An Experimental And CFD Research On The Low Pressure Exhaust Hood Of A Stream Turbine

The low pressure exhaust hood plays an important role in the stream turbine. The stream discharged from the last stage blade is collected by the exhaust hood and guided into the condenser. During this process the speed of the stream slows down with the pressure rising up, and the substantive leaving kinetic energy is recovered. The diffusion capability of the exhaust hood represents the ability of leaving kinetic energy recovery. As the same vacuum degree of the condenser throat, the higher pressure diffusion capability would result in the lower pressure at the outlet of the last stage. And there will be more enthalpy that can be used by the stream turbine. But another point is as the kinetic energy is recovered, there will be some energy loss due to the complicated vortex transport. So the performance of a steam turbine exhaust hood can be evaluated by the diffusion capability and the energy loss.It will make sense for the energy conservation that do research on the flow flied character of the exhaust hood and find out how to improve its performance by means of good understanding of the flow flied to increase the efficiency.The subject investigated was a reduced-scale model of an ultra supercritical steam turbine. The flow field character and performance was investigated through the experiment and the numerical simulation. For the experiment, first the flow flied of the exhaust hood was measured with a hot-wire anemometry under the condition of uniform inflow, and the inlet velocity distribution was acquired. Then the pressure distribution on the flow guide and the bearing cone was measured with a pressure scanivalve. And the flow field character on some special circumferential planes and the outlet plane was investigated with a particle image velocimetry (PIV). Combining with the passage flow velocity distribution which was measured by the hot-wire anemometry, the loss mechanism was analyzed. For the numerical simulation, the rationality and accuracy were verified through the comparison between the experimental data and the simulation results. And then the further study of the flow flied and performance of the exhaust hood model were carried out by means of numerical simulation. It was discovered that arranging baffle in the lower part of the exhaust hood could break the passage vortex that occupied the main flow area may improve the performance. And as a result an experimental advice on the method of arranging baffle was put forward.