ADVANCES in NATURAL and APPLIED SCIENCES ISSN: 1995-0772 Published BYAENSI Publication EISSN: 1998-1090 http://www.aensiweb.com/anas 2017 May 11(7): pages 126-131 Open Access Journal Computational Analysis Of Ducted Fan For Unmanned Aerial Vehicle 1 V. Rajashree, 1 L.Hariramakrishnan, 2 R.Ajithkumar, 3 M.Muneeswaran, 4 P.Saradha 1 Assistant Professor, 2,3,4 UG Scholar Department of Aeronautical Engineering, SNS College of Technology, Coimbatore-641035 Received 28 Feb 2017; Accepted 14 May 2017; Available online 19 May 2017 Address For Correspondence: V. Rajashree, Assistant Professor, 2,3,4UG Scholar Department of Aeronautical Engineering, SNS College of Technology, Coimbatore-641035 E-mail: rajashree.aero@gmail.com Copyright 2017 by authors and American-Eurasian Network for ScientificInformation (AENSI Publication). This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ ABSTRACT The aim of this paper is to analyze incompressible mean flow field around the ducted fan for Unmanned Aerial Vehicle using Computational Fluid Dynamics (CFD). The specific computational system solves the Reynolds-Averaged Navier-Stokes (RANS) equations using an element based finite volume method in the ducted fan rotor. The mass, momentum and energy equations are simultaneously solved over an unstructured finite volume based mesh system. To start with, the duct has been designed and its performance calculations at varying speed and Angle of Attack (AOA) are analyzed. Consequently, prediction of propeller performance for a ducted fan model is calculated and their flow field properties are studied.finally, both the duct and the propeller are coupled together and their corresponding aerodynamic flow calculations have been discussed. KEYWORDS: Navier Stokes equation, ducted fan, rotor, Angle of Attack. INTRODUCTION UAV is the abbreviation of Unmanned Aerial Vehicle which has been in existence since tens of years ago. Compared with manned aircraft UAV has the same ability as robotic aircraft that are computerized and autonomous without an on-board pilot by using a digital and electronic system, thus there is no risk of loss of life and is easier to maintain than manned aircraft. With the development of technology and requirements of industry, UAVs have matured enough for widespread use as they can be remote controlled or autonomously complete missions, not only in civil roles, but also in military operations such as reconnaissance for firefighting and natural disaster, suspect monitoring and strategy attack. There are three primary functions of a fan duct. The first and foremost will be to provide safetyfor the personnel handling the UAV by preventing any physical contact betweenthe human and the propeller rotating at high speed. Other than that, the duct also serves to protect other parts of the aircraft structure. For instance, in the event that the UAV lose control and crash to the ground, the fan duct can absorb most of the impact and protect the propeller blade from damage. At the same time, the fan duct also helps to prevent the spinning propeller from damaging other part of the aircraft structure. Secondly, the inclusion of fan duct into the propulsion system may aids in reducing the noise produced from the propeller. This can be useful especially in commercial aircraft industry whereby noise level have to be kept below certain limit. Nevertheless, as noise is not the primary concern for this project, it is not considered as one of the main design factor. The third function of fan duct is to provide thrust augmentation for the propulsion system. There are 4 principal parameters that determine the effectiveness of the duct in thrust augmentation.these include: (1) Blade ToCite ThisArticle: V. Rajashree, L. Hariramakrishnan, R. Ajithkumar, M. Muneeswaran, P. Saradha., Computational Analysis Of Ducted Fan For Unmanned Aerial Vehicle. Advances in Natural and Applied Sciences. 11(7); Pages: 126-131
127 V. Rajashree et al., 2017/Advances in Natural and Applied Sciences. 11(7) May 2017, Pages: 126-131 Tip Clearance (2) Inlet Lip Radius (3) Diffuser Angle (4) Diffuser Length, which are defined as shown in the Figure 1 Fig. 1: Principal duct parameters affecting shrouded-rotor performance Diffuser angle (θ d), diffuser length (L d), inlet lip radius (r lip) and blade tip clearance (δ tip), throat diameter (D t) II. Propeller Physics: For an open propeller configuration (Fig 2), flow passing through the propeller (slipstream) may experience natural contraction, causing an increase in the far wake velocity, which translates to additional power losses. A. Diffuser angle & Diffuser Section: Diffuser section of the fan duct helps to reduce this power loss by restraining the contraction of the slipstream (Fig 2). Theoretically, the expansion ratio (which depends on both diffuser angle and length) can be increased without limit to attain maximum performance benefit. However, in practical, the performance benefit ceases to grow at some point when the flow can no longer withstand the adverse pressure gradient in the diffuser and start to separate. Fig. 2: An open propeller with slipstream contraction & Ducted propeller with diffuser section B. Blade Tip Clearance: Blade tip clearance refers to the tiny gap between the duct wall and the tip of the propeller blade. It is best to keep the tip clearance as small as possible in order to minimize the tip vortex effect (which may lead to undesirable flow separation and extra drag) C. Inlet Lip Radius: The circular inlet lip of the duct aids in delaying flow separation as it allows the flow to turn in more easily. The larger the inlet lip radius, the better the effect in delaying flow separation. However, the benefit comes with penalties such as increased size and weight, as well as increased skin friction drag. III. Mathematical Formulation: The equations governing the fluid motion are the three fundamental principles of mass, momentum, and energy conservation. Continuity Equation p +. (ρv) = 0 t Momentum Equation ρ DV Dt =. τ ij Energy Equation
128 V. Rajashree et al., 2017/Advances in Natural and Applied Sciences. 11(7) May 2017, Pages: 126-131 ρ De Q + p(. v) = Dt t q + Where P is the fluid density, V is fluid velocity vector, F is the body forces, e is the internal energy, Q is the heat source term, t is time, is the dissipation term, and. q is the heat loss by conduction. Fourier s law for heat transfer by conduction can be used to describe q. q = k T Where k is the coefficient of thermal conductivity, and T is temperature. Depending on the nature of physics governing the fluid motion one or more terms might me negligible. Presence of each term and their combination determines the appropriate solution algorithm and the numerical procedure. IV. Boundary Conditions: The governing equation of fluid motion may result in a solution when the boundary conditions and the initial conditions of specified. The form of boundary conditions that is required by any partial differential equation depends on the equation itself and the way that it has been discretized. Common boundary conditions are classified either in terms of the numerical value that have to be set or in terms of the physical type of boundary condition. For steady stated problems three types of spatial boundary conditions that can be specified i) Dirichlet boundary condition = f(x, y, z) ii) Newman Boundary Condition n = f 2(x, y, z) iii) Mixed Type Boundary Condition a + b n = f 3(x, y, z) IV. Principle Design Characteristics: Table 1: Characteristic design Parameters Chord 0.4167 ft Lift Curve Slope 4.712 /rad Min Lift Coefficient -1.1 Max Lift Coefficient 1.1 Drag Coefficient Gain 0.9 Drag Coefficient Offset 0.9 Duct Moment Coefficient 0.8 V. Design Consideration: Symmetrical section of duct considered and domain created around it with following dimensions. Fig 4 represents Semicircular domain around duct. Upstream distance Downstream distance Height of domain 3 x Diameter of duct 7 x Diameter of duct 3 x Diameter of duct Fig. 3: Duct Model
129 V. Rajashree et al., 2017/Advances in Natural and Applied Sciences. 11(7) May 2017, Pages: 126-131 Fig. 4: Duct with semi circular domain Fig. 5: Propeller without duct Fig. 6: Propeller with duct VI Mesh Creation: Unstructured mesh type is used for the duct i.e. Tetra and Prism mesh. Tetra mesh is used around the entire duct and Prism mesh is used near the duct to capture boundary layer. Table 2: Mesh details Mesh type Hybrid mesh (tetra/prism) Global element size 0.04 Prism mesh 0.004 Prism mesh layers around duct 6 Total mesh elements 5,48,446 Mesh nodes 95,317 Fig. 7: Domain with mesh generated
130 V. Rajashree et al., 2017/Advances in Natural and Applied Sciences. 11(7) May 2017, Pages: 126-131 Fig. 8: Mesh around Moving reference frame VII Result Analysis: After a finite element model has been prepared and checked, boundary conditions have been applied, and the model has been solved, it is time to investigate the results of the analysis. This activity is known as the postprocessing phase of the finite element method. Fig. 9: Lift and Drag coefficients of Propeller Fig. 10: Lift coefficient for ducted Propeller Fig. 11: Drag Coefficient for ducted Propeller
131 V. Rajashree et al., 2017/Advances in Natural and Applied Sciences. 11(7) May 2017, Pages: 126-131 Conclusion: L/D ratio: From the Lift and Drag coefficients plots following results are generated. Table 3: Result Analysis L/D ratio for duct 3.686 L/D ratio for ducted propeller 3.862 Velocity and Pressure Variation: The velocity gradually increases after the propeller blade. The pressure is constant upto the propeller and it suddenly raises at propeller and it settle down at the downstream REFERENCES 1. Andy Ko, Osgar John Ohanian, and Paul Gelhausen, 2007. Ducted Fan UAV Modelingand Simulation in Preliminary Design, AIAA Modeling and Simulation Technologies Conference and Exhibit, South Carolina, 2. Brian L. Stevens and Frank L. Lewis, 1992. Aircraft Control and Simulation. John WileySons Inc., New York. 3. Chester H. Wolowicz and Roxanah B. Yancey, 1972. Longitudinal Aerodynamic of Light, Twin-Engine, Propeller-Driven Airplanes. NASA, Washington, Tech. Rep TN D-680, 4. Hoak, D.E. et al., USAF Stability and Control DATCOM (1965)Douglas Aircraft Company, Inc., Ohio, Tech. Rep for Contract AF 33(616)-6460 & AF 33(615)-1605. 5. Eric, N., Johnson*and Michael A. Turbe 2005. Modeling, Control, and Flight Testing of a Small Ducted Fan Aircraft Georgia Institute of Technology, Atlanta, GA, 30332. 6. Hui-Wen Zhao, 2009. Development of A Dynamic Model of Ducted Fan VTOL UAV. Master thesis, RMIT University, Australia. 7. Herman, S. Fletcher, 1957. Experimental Investigation of Lift, Drag, and Pitching Moment of Five Annular Airfoils. NACA, Washington, Tech. Rep., pp: 4117. 8. Iain K. Peddle, 2005. Autonomous Flight of a Model Aircraft. Master thesis,university of Stellenbosch,South Africa.