortunately the thermoacoustic engine to drive the turbine is not available yet. For that reason the turbine is preliminary tested and characterised at atmospheric pressure by measuring flow resistance and complex acoustic impedance at continuous and at alternating flow respectively. The measured impedance at the 130mm input tube as a function of rotational speed is shown below.
At low frequency and blocked rotor the absolute value of the impedance is complex induced flow resistance and acceleration of the gas between blades (inertance). At increasing rotational speed, the absolute values of the acoustic impedance rise and become more and more a real load to the acoustic source (output of the thermoacoustic engine)
The impedance is measured for the 6-rotor turbine but the effect of rotational speed on the impedance as described is typical for this type of bi-directional turbines.
As soon as the high power thermoacoustic source becomes available, tests with argon at elevated pressure will be performed. We expect the heavy gas (argon) at elevated mean pressure (3.5MPa) will improve acoustic to electric conversion efficiency up to 80%.