Static and Dynamic Analysis of A Centrifugal Blower Using Fea

Static and Dynamic Analysis of A Centrifugal Blower Using Fea

Veeranjaneyulu Itha1, T.B.S.Rao2

1. M.Tech (Machine Design), Mechanical Engineering Department, Nimra Institute of Science & Technology, Ibrahimpatnam, Vijayawada, Andhra Pradesh, India.

2. Professor & H.O.D of Mechanical Engineering department, Nimra Institute of Science & Technology, Ibrahimpatnam, Vijayawada, Andhra Pradesh, India.

ABSTRACT

Centrifugal blowers are used extensively for on- board naval applications have high noise levels. The noise produced by a rotating component is mainly due to random loading force on the blades and periodic iteration of incoming are with the blades of the rotor. The contemporary blades in nava applications are made up of aluminium or steel and generate noise that causes distrubance to the people working near the blower.

The present work aims at examining the choice of composites as an alternative to metal for better vibration control. Composites, known for their superior damping characteristics are more promising in vibration reduction compared to metals. The modeling of the blower was done by using solid modeling software, CATIA V5 R19. The blower is meshed with a three dimensional hex8 mesh is done using HYPERMESH 10.

It is proposed to design a blower with composite material, analyze its strength and deformation using FEM software. In order to evaluate the effectiveness of composites and metal blower using FEA packaged(ANSYS). modal analysis is performed on both Aluminium and composite blower to find out first 5 natural frequencys .

Keywords : CATIA V5 R19, HYPERMESH 10,

ANSYS.

1. INTRODUCTION

   Blowers are one of the mechanisms used regularly in submarines. They are installed in ventilation and air conditioning systems in almost all submarine compartments. Ventilation systems usually presented by central systems include supply and exhaust fans, serve for ventilation of accommodation and other than accommodation areas with atmospheric air with simultaneous ventilation of storage batteries and for air cooling and purification from harmful and smelling impurities. Air conditioning systems are presented by local, compartment group and single duct systems. These systems are used to provide comfortable conditions in terms of air temperature and humidity for the crew in accommodation areas and other accommodation areas, air purification in galleys, provision rooms, and sanitary areas and also for air mixing in compartments.

   All blowers intended for submarine installation differ from industrial ones not only for their high reliability and strength under dynamic impacts but also for low noise and vibration levels. As blower represents a large part of submarine mechanisms, they should naturally meet the following compulsory requirements for all mechanisms:

   1. Minimum weight-dimensional parameters.

   2. Reliable operation at submarine motions.

   3. Vibration and impact resistance.

   4. Convenience of mountings, repairs and easy access to lubrication points.

   5. Keeping of service life at transportation and changes in climate.

2. CAUSES OF NOISE GENERATION IN CENTRIFUGAL BLOWER

   1. Tonal noise caused by rotational frequency and fan blade passing frequency (BPF) and their harmonics. These are usually the noise source.

   2. Broadband aerodynamic noise generated by airflow at the inlet and outlet of the cooling fan.

   3. Mechanical noise caused by friction in bearings and seals, vibration due to motor fan static and dynamic unbalanced rotating masses, resonant vibration of motor- fan casings, motor fan mounting and misalignment, etc. 4.Electromagnetically generated noise caused by changing of electromagnetic field in the electric motor.

3. NOISE CONTROL TECHNIQUES

   Environmental noise usually does not emanate directly from the energy source rather, it transmitted along mechanical or liquid paths before it finally radiates from some vibrating surface into the surrounding environment. The approaches to treating pump noise generally include the following:

   1. Modify the basic design or operating condition to minimize the generation of acoustic energy.

   2. Prevent sources from generating airborne noise by interrupting the path between the energy source and the listener. This approach may range from isolation mounts at the source to physically removing the listener.

4. ROLE OF COMPOSITE MATERIALS IN NOISE SIGNATURE CONTROL

Composite material is a system that is created by the synthetic assembly of two or more materials. The

material consists of fiber of high strength and modulus embedded in a resin with distinct interfaces between them. They produce a combination of properties that cannot be achieved with either of the constituents acting alone. Composite materials have high strength, modulus.

The most common form in which reinforced composites are used in structural application is called a laminate and it is obtained by stacking a number of thin layers of fibers and matrix and consolidating them into the desired thickness. Fiber orientation in each layer and stacking sequence of various layers can be controlled to obtain a wide range of physical and mechanical properties for the composite laminate.

These materials are found to have high damping co-efficient. The damping property of a material represents its capacity to reduce transmission of vibration caused by mechanical disturbances to a structure. The measure of damping of a material is its damping factor. Increasing the value of is desirable for reducing the resonance amplitude of vibration in a structure. Damping factor value depends on a number of factors, including fiber and resin types, fibre orientation angle, and stacking sequence.

1. HEADINGS

2. PRINCIPLE OF CENTRIFUGAL BLOWER

   Operating principle is a combination of two effects: Centrifugal force which produces more static pressure and again deflection of the air flow by the blades, but here the deflection is from a radially outward direction into a spiral flow pattern. In case of forward curved blades the air deflections have a strong influence on the flow pattern and on the performance.

3. PROBLEM DEFINITION

   In the present problem, metal blower is used for air conditioning and ventilation purpose in naval defence applications causes vibration and noise during its operation which causes mental imbalance to the people working near the blower on ship. Therefore reducing vibration from a source is very important and critical task. Hence the objective of this project is to reduce the vibration level produced by metal air blower. It can be effectively reduced by the modifying the shape of blades.

4. BRIEF DESCRIPTION OF THE PRESENT WORK:

Finite element method is the most versatile of all numerical techniques available. Hence the blowers have been analyzed by the Finite Element Analysis technique (FEA). For the purpose of finite element analysis, the commercially available finite element package, ANSYS 11.0 has been used. The study of centrifugal blowers includes modeling and analysis.

1. STEPS INVOLVED IN THESIS

2. MODELING BY USING CATIA V5 R19

   A centrifugal blower with rearwardly curved impeller blades positioned in housing between two housing faces that are spaced apart along the impeller axis. One of the housing faces defines a housing inlet

   p>called bell mouth. The housing is substantially closed off with the exception of the inlet and an outlet. Modeling of the Centrifugal blower is done using CATIA V5 R 17. In order to model the centrifugal blower it is necessary to model the parts of the blower which are Spiral Casing, Impeller and the suction plate then it was assembled to get the total component. The solid model of the centrifugal blower is as shown in the figure.

3. MESHING BY USING HYPERMESH 10.0

   The solid model is imported to HYPERMESH 9.0 and hexahedral mesh is generated for the same. The meshed model is shown in figure 5.2. The meshing was done by splitting it into different areas and the 2D mapped mesh was done and then it was converted into 3D mesh using the tool linear solid. The number of elements and nodes are 27,388 and 52,412. Quality checks are verified for the meshed model. Jacobian, warpage and aspect ratio are within permissible limits. Then the meshed model is imported into the ANSYS.

   Apply boundary condition given in 6.3

   Enter the ANSYS solution processor in which analysis type is taken as modal analysis, and 'by taking mode extraction method, by defining number of modes to be extracted. Solution method is chosen as Block lanczos method.

   Solve the problem using current LS command from the tool bar.

   Procedure for harmonic analysis

4. ANALYSIS OF CENTRIFUGAL BLOWER

The analysis of centrifugal blower has been carried out by using ANSYS 11.0 general purpose FEM software. The following analysis were done on the blower

1. Static analysis

2. Modal analysis

3. Harmonic analysis

Procedure for Static analysis in ANSYS

Build the FE model as explained in chapter 5.

Define the material properties such as young's modulus and density etc.,

Apply boundary condition and pressures as given in 6.3.

Solve the problem using current LS command from the tool bar.

Procedure for modal analysis in ANSYS

Build the FE model explained in chapter 5.

Material properties such as Young's modulus and density are defined.

Apply the constraints and pressure as explained in 6.3.

Enter the ANSYS solution processor in which new analysis is chosen as harmonic response and solution method is full method

For this analysis the solution technique used is frontal solver.

By defining the frequency range as 0-500 Hz with 150 sub-steps.

Solve the problem using current LS command and obtained the results.

1. INDENTATIONS AND EQUATIONS

2. UNIDIRECTIONAL CONTINUOUS FIBER 0º LAMINA

   Longitudinal modulus = E11 = Ef Vf + Em Vm Major Poissons ratio = 12 = f Vf +m Vm

   Build the FE model explained in chapter 5.

   Transverse Modulus = E22 =

   Ef Em

   Define the material properties such as young's modulus and density etc.,

   Ef VM EMVF

   Minor Poissons ratio = 12 =

   Shear Modulus = G12 =

   Gf

   E22

   E

   12

   11

   Gf Gm

   m Gm f

   5.2 to 5.5. Table 5.1 shows induced deformations and stresses in aluminum blower.

   Table 5.1 Static analysis results of Aluminium blower

   Aluminium Blower	Results
   Deflection in mm	0.0914 mm
   Max. Normal stress, N/mm2	3.483 N/mm2
   1st principal stress, N/mm2	13.234N/mm2
   2nd principal stress, N/mm2	1.345N/mm2
   3rd principal stress, N/mm2	0.9047N/mm2

3. MATERIAL PROPERTIES OF THE BLOWER

The analysis is performed on (i) Metallic blower and (ii)Composite blower

1. Material properties of metallic blower: (aluminium)

   Youngs modulus E= 70000 MPa Poissons ratio NUXY=0.34

   Mass density =2700 kg/m3 Damping co-efficient =0.006

2. Material properties of composite blower: ( Glass/epoxy)

Youngs modulus Ex = Ey = 14Gpa, Ez = 8.8Gpa Poissons ratio NUXY= 0.13, NUYZ=NUZX = 0.39

Shear modulus Gxy = 4.7Gpa, Gyz=Gzx = 4.2Gpa Mass density =1750 kg/m3

Damping co-efficient =0.02

1. RESULTS & DISCUSSIONS

   1. STATIC ANALYSIS OF ALUMINIUM BLOWER

      The deformation of aluminium blower is shown in figure5.1 and the maximum deflection was found as 0.0914 mm. The maximum normal stress obtained is 3.483 N/mm2. The stress and displacements are shown in figures

      The maximum deflection induced in metallic blower is 0.0914 mm , which is in safe limits. Hence based on rigidity the design is safe. The maximum induced stress is 13 Mpa which is less than the allowable stress (160 Mpa).Hence the design is safe based on strength.

      Fig. 5.1 Deformation of aluminium blower, mm

      Fig. 5.2 Stress of Aluminium blower in Z-direction, N/mm2

      Fig.5.5. 3rd Principal Stress of Aluminium blower, N/mm2

   2. STATIC ANALYSIS OF COMPOSITE BLOWER

Static analysis of composite blower is carried out so as to check the bonding strength between various layers of composite blower and Inter-laminar shear stresses are calculated.

Fig.5.3. 1st

Principal Stress of Aluminium blower, N/mm2

Maximum deflection for composite blower with 27 layers was found to be 1.018 mm as shown in figure

5.6. The maximum normal stress was found to be 4.534 N/mm2 in z-direction as shown in figure 5.7 and the maximum inter-laminar shear stress as 8.669 N/mm2 and is shown in figure 5.8. Table 5.2 shows induced deformations and stresses in composite blower.

Fig.5.4. 2nd Principal Stress of Aluminium blower, N/mm2

The deflection for composite blower was found to be around 1.018 mm for all layers which is more than that of Aluminum blower i.e. 0.0914mm.Interlaminar shear stresses were calculated for composite blower for 27 layers and the maximum interlaminar shear stress is found on the layer 27.

Results

Table 5.2 Static analysis results of composite blower

Composite blower (27 layers)

Fig. 5.8. Maximum interlaminar shear stress (occurs between LN1 and LN2), N/mm2

5.3. EIGEN VALUE ANALYSIS OF BLOWER

Fig. 5.6. Deformation of composite blower, mm

Fig. 5.7. Stress of composite blower in Z-direction, N/mm2

Eigen value analysis results show that the first critical speed of composite blower is 94 Hz and that of aluminium blower is 128.11 the reduction in natural frequency of composite blower is due to the high stiffness of the composite blower as per the equation below. This shows that both composite and aluminium blower are running with in the safe limits. The natural frequencies of the experimental results match with the natural frequency in the table.

Table 5.3 Comparison of first ten natural frequency of aluminum and composite blower

Fig.5.9.First mode shape of Aluminum blower

5.12.Second mode shape of Composite blower

Comparison

Natural frequency

600

400

200 Metal

0

1. Second mode shape of Aluminum blower

   0 5 10 15

   No. of modes

   Composite

2. First mode shape of Composite blower

Fig.5.13. Natural frequency of Aluminum and composite blower

1. HARMONIC ANALYSIS OF ALUMINIUM BLOWER

   Harmonic response analysis is carried out on both aluminum and composite blower; it was observed that composite blower is performing well compared to aluminum blower. We can observe peaks at the natural frequency in both aluminum and composite blower. In composite blower the displacements are reduced when compared to the aluminum blower which shows that the acceleration of composite blower is less that causes lesser

   vibration in composite blower because in composite blower the damping controls the vibrations.

   The following advantages were observed from harmonic response analysis of composite blower over Aluminum blower:

   1. Vibration levels are less in composite blower compared to aluminum at higher frequency range.

   2. The maximum displacements are lesser in composite blower than aluminium.

   3. The mass of the composite blower is much less than aluminium.

Fig.5.14.X-Component of Displacement versus Frequency response graph of aluminum blower

Fig.5.15. X-Component of Displacement versus Frequency response graph of Composite blower

1. CONCLUSIONS

   The following conclusions are drawn from the present work

   1. The stresses of composite blower obtained in static analysis 4.534 N/mm2 are within the allowable stress limits.

   2. The natural frequency of composite blower is reduced because of high stiffness and the lay up sequence in the blower.

   3. The weight of the Composite blower is 15 kg which is less than the aluminum blower with a weight of 20 kg.

   4. From the results of harmonic analysis, damping effect is more in composite blower which controls the vibration levels.

2. FUTURE SCOPE OF WORK

In present work the harmonic analysis is carried out for both aluminum and composite blower and response is compared. The aerofoil blade profile may be used for impeller blade and further solution is required.

1. REFERENCES

   1. Huang Chen-Kang and Hsieh Mu-En, Performance analysis and optimized design of Backward curved airfoil centrifugal blowers, American society of Heating, Refrigerating and Air Conditioning Engineers, May 1, 2009

   2. Prezelj Jurij and Carudina Mirko, Identification of noise sources in centrifugal blower with acoustic camera, The Journal of Acoustical Society of America, Volume 123, Number 5, p. 3824, May 2008.

   3. J.B. Moreland, Housing effect on centrifugal blower noise, Journal of Sound and Vibration,

      Volume 36, Number 2, pp. 191-205,22

      September 1974.

   4. G. H. Koopmann and W. Neise, The use of Resonators to silence centrifugal blower, Journal of Sound and Vibration, Volume 82, Number 1, pp. 17-27, 8 May 1982.

   5. Renjing Cao and Jun HU, A cluster design approach to noise reduction in centrifugal blower, International Journal of Ventilation, Volume 3, Number 4, pp. 345-352, 2005.

   6. T. F. W. Embleton, Experimental study of noise reduction in Centrifugal Blowers, The Journal of Acoustical Society of America, Volume 35, Number 5, pp. 700-705, May 1963.

   7. Q. Datong, Mao Yijun, Liu Xiaoliang and Yuan minjian, Experimental study on the noise reduction of an industrial forward-curved blades centrifugal fan, Applied Acoustics, Volume 70, Number 8, pp. 1041-1050, August 2009.

   8. Sandra velarde, Rafael Ballesteros, Carlos Santolaria and Bruno pereiras, Reduction of aerodynamic Tonal Noise of a forward curved centrifugal fan by modification of the volute tongue geometry, FEDSM2005-77436, 2005 ASME Fluids Engineering Division Summer Meeting and Exhibition June 19-23, 2005, Houston, TX, USA

   9. Michel Tournour, Zoubida El Hachemi, Alex Read, Fred Mendonca, Fabio Barone and Paolo Durello, Investigation of tonal Noise radiated by subsonic fans using the Aero-Acoustic analogy, FAN NOISE 2003 International Symposium Senlis, 23-25 September 2003.

   10. Raymond A. Loew, Joel T. Lauer, Joseph McAllister and Daniel L. Sutliff, Advanced noise control Fan, Twenty-Fifth Aerodynamic Measurement Technology and Ground Testing Conference sponsored by the American Institute

       of Aeronautics and Astronautics, San Francisco, California, June 5- 8, 2006.

   11. Jeon Wan-Ho and Lee Duck-Joo, A numerical study on the flow and sound fields of centrifugal impeller located near a wedge, Journal of sound and vibration, Volume 266, Number 4, pp. 785- 804, 2003

   12. Christopher L. Banks and Sean F. Wu, Prediction and reduction of centrifugal blower noises Journal of Acoustical Society of America, Volume 103, Number 5, pp. 3045-3045, May 1998.

   13. Jianfeng MA, Datong QI and Yijun MAO, Noise reduction for centrifugal fan with non-isometric forward-swept blade impeller, Energy Power Engineers, Volume 2, Number 4, pp. 433437, 2008.

   14. M. Carudina, Noise generation in vane axial fans due to rotating stall and surge, Journal of Mechanical Engineering Science, Volume 215, Number 1, pp. 57-64, 2001.

   15. S. Kolla, Y. Anil Kumar and S. Rajesh, Noise reduction in air blower casing using composites, Springer Proceedings in Physics, Vibration Problems ICOVP-2007, Volume 126, pp. 215-222, October 2008.

   16. Rama Krishna Shinagam, Rama Krishna A and Ramji k, Experimental study on reduction of motor-fan noise by modification of blade and shroud configuration, Proceedings of the institution of Mechanical Engineers, Part C, Journal of mechanical engineering science, Volume 224, Number 2, pp. 315-320, 2010.

   17. Mohand Younis, Farid Bakir, Smaine Kouidri and Robert Rey, 3D unsteady flow in a centrifugal fan: impeller-volute interaction, Journal of Computational and Applied Mechanics, Volume 8, Number 2, pp. 211-223, 2007

   18. Gerald C. Lauchle, John R. MacGillivray and David

       C. Swanson, Active control of axial flow fan

       noise, The Journal of Acoustical Society of America, Volume 101, Number 1, January 1997.

   19. Buhei kobayashi, Satoshi Nakazawa, Shigehiro Onozawa and Toshiharu Sawada,

       Development of low-noise and large air volume type blower equipped with an environmental- friendly engine, Komatas Technical report, Volume 48, Number 149, 2002.

   20. Wan-Ho Jeon, A numerical study on the Acoustic characteristics of a centrifugal impeller with a splitter, GESTS Intl Trans. Computer Science and Engr., Volume 20, Number 1, October 2005.