INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING AND TECHNOLOGY (IJARET)

INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING AND TECHNOLOGY (IJARET) International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 ISSN 0976-6480 (Print) ISSN 0976-6499 (Online) Volume 3, Issue 1, January- June (2012), pp. 97-106 IAEME: www.iaeme.com/ijaret.html Journal Impact Factor (2011): 0.7315 (Calculated by GISI) www.jifactor.com IJARET I A E M E MODELING AND SIMULATION OF DUCTED AXIAL FAN FOR ONE DIMENSIONAL FLOW Manikandapirapu P.K. 1 Srinivasa G.R. 2 Sudhakar K.G. 3 Madhu D. 4 1 Ph.D Candidate, Mechanical Department, Dayananda Sagar College of Engineering, Bangalore. 2 Professor and Principal Investigator, Dayananda Sagar College of Engineering, Bangalore. 3 Dean (Research and Development), CDGI, Indore, Madhya Pradesh. 4 Professor and Head, Mechanical Department, Government Engg. College, KRPET-571426. ABSTRACT The paper presents to develop the analogy for modeling and simulation of ducted Axial Fan by using the one dimensional flow equation of axial turbo machines. Main objective of this paper is to derive the flow model from radial equilibrium concepts and compute the pressure rise for varying the functional parameters of inlet velocity, whirl velocity, rotor speed and diameter of blade from hub to tip in ducted axial fan by using simulink software for one dimensional flow. In this main phase of paper, the analogies for modeling and simulation has been investigated for optimize the parameter of pressure rise in ducted axial flow fan. Keywords: Pressure rise, Whirl velocity, Pressure Ratio, Flow ratio, Rotor speed, Simulink, Axial Fan. 1.INTRODUCTION Mining fans and cooling tower fans normally employ axial blades and or required to work under adverse environmental conditions. They have to operate in a narrow band of speed and throttle positions in order to give best performance in terms of pressure rise, high efficiency and also stable condition. Since the range in which the fan has to operate under stable condition is very narrow, clear knowledge has to be obtained about the whole range of operating conditions if the fan has to be operated using active adaptive control devices. The performance of axial fan can be graphically represented as shown in figure 1. 97

Fig: 1 Graphical representation of Axial Fan performance curve 2. TEST FACILITY AND INSTRUMENTATION Experimental setup, fabricated to create stall conditions and to introduce unstall conditions in an industrial ducted axial fan is as shown in figure 2. Fig: 2 Ducted Axial Fan Rig A 2 HP Variable frequency 3-phase induction electrical drive is coupled to the electrical motor to derive variable speed ranges. Schematic representation of ducted fan setup is shown in figure 3. 98

Fig: 3 Ducted Axial Fan - Schematic The flow enters the test duct through a bell mouth entry of cubic profile. The bell mouth performs two functions: it provides a smooth undisturbed flow into the duct and also serves the purpose of metering the flow rate. The bell mouth is made of fiber reinforced polyester with a smooth internal finish. The motor is positioned inside a 381 mm diameter x 457 mm length of fan casing. The aspect (L/D) ratio of the casing is 1.2. The hub with blades, set at the required angle is mounted on the extended shaft of the electric motor. The fan hub is made of two identical halves. The surface of the hub is made spherical so that the blade root portion with the same contour could be seated perfectly on this, thus avoiding any gap between these two mating parts. An outlet duct identical in every way with that at inlet is used at the downstream of the fan. A flow throttle is placed at the exit, having sufficient movement to present an exit area greater than that of the duct. 3.0 GOVERNING EQUATION 3.1 Continuity Equation A continuity equation in physics is a differential equation that describes the transport of some kind of conserved quantity. Since mass, energy, momentum, electric charge and other natural quantities are conserved. Continuity equation (3.1) 3.2 Momentum Equation A body of mass m subject to a net force F undergoes an acceleration that has the same direction as the force and a magnitude that is directly proportional to the force and inversely proportional to the mass. Alternatively, the total force applied on a body is equal to the time derivative of linear momentum of the body. Momentum equation 99

) +. ) = p+.[μ ( +Δ )]+ ++Δ.,. (3.2) 3.3 Energy Equation Energy may be stored in systems without being present as matter, or as kinetic or electromagnetic energy. The law of conservation of energy is a law of physics. It states that the total amount of energy in an system remains constant over time (is said to be conserved over time). A consequence of this law is that energy can neither be created nor destroyed: it can only be transformed from one state to another Energy equation ) +. +)) =. + (3.3) 4.0 FLOW MODELING FOR ONE DIMENSIONAL FLOW 4.1 Radial Equilibrium Concepts and evaluation Consider a small element of fluid of mass dm as shown in fig.4 and fig.5 of unit depth and subtending an angle dθ at the axis and rotating about the axis with tangential velocity and at radius r. Casing Streamlines dr p+1/2 dp p+dp Mass/Unit depth Velocity = c θ p+1/2 dp = ρrdθdr Hub r p dθ Axis Fig: 4 Radial equilibrium flow through a rotor blade row Fig: 5 A fluid element in radial equilibrium ( C r = 0) The general three dimensional momentum equation of inviscid fluid in a radial direction expressed in a cylindrical coordinate system can be written as follows: =Vr + +Va (4.1) 100

Assuming axisymmetric flow and imposing a zero radial flow velocity, it can be simplified to = (4.2) The equation 4.2 is consider as the governing equation of axial flow fan for 1- Dimensional flow dp = dr (4.3) v = v v = v = = =.. Pressure Rise = p = Pressure Rise = p = (4.4) (4.5) (4.6) (4.7).. (4.8) The aim of the flow modeling is to measure the pressure rise as a function of whirl velocity and rotor speed for different diameter of blade from hub to tip in ducted axial flow fan. In this flow modeling equation helps to optimize the parameter of pressure rise for different whirl velocity in a ducted axial fan. 5.0 SIMULINK Simulink is a software package for modeling, simulating and analyzing dynamic systems. It supports linear and nonlinear systems, modeled in continuous time, sampled time, or a hybrid of the two. For modeling simulink provides a graphical user interface for building models as block diagrams, using click and drag mouse operations. Simulink includes a comprehensive block library of source, sink of linear and nonlinear components and connectors. 5.1 SIMULINK MODEL FOR ONE DIMENSIONAL FLOW The one dimensional flow model is considered for simulation study. The governing parameters of the fan considered are density of the fluid, diameter of blade from hub to tip, inlet velocity, pressure ratio, rotor speed and the effects of variation of 101

these parameters are testified through simulink simulation model. Constant block, gain block, Math function, Sum block, inverse block, and display block are the typical blocks used for simulink mathematical model in one dimensional flow is shown in fig.6. Fig: 6 Simulink Flow Simulation Model for One Dimensional Flow in Ducted Axial Fan 6.0 RESULTS AND DISCUSSION The aim of the flow modeling and simulation is to compute the pressure rise as a function of whirl velocity and rotor speed for different diameter of blade from hub to tip in ducted axial flow fan. Flow modeling and simulation of one dimensional flow helps to optimize the parameter of pressure rise for different whirl velocity in a ducted axial fan. Pressure Raise in N/m 2 35 30 25 20 15 10 5 0 Rotor Speed 3000 Rpm Rotor Speed 3600 Rpm Rotor Speed 3300 Rpm Rotor Speed 2700 Rpm 0.0575 0.072 0.08625 0.115 0.23 Pressure Ratio Fig.7 Pressure Raise Variations for fixed diameter of Blade Rotor at 0.381 m 102

Analysis of one dimensional flow modeling and their governing parameters were made as a function of whirl velocity, diameter of hub from tip to hub and rotor speed for ducted axial fan. The variations in pressure rise for different pressure ratio at a constant diameter of blade of 0.381m is shown in fig.7. Maximum pressure magnitude is found to be 32 N/ m 2 for the pressure ratio of 0.23. Further, it varies from 1 to 10 N/ m 2 when the rotor speed is incremented by 300 rpm. Pressure Raise in N/m 2 8 7 6 5 4 3 2 1 Pressure Ratio 0.115 Pressure Ratio 0.0575 Pressure Ratio 0.08625 Pressure Ratio 0.072 0 2400 2600 2800 3000 3200 3400 3600 Rotor Speed ( Rpm ) Fig.8 Pressure Raise Variations for fixed diameter of Blade Rotor at 0.381 m The variations in pressure rise for different rotor speed from 2400 rpm to 3600 rpm for fixed diameter of blade of 0.381 m is shown in fig.8. Maximum pressure magnitude is found to be 8 N/ m 2 for the pressure ratio of 0.115. Further, it varies from 1 to 5 N/ m 2 when the rotor speed is incremented by 200 rpm. Pressure Raise in N/m 2 250 200 150 100 50 Rotor Speed 3000 Rpm Rotor Speed 3600 Rpm Rotor Speed 2400 Rpm Rotor Speed 2700 Rpm Rotor Speed 3300 Rpm 0 0.0131 0.0714 0.01651 0.381 0.881 2.04 Blade Diameter in m Fig.9 Pressure Raise Variations for fixed Pressure Ratio of 0.115 103

The variations in pressure rise for different diameter of blade from 0.0131m to 2.04 m at a constant pressure ratio of 0.115 is shown in fig.9. Maximum pressure magnitude is found to be 210 N/ m 2 for the blade diameter of 2.04 m. Further, it varies from 0 to 45 N/ m 2 when the rotor speed is incremented by 300 rpm. Pressure Rise in N/m 2 160 140 120 100 80 60 40 20 0 Pressure Ratio 0.115 Pressure Ratio 0.0575 Pressure Ratio 0.08625 Pressure Ratio 0.072 0.0131 0.0714 0.01651 0.381 0.881 2.04 Blade Diameter in m Fig.10 Pressure Raise Variations at constant Rotor Speed of 3000 Rpm The variations in pressure rise for different diameter of blade from 0.0131m to 2.04 m at constant rotor speed of 3000 rpm is shown in fig.10. Maximum pressure magnitude is found to be 160 N/ m 2 for the pressure ratio of 0.115. Further, Pressure magnitude is found to be varying from 0 to 160 N/ m 2 for every double increment of rotor diameter. 7.0 CONCLUSION In this paper, an attempt has been made to develop the flow modeling and simulation for one dimensional flow in ducted axial fan by using theory of radial equilibrium equation. It is useful to design the operating condition of axial fan to measure the parameters of pressure rise as a function of pressure ratio, rotor speed, and diameter of blade from hub to tip in ducted axial fan. Further, this work can be extended by working on the modeling and simulation of characteristic study in stall control. The results so far discussed, indicate that flow modeling and simulation of one dimensional flow in ducted axial fan is very promising. ACKNOWLEDGEMENT The authors gratefully thank AICTE (rps) Grant. for the financial support of present work. 104

NOMENCLATURE c x = Axial velocity in m/s = Whirl velocity in m/s r 2 = Radius of blade tip in m r 1 = Radius of blade hub in m N = Tip speed of the blades in rpm v a = Axial velocity in m/s dp= P 2 - P 1 = Pressure rise in N/m 2 REFERENCES d = Diameter of the blade in m ρ air = Density of air in kg/m 3 v w = Whirl velocity in m/s η = Efficiency of fan [1] Day I J, Active Suppression of Rotating Stall and Surge in Axial Compressors, ASME Journal of Turbo machinery, vol 115, P 40-47, 1993 [2] Patrick B Lawlees, Active Control of Rotating Stall in a Low Speed Centrifugal Compressors, Journal of Propulsion and Power, vol 15, No 1, P 38-44, 1999 [3]C A Poensgen, Rotating Stall in a Single-Stage Axial Compressor, Journal of Turbo machinery, vol.118, P 189-196, 1996 [4] J D Paduano, Modeling for Control of Rotating stall in High Speed Multistage Axial Compressor ASME Journal of Turbo machinery, vol 118, P 1-10, 1996 [5] Chang Sik Kang, Unsteady Pressure Measurements around Rotor of an Axial Flow Fan Under Stable and Unstable Operating Conditions, JSME International Journal, Series B, vol 48, No 1, P 56-64, 2005 [6] A H Epstein, Active Suppression of Aerodynamic instabilities in turbo machines, Journal of Propulsion, vol 5, No 2, P 204-211, 1989 [7] Bram de Jager, Rotating stall and surge control: A survey, IEEE Proceedings of 34th Conference on Decision and control, 1993 [8] S Ramamurthy, Design, Testing and Analysis of Axial Flow Fan, M E Thesis, Mechanical Engineering Dept, Indian Institute of Science, 1975 [9] S L Dixon, Fluid Mechanics and Thermodynamics of Turbo machinery, 5th edition, Pergamon, Oxford, 1998 [10] William W Peng, Fundamentals of Turbo machinery, John Wiley & sons.inc, 2008 AUTHORS Manikandapirapu P.K. received his B.E degree from Mepco Schlenk Engineering college, M.Tech from P.S.G College of Technology,Anna University,and now is pursuing Ph.D degree in Dayananda Sagar College of Engineering, Bangalore under VTU University. His Research interest include: Turbomachinery, fluid mechanics, Heat transfer and CFD. 105

Srinivasa G.R. received his Ph.D degree from Indian Institute of Science, Bangalore. He is currently working as a professor in mechanical engineering department, Dayananda Sagar College of Engineering, Bangalore. His Research interest include: Turbomachinery, Aerodynamics, Fluid Mechanics, Gas turbines and Heat transfer. Sudhakar K.G received his Ph.D degree from Indian Institute of Science, Bangalore. He is currently working as a Dean (Research and Development) in CDGI, Indore, Madhyapradesh. His Research interest include: Surface Engineering, Metallurgy, Composite Materials, MEMS and Foundry Technology. Madhu D received his Ph.D degree from Indian Institute of Technology (New Delhi). He is currently working as a Professor and Head in Government Engineering college, KRPET-571426, Karnataka. His Research interest include: Refrigeration and Air Conditioning, Advanced Heat Transfer Studies, Multi phase flow and IC Engines. 106