Power generation with a supercritical CO2 closed regenerative Brayton cycle has been successfully demonstrated using a bench scale test facility. A set of a centrifugal compressor and a radial inflow turbine of finger top size is driven by a synchronous motor/generator controlled using a high-speed inverter. A 110 W power generating operation is achieved under the operational condition of rotational speed of 1.15kHz, CO2 flow rate of 1.1 kg/s, and respective thermodynamic states (7.5 MPa, 304.6 K) at compressor and (10.6 MPa, 533 K) at turbine inlet. Compressor work reduction owing to real gas effect is experimentally examined. Compressor to turbine work ratio in supercritical liquid like state is measured to be 28% relative to the case of ideal gas. Major loss of power output is identified as rotor windage. It is found the isentropic efficiency depends little on compressibility coefficient. Off design performance of gas turbine working in supercritical state is well predicted by a Meanline program. The CFD analysis on compressor internal flow indicates that the presence of backward flow around the tip region might create a locally depressurized region leading eventually to the onset of flow instability.
The effect of circumferential single grooved casing treatment on the stability enhancement of NASA Rotor 37 has been examined with computational fluid dynamics analysis. Stall inception mechanism of Rotor 37 is presented first with principal focus on the tip leakage flow behavior, passage blockage, and the vortical flow structures. Detailed observation showed that the combined interaction of the stagnated flow of tip leakage vortex breakdown and the jetlike leakage flow from the midchord region leads to the blade tip-initiated stall inception. The result of numerical parametric study is then demonstrated to show the effect of varying the axial location and the depth of a circumferential single groove. The evaluation based on stall margin improvement showed a higher potential of deeper grooves in stability enhancement, and the optimal position for the groove to be located was indicated to exist near the leading edge of the blade.
The effect of circumferential single grooved casing treatment on the stability enhancement of NASA Rotor 37 has been examined with CFD analysis. Stall inception mechanism of Rotor 37 is presented first with principal focus on the tip leakage flow behavior, passage blockage, and the vortical flow structures. Detailed observation showed that the combined interaction of the stagnated flow of tip leakage vortex breakdown and the jet-like leakage flow from the mid-chord region leads to the blade tip-initiated stall inception. The result of numerical parametric study is then demonstrated to show the effect of varying the axial location and the depth of a circumferential single groove. The evaluation based on stall margin improvement showed a higher potential of deeper grooves in stability enhancement, and the optimal position for the groove to be located was indicated to exist near the leading edge of the blade.
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