Design and Aerodynamic Performance of High Pressure Axial Flow Fan

D2 - Aerodynamic Design

Modern coal fired power stations fitted with desulphurization equipments require axial flow fans with high pressure coefficient and flow rate. The fans consist of one or two axial stages and inlet suction chamber and exhaust diffuser. A proposed paper will be devoted to design and experimental and theoretical investigations of aerodynamic performance of stage blading and complete fan for design rotor blades stagger angles. Flow simulations results were obtained by means of Numeca commercial code.
Fan stage with hub/tip ratio of 0,6 has design pressure and flow coefficients values: 0,83 and 0,60, respectively. A geometry of stage blade rows was determined by the application of a code for axial compressor stage design using streamline curvature method for axisymmetric flow solution. Rotor and stator blade elements have relatively high aerodynamic loading. It is expressed by diffusion factor originally devised by Lieblein. The maximum values of rotor and stator rows diffusion factor were 0,57 and 0,54.

Inlet chamber flow area has rectangular shape with sides ratio of 1,28. The inlet velocity vector is perpendicular to machine axis. Three variants of chamber struts were considered. Area ratio of exhaust diffuser is 1,87.

In the first step of aerodynamic research the fan stage was measured on test rig with external diameter of 600 mm. Obtained experimental aerodynamic performance proved that stage design targets were fulfilled. Maximum stage efficiency value was found :90,1% ±1.2%. Measured and computed aerodynamic performance curves were in acceptable agreement. The flow fields and energy losses were investigated in stage planes with the help of pressure 5 hole conical probes. The obtained experimental spanwise distributions of rotor and stator loss coefficients were compared with computed ones at design point.
Then the complete axial flow fan with stage diameter of 600 mm was investigated on test rig built up according to ISO standards. Theoretical relations derived on 1D flow analysis in complete fan showed that fan efficiency decreases with energy losses of inlet chamber and diffuser and with square of flow coefficient. This tendency is weakened by the increase of stage pressure coefficient. These conclusions were confirmed by experimental and flow simulation results. At design point the difference between experimental stage blading and fan efficiency values was 7- 8%.
Comparison of experimental and computed aerodynamic performance of complete axial flow fan showed good agreement at three typical working points. A basic variant of inlet chamber with seven struts was used in order to obtain good stiffness of bearing support. Struts in lower part of inlet chamber were longer and thicker than in the upper part. An analysis of flow mechanism in inlet chamber and diffuser was carried out on the basis of flow simulation data. Energy losses of these fan parts did not significantly change with volume flow rate variation. The flow simulation results obtained in axial flow fan with 3 variants of inlet chamber have shown that the decrease of number, length and thickness of struts increases fan efficiency value.