Three dimensional numerical analysis of multi wing centrifugal fan

3-D numerical analysis of multi wing centrifugal fan-1 you bin e elhadi Xie Jun Long Wang Jun Wu Keqi (School of energy and power engineering, Huazhong University of science and technology, Wuhan 430074, Hubei Province) 3-D numerical analysis of the internal flow field of a forward curved multi wing centrifugal fan is carried out in this paper The results show that the Zui pressure in the volute is distributed in different circular positions along the axial direction There is an inlet vortex in the upstream area of the volute tongue in the impeller, and there is an obvious reverse flow from the blade outlet to the inlet near the volute tongue There are gap vortices in the gap In this paper, the axial distribution curves of velocity and static pressure at some typical positions are given In order to verify the reliability of this calculation method, the calculated flow and pressure characteristic curves are compared with the experimental results, and they are in good agreement Key words: CFD; multi wing centrifugal machine; 3D; figure classification number in numerical analysis: 035 document identification code: a article number: 0253 -- 231x (2003) 03-0419-04 the dimensional numerical analysis of multiplate fan you bin e e elhadi Xie Jun Long Wang Jun Wu Ke - (AI (School of energy and power engineering, Huazhong univeris wonderful of Science & technology, Wuhan 430074, China) Abstract Three-dimensional numerical analysis was carried out for a forward curved multiblade fan, the results showed that the maximal pressure in the volute distributed at different circumferential position along the axial direction An inlet vortex existed at upstream of the tongue in the interior region of impeller There existed obvious reverse flow from the blade outlet to the blade inner region near the tongue; and a clearance vortex existed at the tongue clearance The velocity and static pressure distribution along the axial direction at some typical point were given To validate the numerical methods, the calculated pressure characteristic curve was compared with the experimental data, they has good agreement Key words CFD multiblade fan; Because of its compact structure, high pressure coefficient and low noise, multi wing centrifugal fan is widely used in household appliances, air conditioning and various ventilation and air exchange occasions As we all know, the internal pressure fluctuation, wake, boundary layer separation and vortex shedding have a great influence on the aerodynamic and noise characteristics of multi wing centrifugal fans; At the same time, due to the asymmetry of the volute and its internal flow field belong to the three-dimensional flow of full viscosity, it is very limited and difficult to test some flow phenomena between the blades accurately by the existing experimental means For the research of multi wing centrifugal fan, most of the research reports that I have seen at present are about the aerodynamic characteristics experiment and the optimal configuration of impeller and shell; in the numerical simulation analysis, the CFD analysis of multi wing centrifugal fan is basically two-dimensional [2-6], the writer has not seen the analysis report of three-dimensional CFD of the whole multi wing centrifugal fan In this paper, the commercial CFD software is used to analyze the three-dimensional internal flow field of the multi wing centrifugal fan The numerical results show that the large pressure of Zui in the volute is distributed in different circular positions along the axial direction; there is an inlet vortex in the upstream area of the volute tongue; there is an obvious reverse flow from the blade outlet to the inlet near the volute tongue, and there is a gap vortex in the clearance between the volute tongue; The calculated flow pressure curves and the axial velocity distribution characteristics of some typical positions are in good agreement with the experimental results 2 Configuration of multi wing centrifugal fan the multi wing centrifugal fan selected in this paper is a small multi wing fan, the outer diameter of impeller Da = 140 mm, the ratio of wheel to shaft =0.857, impeller outlet angle hot OO = 1750, impeller inlet angle 0100 = 900, blade number Z = 43, blades evenly distributed along the circumference, impeller axial width H = 57 INM, worm tongue clearance 7.3% The configuration of impeller and volute is shown in Figure 1 In order to control the mesh quality, the complex 0-calculation area is divided into three parts: impeller internal area, blade channel area and volute internal area Each area generates a suitable mesh separately The adjacent areas share the same surface and share the same mesh nodes The mesh number of each area is 212914, For 533634 and 320625 nodes, prismatic pentahedral grid is used for grid shape, and rectangular grid is used for blade one and volute along axial surface respectively 4 The Navier Stokes equation of three-dimensional Reynolds average conservation form is used in the numerical solution The k-1: standard two equation model is selected as the turbulence model, and the standard wall function is used near the wall cftl The calculation method adopts the segrated implicit method, the turbulent kinetic energy, the turbulent dissipation term and the momentum equation are all discretized by the second-order upwind scheme; the pressure velocity coupling adopts the simple algorithm The continuity equation and momentum equation are written in tensor form as follows: the three-dimensional numerical analysis of multi wing centrifugal fan - 25 boundary conditions: according to the actual operation of multi wing centrifugal fan, the total pressure of impeller inlet is given as OPA, turbulence intensity and hydraulic diameter boundary conditions; the outlet of volute is given as static pressure boundary conditions; The impeller adopts the rotating coordinate, and the given boundary condition of the rotating wall is 2500 R / nun; the volute adopts the static coordinate, and the given boundary condition of the standard wall 6 Calculation results and discussion in this paper, the flow pressure characteristic curve of the plant is obtained by changing the outlet pressure boundary condition Figure 2 shows the comparison results between the calculated flow pressure curve and the experimental value ['], which is in good agreement When the flow difference between the impeller inlet and the volute outlet is less than 10-s, the calculation converges The following is a discussion on the flow characteristics of the J? Condition (flow coefficient Lao 20.253) near the Zui rate point Fig 3 is the cloud chart of static pressure and total pressure distribution of / 20.001 section (intake side) It can be seen from the figure that from the inlet to the outlet of the blade, due to the continuous increase of static weight and total pressure due to the work done by the blade, the Zui large static pressure and total pressure are near the wall of the volute On this section, the Zui large pressure in the inner part of the volute is approximately located at the position of the circumference 210 The total pressure near the pressure outlet decreases due to the flow loss, but the static pressure increases gradually due to the expansion of volute Fig 4 is a cloud chart of full pressure in section = 0.02 $5 (middle section) and / 20.056 section t hub side) From Fig 1, it can be seen that in the middle section, the Zui large pressure in the volute is located at the positions of 1200 and 2700 in the circumference, while in the section near hub side, the Zui large pressure in the volute is moved to the position of 3000 in the circumference, while in the section near the intake side, the Zui large pressure in the volute is moved to the position of 3000 in the circumference Three positions are located near the circumference 2100 (Fig 3), so we think that the large pressure of Zui inside the volute moves along the circumference in the axial direction and changes its distribution position and size Fig 5 is a cloud chart of velocity and dynamic pressure on the middle section It can be seen from the figure that the closer the impeller is to the leading edge of the blade, the higher the dynamic pressure and speed are This is mainly due to the continuous adsorption of the high-speed rotating impeller on the air flow inside the impeller The high dynamic pressure and speed of Zui are located in the outlet direction of the outer volute shell of the impeller, that is, +, as shown in Fig 1 As a result, it is located in the upstream area of the volute tongue inside the impeller, and there is an obvious inlet vortex at the leading edge of the blade inlet On the section near the hub side, the inlet vortex basically disappears due to the influence of the hub wall Figure 6 is the velocity streamline diagram of section = 0.019, private z = 0.056, which shows the dynamic characteristics Fig 9 is the distribution curve of static pressure and speed at the blade outlet along the axial direction The positions D, e and F of the monitoring points are y, X and + respectively The specific coordinates are a (0, - 0.073), B (- 0.073,0), C (0,0.073) It can be seen from the figure that the speed at the blade outlet increases gradually along the axial direction, while the static pressure changes gently along the axial direction Because of the asymmetry of the volute, the exit velocity and static pressure of the blade are different in different circular positions, and their changing trend along the axis direction also changes Because of the existence of the eccentric volute, it is difficult to show the real flow situation of the multi wing centrifugal fan by using the two-dimensional flow field or the calculation results of a blade passage to investigate the flow characteristics of the whole flow field The axial distribution characteristics of the inlet and outlet velocity and radial velocity calculated in this paper are basically the same as the test results in reference! 1], and the calculated results are basically consistent with the experimental results Conclusion in this paper, Navier Stokes equation and k-1-2 turbulence model are used to analyze the internal flow field of multi wing centrifugal fan The results show that there is an obvious three-dimensional flow in the multi wing centrifugal fan The results show that the Zui pressure in the volute is distributed in different circular positions along the axial direction There is an inlet vortex in the upstream area of the volute tongue in the impeller, and the inlet vortex basically disappears near the hub due to the influence of the hub There is an obvious reverse flow from the blade outlet to the inlet near the volute tongue, and there is a gap vortex in the volute tongue gap The gap vortex reduces the effective flow channel of the volute tongue gap, and the air flow in the volute tongue gap shifts to one side of the volute tongue; The numerical calculation of a blade channel or a section of a multi wing centrifugal fan is difficult to truly reflect the real chamber flow characteristics of the fan (L "Susumu Yamazaki, Katsuhiko Hashimoto, Yoshinori Fukasaku Influence of shape change of impeller and scroll in the axial direction on performance and noise for multiblade blower JSME, B, 1997, 63（614）: 125-129 !2〕 Shigetoshi Yamamoto, Fumiyasu Kuratani A Study on the Performance Improvement of Multiblade Fans JSME, B, 1999, 65（635）: 220-226 [3} Sandra Velarde-Suarez, Rafael B T, Carlos S M, et al Unsteady Flow Pattern Characteristics Downstream of a Forward-Curved Blades Centrifugal Fan Journal of Flu- ids Engineering, Transactions of ASME, 2001, 123: 265 270 114] J J Im, Y J Moon, Y D Choi Experimental Measure- menu of the Three-dimensional Flow Field in Sirocco Fan The Fifth Asian International Conference on Fluid Machinery, Seoul, Korea, 1997, 803-808 [5」 Tsutomu Adachi, Naohiro Sugita, Satoshi Ohomori Study on the Design of Impeller and Volute Casing of A sirocco fan In: the 4th International Conference on pumps and fans Beijing, 2002 198-205 (6) Wang Jun research on the internal flow characteristics of air conditioning fans: a post Research Report} Wuhan: Huazhong University of science and technology, 2002