As an important device of power generation systems, the radial-inflow turbine is usually employed in the small-scale distributed power generation system with renewable energy (e.g. wind and solar energy). The radial-inflow turbine shows several advantages compared to the axial-inflow turbine, such as high efficiency with small mass flow rate, compact structure and high reliability, etc. The overall system efficiency has been affected greatly by the turbine performance, and a detailed internal flow analysis is usually performed to identify and quantify the distribution of loss in the aerodynamic optimization process. According to the first and second law of thermodynamics, perhaps the most common definitions of loss are the total pressure loss and entropy generation, respectively. However, there are further problems with these loss definitions in practical experiments. The total pressure loss coefficient is not directly applicable in a rotating blade row. The relative total pressure or relative total enthalpy could change as a result of changes in radius rather than the dissipation of stagnation parameters. The entropy generation could not be measured directly in experiments. Since the flow is from the radial direction to axial direction, both the experimental measurements and loss analyses are much more difficult in radial turbines. Limited open literature to date has reported the loss measurement or analysis in the radial-inflow turbine. Further research should be undertaken to investigate the physical mechanism of loss in the internal flow field.

Inspired by the synergetic relation among physical quantities in the convective heat transfer, the synergy principles between the velocity and velocity gradient might provide new insights into loss analyses. To establish general synergy relations in the radial-inflow turbine, a curvilinear coordinate in a rotating frame is used, and three synergy relations are revealed by mathematical expressions in the streamwise, spanwise and circumferential direction, respectively. Based on the numerical results in a typical radial turbine, the relationship between the synergy principles and losses are discussed in detail. The understanding gained shows that the synergy principle between the velocity and velocity gradient represents the flow resistance in the internal flow field. The synergy angle might provide a new way to demonstrate losses in the radial-inflow turbine. The high-loss regions agree well with the regions where the synergy angle is less than about 72°. The synergy principle of the streamwise direction could represent losses on the blade-to-blade surface, and the losses on the theta-span surface could be indicated by the synergy principle of the spanwise or circumferential direction. Besides, the synergy angle shows similar results in both the stator and rotor, suggesting the synergy principle is applicable in both stationary and rotating blade row. The results of the volume-averaged synergy angle show that the enhancement of flow resistance is mainly in the rotor passage, especially under the variable rotating speed conditions. Both the local and volume-averaged value of synergy angle could express the variation of flow resistance under off-designed conditions. The present work may provide new perspectives into the physical understanding of the flow and loss, and a practical guidance on the aerodynamic optimization of the radial-inflow turbine.


Physical Quantity Synergy in the Internal Flow Field and Application in Radial-Inflow Turbines

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

Turbo Expo - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.