A STUDY OF FLOW FIELD MEASUREMENTS OF RADIAL GAB WITH DIFFERENT RPM BY USING COMPUTATIONAL FLUID DYNAMICS

(1)

Volume III, Issue XI, November- 2016

13

A STUDY OF FLOW FIELD MEASUREMENTS OF RADIAL GAB WITH

DIFFERENT RPM BY USING COMPUTATIONAL FLUID DYNAMICS

1

*S.Senthilkumar , 2Dr.Ankur Awashthi 1

* Research Scholar,Department of Mechanical Engineering, Maharishi University of Information Technology, Lucknow

2

Associate Professor, Department of Mechanical Engineering, Maharishi University of Information Technology, Lucknow

[email protected], [email protected]

Abstract

A modern trend in flow analysis in slurry impellers has long been an concentrated subject of research. The Computational Fluid Dynamics (CFD) is the present day state-of-art technique for fluid flow analysis. It was found that Un-steady as follows are created in different part with modern design conditions which result in the decreasing efficiency different radial gaps. The operating characteristic curves by the numerical simulation of velocity vectors were c o m p a r e d w i t h t h e results o f model testing and are found in good agreement. The test case consists of an enshrouded centrifugal impeller with seven blades. A large number of measurements are available in the radial gap between the impeller and the diffuse, making this case ideal for validating numerical methods with velocity vectors. Results of steady and unsteady calculations of the flow in the slurry impellers are compared with the CFD experimental ones.

Keywords: Slurry impeller model, STANDARD K-ε Model, (RNG)K- ε Model.

1. Introduction

The slurry impeller is used to transport fluid by the

conversion of the rotational kinetic energy into the

hydrodynamic energy. The pressure at outlet is a

reflection of the centripetal force that curves the

path of the water and guide to move circularly

inside the slurry impeller. This force supplied by a

pressure gradient is set up by the rotation, and the

outside pressure, at the wall of the volute, can be

considered as a reactive centrifugal force.

2. LITERATURE SURVEY

For designers, the prediction of the operating

characteristics curve is the most important. An

optimum design consideration of a mixed-flow

impeller blade was the main focus of the research

by (Li et al 2012) and the analysis was carried out

using CFD improvement of the performance of the

designed impeller achieved by under-filing the

impeller blades at the trailing edge. The

investigators emphasized the need to integrate CFD

software to the design process on a continuous

basis. Further, some important considerations from

the manufacturing viewpoint were enumerated.

These include selecting the suitable blade and vane

thicknesses, blade swirl and vane angles.

3. RESEARCH OBJECTIVE

i. Achieving the very best practice of CFD to

(2)

International Journal On Engineering Technology and Sciences – IJETS™

ISSN(P): 2349-3968, ISSN (O): 2349-3976 Volume III, Issue XI, November- 2016

14 ii. To compare various turbulence models such

as K Epsilon RNG Model and K Epsilon

STD Model

4. DESIGN AND SPECIFICATION OF

THE SLURRY IMPELLER

Flow analysis of 200 m3/hour capacity of slurry

impeller is carried out using the CFD package

FLUENT is utilised. The salient features of the

slurry impeller are given in Table 1.

Figure 1 Slurry impeller vane dimensions Table 1 Salient features of the Slurry impeller

model.

Rated Head 20.1m

Rated Discharge 200m3/hr

Rated Speed

1000-2500rpm No. of impeller

vanes

7

Diameter of

impeller eye

150mm

Outer diameter of impeller

260mm

Blade thickness 6mm

Width of impeller at outlet

26mm

4.1. SLURRY IMPELLER MATERIAL

Housings thrust bearing base and oil seal housing

are made from FG200 graded cast Iron. Housing

journal brushes are water-imbricate head fin bronze

materials. Thrust bearings with segment and ball

type are used to ensure wide thrust heads. Winding

is made by poly wrap wires, which are cooled by

water. The parameters identified for this existing

impeller model is listed below in Table 2

Table 2 Specification of the impeller and bowl

Parameter Dimensions

Imp eller

Bowl

Inlet diameter (di)

mm 61

68-113 varying

(Taper length = 40) Outlet diameter(

do) mm 96 129

Inlet blade angle 82° 55.29° Outlet blade angle 57° 29.45°

Thickness of

blade(t) mm 1.85 15

Number of blades

(n) 6 8

5. COMPUTATIONAL FLUID DYNAMICS

5.1. METHODOLOGY

1. During pre-processing

 Define the geometry of the problem.

 The occupied volume by the fluid is

suitably meshed into discrete cells that can

be uniform or non-uniform.

2. Define Boundary conditions. For transient

problems, the next step is to assign the initial

conditions.

3. After beginning the simulations, the equations

are solved in iterations, either as steady-state or

transient.

4. The ultimate step is to use a postprocessor for

the analysis and visualization of the obtained

(3)

15

5.2.MESHING OF SLURRY IMPELLER

ASSEMBLY:

In Computational Fluid Dynamics, meshing is a

discrete representation of the geometry involved in

the case. Essentially, it assigns cells or smaller

regions over which the solution is obtained. Several

parts of the mesh are grouped into regions where

boundary conditions may be applied to solve the

problem. Moreover, the uses of meshing are not

limited to computational fluid dynamics. Also,

meshing can be used to solve partial differential

equations using Numerical Techniques.

5.3. GRID GENERATION

Using ICEM CFD, the grid for the 3-D model was

created. Care was taken in distribution of grid

elements in the model, because of the size and

complexity of the impeller. Considering the

geometric complexity, unstructured grid which

consists of tetrahedral and triangular element with

ICEM CFD scheme was used.

5.4. BOUNDARY CONDITIONS AND

TURBULENCE MODELS

The simulations were carried out over a six

different operating points with two different

turbulence models namely renormalization group

(RNG) k-ε model and shear stress transport (SST)

k- ε model. Mass flow rate corresponding to

different operating points were specified at the

suction of impeller while total pressure was defined

at the casing outlet

Table 3 Boundary condition

Parameters CFD

Fluid used for simulation Water at 25°C

Pressure at Inlet Pressure = 0 Pa

Total Pressure at Outlet 328438.85 Pa

Density of Fluid 1000 Kg/m3

Viscosity 1.0031e-3 kg/m-s

Turbulence Model K-ε , RNG Model

RPM range 1000 to 1500

5.5. CONVERGENCE CRITERIA

The residual of mass flow rate between inlet and

outlet should be kept at e-5 (5th decimal accuracy)

as shown in Figure 2.

Figure 2 Convergence monitoring

Table 4: Mesh count

Case Study

Surface Mesh Count

Volume Mesh count

Q - CFD at BEP Lps

Case 1 1,15,624 8,23,175 9.77

Case 2 1,91,645 14,64,522 9.32 Case 3 3,32,579 16,00,292 9.25 Case 4 4,31,462 20,22,124 9.19 Case 5 4,89,513 26,23,489 9.20 Case 6 5,11,336 29,46,178 9.20

Mesh count is a significant variable which the CFD

results rely on. Mesh count ranges from 8 lakh

tetrahedrons to around 29 lakh tetrahedrons

(4)

16

6. RESULTS AND CONCLUSIONS

6.1.VELOCITY MAGNITUTE VALUES

6.1.1. K-Epsilon RNG model results

In this functions of the velocity magnitude values

variation is uniform at rated discharge 1035rpm and

1150rpm ,1265 rpm are compared in Kepsilon

-realizable functional equation to apply equation

form analysis based analyzed model but

comparatively non-uniform at other operating

conditions. single Plane and single radial gap are

attached of casing for different operating

conditions. Shows the velocity variation in the

central pressure acting in the different parts.

Fig 3 contour plot Velocity contour 1035 RPM

Above figure 3 this functionally flow equation in

K-Epsilon turbulence model analyzed in rotational

wall functions based to take a result to be done in

static pressure - initialization operating conditions

are 1035 rpm. Results achieved in maximum values

accrue velocity 1.80e+01 m/s

Fig 5 Contour plot Velocity contour 1265 RPM

accrue velocity 2.31e+05 m/s.

6.1.2. K-EPSILON STANDARD

MODEL RESULTS

In this functions of the velocity magnitude values

variation is uniform at rated discharge 1035rpm and

1150rpm ,1265 rpm are compared in Kepsilon

-realizable functional equation to apply equation

form analysis based analyzed model but

comparatively non-uniform at other operating

conditions. Single Plane and single radial gap are

(5)

17 conditions. Shows the velocity variation in the

central pressure acting in the different parts.

Table 5 Velocity Magnitude Comparison

Sl.

No. RPM

K-EPSILON

RNG MODEL

K-EPSILON STANDARD

MODEL

1 1035 1.8e+01 1.8e+07

2 1150 3.0e+07 2.10e+02

3 1265 2.31e+05 2.31e+01

7. CONCLUSION

Based on the numerical analysis of CFD for slurry

impeller the following results are achieved they are

1. Out of various mesh counts 20, 22, 124

elements was found to be optimum.

2. K- ε minimum deviation from the

(6)

18 3. Second order discretization scheme with

simple algorithm for velocity contours hold

good for this analysis.

The flow through a slurry impeller was analyzed

using commercial CFD package FLUENT for

which model test results were available. The

simulations were carried out at six different

operating points between 10% to 20% radial gab

different discharge, to cover the wide range of

operation, with two different turbulence models.

The following conclusions were drawn from the

analysis:

 A Reynolds-averaged Navier- Stokes code with a

two equation turbulence model is able to predict the

important flow physics in a slurry impeller.

 It was found that k-ε SST turbulence model

provides better results compared to RNG k- £

 The selection of speed ranges to simulate in

different flow study equations basis to following this

method.

 It was found that speed range 1035 rpm k- ε SST

turbulence model provides better results compared to

k- ε RNG model. Dynamically apply the overhead

pressure are flowed.

 It was found that speed range 1265 rpm K- ε

RNG turbulence model provides better results

compared to k- ε SST model. Dynamically apply the

overhead pressure are flowed in higher velocity.

 It was found that speed range 1150 rpm K- ε

RNG turbulence model provides better results

compared to k- ε SST model. Dynamically apply the

overhead pressure are flowed in higher velocity.

 The given operating condition slurry impeller

which executes maximum velocity value at 1150 rpm.

REFERENCES

1. Muggli F.A., Eisele K., Casey M.V., Gulich J., Schachenmann A., 1997. Flow analysis in a pump diffuser-part2: validation and limitations of cfd for diffuser flows, Journal of Fluids Engineering, 119, 978-984.

2. Patel K. and Ramakrishnan N., CFD analysis of mixed flow pump. Spence R., Teixeira J.A., 2009. A CFD parametric study of geometrical variations on the pressure pulsations and performance characteristics of a centrifugal pump. Computers & Fluids, 38, 1243–1257. 3. Combès, J.F., "Test Case U3: Centrifugal Pump

with a Vaned Diffuser", ERCOFTAC Seminar and Workshop on Turbo machinery Flow PredictionVII, Aussois, Jan 4-7 , 1999.

4. Ubaldi, M., Zunino, P., Barigozzi, G. and Cattanei, A., "LDV Investigation of the Rotor-Stator Aerodynamic Interaction in a Centrifugal Turbomachine", 8th International Symposium on Applications of Laser Techniques to Fluid Mechanics, Lisbon, 1996.

5. Canepa, E., Cattenei, A., Ubaldi, M. and Zunino, P., "Wake-boundary layer interaction on the vaned diffuser of a centrifugal state", Proc. IMechE, vol. 219, Part A: J. Power and Energy, 401-411, 2005.

6. Bert, P.F., "Modélisation des écoulements instationnaires dans les turbomachines par une méthode éléments finis", Doctoral Thesis, Institut National Polytechnique de Grenoble, 1996.

7. Bert, P.F., Combès, J.F. and Kueny, J.L., "Unsteady Flow Calculation in a Centrifugal Pump Using a Finite Element Method", Proceedings of the XVIII IAHR Symposium on Hydraulic Machinery and Cavitation, 371-380, 1996.

8. Torbergsen, E. and White, M.F., "Transient Simulation of Impeller/Diffuser Interactions", Proceedings of the 1997 ASME Fluids Eng Division Summer Meeting, FEDSM97-3453, 1997.

9. He, L. and Sato, K., "Numerical Solution of

Incompressible Unsteady Flows in

Turbomachinery", Proceedings of the 3rd

ASME/JSME Joint Fluids Eng Conf,

(7)

19 10.Prashant Bhatt, Rajesh Satankar, '

Computational Fluid Dynamics analysis of wind turbine rotor blades- A review', IJCRR, 4(21).

11.Ban,J.O, Lee,U.S, Ahn, B.H, Kin,Y.S, 'Application of Computational Fluid Dynamics to Rotary Compressor Efficiency and Noise', International Compressor Engineering Conference.