Design And Improvement Of A 70MW Radial Turbine Within A Closed Supercritical CO₂ Brayton Cycle

Impeller machinery has always been one of the most important components in the field of energy conversion.It uses a variety of fluid media as the working medium,and uses the energy stored in the working medium to promote its work to achieve the purpose of energy conversion.With the increasingly serious energy shortage problem and the proposal of environmentally friendly new energy,the current society pays more and more attention to high-performance power cycle.The closed Brayton cycle power system using carbon dioxide as the circulating working fluid has received more and more attention.In this paper,a 70 MW supercritical carbon dioxide radial turbine is designed and optimized.The effects of the number of impeller blades,tip clearance,blade hub fillet radius and blade inlet and outlet angle on the aerodynamic performance of the radial turbine are studied by numerical simulation.First,the impeller blade shape is optimized.The results show that the optimal blade inlet angle of the blade needs to meet zero attack angle or a small negative attack angle,and the optimal blade outlet angle should take the maximum value when the geometric limit is met.The result provi des experience for the design of impeller in the future.Secondly,by studying the effect of blade tip clearance on turbine aerodynamic performance,it was found that the existence of blade tip clearance caused leakage flow.The more the leakage flow,the larger the vortex size caused by the interaction between the leakage flow and the cross flow fluid,the more obvious the effect on the mainstream,and the increased flow loss.Therefore,the tip clearance of the supercritical carbon dioxide radial turbine should be the minimum value allowed by the processing accuracy.Furthermore,by studying turbines with different blade numbers,it is found that too few blades cannot effectively control the fluid to complete the flow direction change in the impeller,which will lead to an increment in flow loss in the mainstream area and a decrease in efficiency.Under different working conditions,the five numbers of blade radial turbines can all achieve the highest efficiency points at 90%,100%,110%,and 120% speeds.For turbines with the same number of blades,as the speed increases,the pressure ratio corresponding to the highest efficiency point is higher.Finally,through the study of different blade hub fillet radius of turbine,we founded that when the blade hub fillet radius is too small.Due to the corner zone effect,a large area of low velocity fliud area occupying 80% of the cross section will be formed near the blade hub.If the hub fillet radius is too large,the flow area will be reduced,and a vortex will be formed near the trailing edge.At the same time,the area of the low-speed area will gradually expand and the flow loss will increase again.Therefore,there is an optimal value for the blade hub fillet radius.The selection of the value of the blade hub fillet radius in engineering application needs to satisfy both the safety factor and the aerodynamic factor.In order to ensure the stability of the variable operating condition and the economic performance of the radial turbine,specific conclusions should be drawn after comprehensive consideration.