Experimental and numerical analysis of vibrations in impeller of centrifugal blower
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Centrifugal blowers are widely used in different industrial applications nuclear and petrochemical, which are proficient of as long as restrained to high pressure rise and flow rates. Design of such impellers is important with noise reduction and maximum efficiency. In present work, an experimental and numerical analysis is done to study the effect of impeller blade thickness and rotating speed on the performance of the impeller. Different blade thickness has been considered with different rotating speed. A modal analysis is done for the numerical study using commercial software ANSYS Workbench. The numerical results are validated with experimental results found in test. The six different mode shapes are found in numerical study. The natural frequency and the total deformation is calculated for different blade thickness and rotating speed. The results shows that, the blade with 1.5 mm thickness has a reduced noise and vibrations with maximum rotating speed.
KeywordsFEA Impeller blade Inconel alloy 740 Vibration Weight optimization
Impellers are widely used in many centrifugal components of the nuclear and petrochemical industries. These applications requiring the high speed flow, small in size, low noise and low cost. In particular, these impellers are used majorly air flow applications. Hence, there is need of reduction of the noise, while using these impeller in such applications. The fluid kinetic energy generated by the impeller creates the pressure in whole system which causes the noise and vibrations. Centrifugal blowers having mainly two main parts, namely, casing and impeller. The impeller is often considered an integral part of the suction motor since its housings and the motor are assembled as a unit. The design of such impellers is important with balancing for noise reduction. The major reasons of the noise in such impellers are (1) The large inlet gap between the inlet nozzle and impeller shroud, (2) improper balancing of the impeller, and (3) improper matching between the impeller outlet and volute tongue . The designers of such impellers are encouraged by selection of the smaller, less noisy, and efficient. Several studies getting attentions towards the numerical and experimental studies for effect of noise and reduction of the noise level in such applications. Ramamurthi and Balasubramanian  did a steady state stress analysis of an impeller blade used in centrifugal fan. Cyclic symmetric structures were considered for the analysis. A finite Element analysis (FEA) tool is used for the analysis. Impeller stresses were measured using strain gauge technique and numerical results were compared with these results. Elyamin et al.  investigated the effect of number of impeller blade on the performance of the centrifugal pump numerically. Three different impeller with different number of impeller blades 5, 7 and 9 were considered for the analysis. Authors found that, the highest efficiency for the 7 number of blades and the overall loses deceases by increasing number of blades. Srivastava et al.  presented a numerical investigation of the mixed flow pump impeller blade with stress analysis. A design and stress analysis had been done to find out the effect of blades on the pump with different position in meridional annulus. The results of von misses stress were compared among the different blade position. The inclined blades at the inlet were found to be more suitable for the overall performance. Mane et al.  did a study on the M.S. impeller used in centrifugal pump using finite element analysis (FEA) method. A simple impeller model had been designed and analysed using the commercial software ANSYS. A simple modal analysis is done to measure the frequency (Hz) with respective rotating speed. From the results, It was found that the vector displacement of the impeller increased by increasing natural frequencies.
Ashiri et al.  did a dynamic modal analysis of impeller blade. A natural frequency and the mode shapes were studied for the different operating conditions. A single entry radial vane impeller had been considered for the modal analysis. Modelling and analysis were carried out using ANSYS Bladegen and ANSYS workbench. The results found that, there is a minimal effect of impeller blade thickness and impeller blade on the frequency. Mohonty and Rixen  developed a modified SSTD method for measurement of the harmonic excitements in a common modal analysis. Harmonic excitation can happened due to rotating components viz. unbalanced rotor and fluctuating forces etc. The purposed method which were considered a purely harmonic vibrations.
Mane et al.  did a FEA study on the design and analysis of the centrifugal pump impeller. A modal analysis had been done for the measurement of the natural frequency. A two different materials viz. Aluminum and Inconel 625 of the impeller were considered for the modal analysis. The results shows that, a maximum deformation were found in aluminum material under similar conditions while there was minimal effect on the natural frequency on these material change. Zhang et al.  did a numerical study to find out the effect of weld heat treatment on the residual stress in welded impeller. Based on results they were concluded that, circumferential residual stress in the impeller was found higher than the vertical residual stress. Lu et al.  presented numerical optimization on the vibroacoustics of a centrifugal volute impeller. An optimization was carried out using local thickness variation and experiments are conducted and results are compared with numerical results, which were found good agreement. A natural frequency and total deformation was extracted for the optimization of the volute fan. The results are used for the designing of such type of impeller. Fehse and Niese studied a generation mechanism of low frequency noise of a centrifugal fan. Different experiments had been performed with five centrifugal fan impeller and they found reduced flow separation, reduced noise, more uniform flow with less turbulence [11, 12].
Liu et al.  did a FEA study on analysis of the impeller life by considering centrifugal load and aerodynamic load. This study was established as a reliable by comparing experimental results with FEA results. Jayapragasan et al.  has selected Parameters for optimization is—fan outer diameter, number of blades and fan blade angle. Taguchi’s orthogonal array method helps to find out the optimum number of cases and the modelling has been carried out using SOLIDWORKS. ICEM CFD is used for meshing the blowers and analysing using FLUENT. The results are showing that the optimum combinations are 190 mm outer diameter, 80° blade angle and 8 numbers of blades.
Parshi et al.  did the study to increase the life period of centrifugal blower impeller by considering different types of materials, designs and by varying the thickness of base plate of centrifugal blower impeller. Using ANSYS software implemented static analysis under different boundary conditions also implemented Taguchi optimization technique to grab the best material, design and thickness. They found optimum total deformation for 12 number of blades and 8 mm blade thickness.
2 Mathematical model
The first step in the impeller design is to select relative speed as per the requirement of head and flow rate conditions. This establishes the specific speed or type of the impeller. Selection of the speed is governed by a number of considerations: (1) Type of driver contemplated for the unit. (2) Higher specific speed results in a smaller blower and cheaper drivers. (3) Optimum hydraulic and total efficiency possible with each type varies with the specific speed.
2.1 Selection of impeller type as per specific speed
2.2 Design steps
Minimum impeller inlet diameter (d1)
Impeller outside diameter (d2)
Shroud diameter (ds)
Area of Shroud (As)
Impeller inlet blade width (b1)
Impeller inlet area (A1)
Summary of calculated values
Minimum impeller inlet diameter (d1)
Impeller outside diameter (d2)
Eye or shroud diameter (ds)
Area of shroud (As)
Impeller inlet blade width (b1)
Impeller inlet area (A1)
Blade peripheral velocity at inlet (U1)
Absolute velocity at impeller inlet (V1)
Blade angle at impeller inlet (β1)
Relative velocity at impeller inlet (W1)
Impeller outlet blade width (b2)
Impeller outlet area (A2)
Outlet blade velocity (U2)
Radial component of outlet velocity (Vr2)
Blade exit angle (β2)
Tangential component of outlet velocity (Vu2)
Absolute velocity at impeller outlet (V2)
Relative velocity at impeller outlet (W2)
Diameter ratio (€)
Number of blades (Z)
Slip factor (µ)
Actual exit velocity peripheral component due to slip (Vu2′)
Actual absolute exit velocity (V2′)
Actual relative velocity (W2′)
Actual blade exit angle (β2′)
Actual air exit angle (α2′)
Air velocity at impeller eye (Veye)
Loss factor (K1)
Pressure loss at impeller entry
Air density (ρ)
Loss factor (Kii)
Pressure loss in impeller blade passages
Pressure/head coefficient (ψ)
Flow coefficient (ø)
2.3 Selection of parameters
Parameters for experimentation
2.4 Statistical analysis using ANOVA technique
3 Experimental setup
Impeller material properties
MS (IS 2062)
Young modulus (MPa)
2.21 × 105
2.07 x 105
Figure 4 shows photograph of manufactured impeller which is used in the proposed study.
3.2 Casing of the blower
The component contains the impeller is generally called as the casing [21, 22, 23]. A rotating instrument comprises of suction as well as a discharge penetration for the rotating instrument like pumps in main flow path. The pump or blowers normally has vent fittings and small drain to eliminate gases confined in the casing. The casing of the blower used is shown in Fig. 5. In addition, it also performs few other important functions viz. (1) Provides pressure containment, (2) incorporates the collector, (3) allows rotor installation and removal, (4) maintains the alignment of the pump and its rotor under the action of pressure, (5) supports the pump and reasonable piping loads.
3.4 SVAN 974 vibration analyzer
3.5 Experimental procedure
Selected performance parameters for the analysis
Thickness of impeller blade (mm)
Rotating speed (RPM)
4 Numerical analysis
Velocity is given in Z axis,
Initial velocity is given as 100 rpm
Final velocity is given 2850 rpm
X, Y component—free
Z component—0 mm
X, Y rotation—free
5 Results and discussion
5.1 Validation of the numerical model
The analysis has been performed to study the effect of impeller blade thickness on the natural frequency and total deformation of the impeller blade. Three different impeller blade thicknesses have been chosen viz. 1.5 mm, 2 mm and 3 mm for the weight optimization of the impeller. A natural frequency and total deformation has been calculated for three different blade thicknesses. Six different mode shapes have been plotted for each case of impeller blade. The result shows that, as the increase in thickness of the blade the natural frequency increased, while the total deformation reduced. The maximum natural frequency found 364.05 Hz, while minimum total deformation of 16.28 mm for 3 mm blade thickness and 2850 rpm.
The vibrations are presents in impeller while rotating high speed, found maximum at the motor base of the impeller than the cover front and top of the impeller casing.
Thickness of the blade has a greate influence on the impeller performance. Vibrations can be controlled with selection of optimum blade thickness. Thickness of impeller blade was reduced from 3 mm to 1.5 mm with changing the rpm of rotation 2550, 2650, 2750.
The total deformation has reduced up to a certain speed and thickness after that the defoemation and frequency has been increased.
The maximum deformation of Inconel 740 impeller is 11.522 mm for 2750 RPM, 1.5 mm blade thickness with natural frequency of 8.27E−04 Hz.
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