Design Optimization of Aerofoil Bladed Radial Fan

Design Optimization of Aerofoil Bladed Radial Fan

1R. Ramanjaneyulu, Academic consultant, Dept. of Mechanical Engg,

Y.S.R Engineering college of Y.V.U,

Proddatur.

2P. Srinivasula Reddy, Academic consultant, Dept. of Mechanical Engg,

Y.S.R Engineering college of Y.V.U,

Proddatur.

3T. Murali, Academic consultant,

Dept. of Mechanical Engg,

1. Engineering college of Y.V.U,

   Proddatur

   Abstract: The aim of the project work is design optimization of Aerofoil bladed radial fans through finite element analysis. The cost of the present impeller is very high due to its massive weight. The design and analysis is carried out for the present impeller of Aerofoil bladed radial fan. Both Static and modal analysis is performed to determine the stress distribution, maximum stress induced, maximum deflection and the nature frequency. Design and Analysis is done by commercial software Ansys.

   Key words: Radial fan, Ansys.

   1. INTRODUCTION

      Most manufacturing concerns spend more than a 60% of their money for materials, i.e., material soak up substantial portion of the capital invested in an industrial concern. This emphasizes the need for adequate material management because even a small saving in the material can reduce the production cost to a fair extent and thus add to the profits. The analysis is carried out in ANSYS. The analysis was carried out in two phases comprising of static and modal analysis. Static analysis consists of finding the deformation under loading, the strains and the working stresses. The modal analysis consists of predicting the natural frequency of vibration of the rotating impeller.

      The objective of this study was to optimize the weight of the radial fan by using commercial software Ansys.

   2. DESCRIPTION OF FANS

      Fans are one of the turbo machines used for energy transfer. The main aim of a fan is to move a gas without an appreciable increase in its pressure. The total pressure developed by fans is of the order of a few millimeters of water gauge (W.G.). The flow is continuous because the flow at entry and exit and also through the impeller is steady.

      Classification of Fans:

      The fans are classified as according to the direction of the flow of the fluid with respect to the fan axis. The schematic representation of different kinds of fans are shown in Figure1.

      Figure1: Schematic representation of different kinds of fans

      Axial flow fan: The flow is parallel to the axis of rotation of the fan both at entry and exit. Axial fans may be classified further into impulse type and reaction type fans.

      Radial fan: The fluid enters into the rotating element (rotor) perpendicular to the axis of rotation. The schematic representation of radial fan shown in Fig2.

      Figure 2: Radial fan

   3. SELECTION OF FANS

      The fans are commonly utilizing in power plants, ventilation systems and cooling of electric motors and generators [3].

      The guide lines for selection of fans are as follows.

      1. The operating point should lie in the peak efficiency zone at the highest possible vane or blade opening.

      2. The maximum operating speed should be chosen so that the unit size is small.

      3. The operating parameters selected should not lie in the unstable zone or even close to the stall line. It should be ensured that the system resistance curve does not cut the stall line and enter the unstable zone.

      From the above guide lines we are chosen radial fan.

   4. SELECTION OF MATERIAL

      The material chosen for above mentioned radial fan is NAXTRA 70. The properties of above material are Poissons ratio is 0.3, density is 8.002E-10kg/mm3 and youngs modulus is 21000kgf/mm2[1]. The impeller is rotated at 1000 rpm. Geometrical parameters of the existing and modified impeller are shown in Table1 and Table 2 and aerodynamic parameters are shown in Table 3.

      Table 1: Geometrical parameters of existing model

      Table 2: Geometrical parameters of Modified Model

      Table 3: Aerodynamic parameters

   5. NUMERICAL SIMULATION

      For numerical simulation the above mentioned radial fan is selected. The operating speed is taken as 1000 rpm and angular velocity is 104.67 rad/sec[2]. and an iterative solver is chosen for simulation. The thickness of the model is reduced up to 20% of the existing design. The mesh generation and design of the mode accomplished by commercial software Ansys[2], this uses finite element method. The schematic representation of model diagram shown in figure 3.

      Figure 3: Model diagram of Radial fan with meshing

   6. VALIDATION

      The variables stress, deflection, mass and cost are validated with existing design, the variations are shown in below Table. The variation in mass and cost of the impeller shown in figure 8 and 9.

   7. RESULTS AND DISCUSSIONS

Thus we have done the iterative analysis on the impeller by reducing the thickness of all parts of impeller in steps 2% and finally we end up with a maximum reduction of 20% thickness with all constraints satisfied. The stress distribution on the modified impeller and cover plate as shown in figures 4 and 5. The maximum stress induced and also the maximum deflection is examined. Actually the stress induced in Cover Plate (11.7kgf/mm2) is maximum of all and it is within the maximum allowable stress 12.5kgf/mm2. The maximum deflection occurs in Cover Plate (0.27mm) which is also within the allowable limit of 0.3mm. Thus the constraints are satisfied and the design is safe. The natural frequency of the modified model is reduced than existing model shown in Figure 6 and 7. From figures 8 and 9 mass and cost of the modified model decreasing rather than existing model.

Figure 4: Stress distribution in the impeller

Figure 5: Stress distribution in the cover plate

Figure6: Natural frequency of existing model

Figure 7: Natural frequency of modified model

Figure 8: Mass comparison

Figure 9: Cost comparison

IX CONCLUSIONS

1. The value of the product can be increased either by increasing its utility with the same cost or by decreasing its cost for the same function

2. The cost and weight of the radial fan is decreases without changing its usefulness.

3. From static and modal analysis when decreasing the thickness of the radial fan the weight and cost both are reducing and at the same time frequency is decreasing, stress and deflections are increasing.

X. REFERENCES

1. P.S.G data Handbook, Design data., PSG college of Technology.

2. Zienkiewicz. O. C., Irons, B. M. scott, F.C., and Campbell, J. S., Three dimensional stress analysis, Proceedings, Symposium on high speed computing of elastic structures, University of Liege, Belgum.

3. Engineering cook book, A hand book for the Mechanical designer, Loren cook company, Springe field, MO.

4. www. Ansys.com