Studies On Aerodynamic Performance Of Helium Circulator Diffuser

With the steady growth of China’s energy demand as well as the increasingly serious environmental problems such as PM2.5 and carbon emission,nuclear energy are getting more and more attention as a kind of efficient and clean energy source.And nuclear energy will be an important choice to replace traditional fossil fuels and achieve the target of energy conservation and emission reduction.The high-temperature gas-cooled reactor-pebble bed module(HTR-PM) designed by Tsinghua University has the characteristic of high thermal efficiency and inherent safety,and HTR-PM is one of the safest reactor models. As the only active equipment in the primary coolant circuit, the helium circulator drives the coolant helium to circulate in primary circuit and exchange heat with reactor core.So the helium circulator plays an important role for the economy and safety of HTR-PM. However,there is a lack of research on aerodynamic performance of the helium circulator especially on the diffuser optimization and the unsteady pressuredue to rotor-stator interaction between impellers and diffusers so far.As the main aerodynamic part of the helium circulator,both steady and unsteady performance of the diffusers will be investigated in this paper.Investigations are performed to study the geometry optimization of the heliumcirculator with different vaneinlet angle.The corresponding external characteristics and flow field will be compared to determine the optimization scheme of the diffuseradjusted to the impeller in the helium circulator.And more detailed flow mechanism willalso be obtained in this paper. Research in this paper shows that:(1) The best vane inlet angle for the helium circulator in this paper is 16 deg, which can make the helium circulator meet the static pressure rise requirement of 200 kPa at any flow rate and obtain high isentropic efficiency;(2) The optimum vane inlet angle range by static pressure rise or isentropic efficiency at the same flow rate is in agreement;(3) Too low or too high vane inlet angle may cause the generation of vortex with wide range or low velocity area with large pitchwise rangeinside the vane passage, which makes helium decelerate and diffuse worse and finally results in the decrease of static pressure rise and isentropic efficiency of the helium circulator.Pressure at every monitor point inside the helium circulator flow passage at different instants will be obtained by unsteady flow calculation at design flow rate. Then the Fast Fourier Transformation method will be used to investigate the pressure fluctuation of these monitor points to get the change rule of main frequency and amplitude of pressure fluctuation along radial and pitchwise direction.Research in this paper shows that:(1) The main frequency and amplitudeof pressure fluctuation inside the impeller passage include the frequency that is1 to 4 times as well as 17 times the rotational frequency, and the frequencyequal to3 times the rotational frequency corresponds to the highest amplitude inside the impller passage.(2) The main frequency and amplitude of pressure fluctuation inside the vane passage include the frequency that is 2, 3, 4, 6 and 17 times the rotational frequency, and the frequencyequal to 3 times the rotational frequency corresponds to the highest amplitude inside the vane passage.