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A Parametric Study of the Effect of the Leading- Edge Tubercles Geometry on the Performance of Aeronautic Propeller Using Computational Fluid Dynamics (CFD)

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A Parametric Study of the Effect of the Leading- Edge Tubercles Geometry on the Performance of Aeronautic Propeller Using Computational Fluid Dynamics (CFD) Proceedings of the World Congress on Engineering 2018 Vol II WCE 2018, July 4-6, 2018, London, U.K. A Parametric Study of the Effect of the Leading- Edge Tubercles Geometry on the Performance of Aeronautic Propeller using Computational Fluid Dynamics (CFD) Fahad Rafi Butt, and Tariq Talha Index Terms—amplitude, counter-rotating chord-wise Abstract— Several researchers have highlighted the fact that vortex, flow separation, span-wise flow, tubercle, wavelength the leading-edge tubercles on the humpback whale flippers enhances its maneuverability. Encouraging results obtained due to implementation of the leading-edge tubercles on wings as I. INTRODUCTION well as wind and tidal turbine blades and the fact that a limited research has been conducted related to the implementation of N this study effect of leading-edge tubercle geometry on leading-edge tubercles onto the aeronautic propeller blades was I propeller efficiency over wide range of flight speeds and the motivation for the present study. A propeller that spins rotational velocities was analyzed. Tubercles are round efficiently through air would directly result in environmental bumps that change the aerodynamics of a lift producing friendly flights. Small sized aeronautic propeller; an 8x3.8 body, such as aeronautic wings [1]-[11], wind and tidal propeller, was considered for the present study. As a part of turbine blades [12]-[13] and marine propellers [14] by this study, numerical simulations were carried out to explore the effect of leading-edge tubercle geometry on propeller delaying flow separation. The tubercles also act as a wing efficiency. The tubercle geometry was varied systematically by fence reducing both the span-wise flow and wing tip vortices changing the tubercle amplitude and wavelength. The propeller [1], [4], [7], [12]. performance was analyzed at a wide range of flight speeds and rotational velocities. The results predict an increase in efficiency of the propellers with leading-edge tubercles in comparison with the baseline propeller i.e. the propeller without leading-edge tubercles, while operating at various rotational velocities and flight speeds. A change in the flow- field was observed around the propellers with tubercles at the leading-edge of the propeller blades. It was noted that the addition of the leading-edge tubercles to the propeller geometry delayed flow separation, reduced span-wise flow and the size and strength of the propeller blade tip vortices, leading to a reduced torque requirement from the power source. This lead to an increase in the efficiency of the propellers with leading- edge tubercles. Amongst the various configurations of the tubercle amplitude and wavelength considered for the present study, it was found that the configurations with relatively larger tubercle amplitude and smaller tubercle wavelength, i.e. large tubercle amplitude-to-wavelength ratio, were more efficient. As the advance ratio increased, the increase in efficiency of the propellers with leading-edge tubercles also Fig. 1. Leading-edge protrusions creating chord-wise vortices (marked by improved in comparison with the baseline propeller. An blue arrows) in the x-z plane. increased thrust-to-torque ratio of the modified propeller will have a positive impact on the aircraft’s maximum rate of climb, These vortices are distinctive from the vortices generated time to climb, absolute and service ceilings, range and endurance leading to greener and cost-effective flights. by the conventional vortex generators because they rotate around the axis that is perpendicular to that of the oncoming flow and are observed to be in the plane parallel to the surface of the lifting surface. The strength of these vortices Manuscript received March 03, 2018; revised March 03, 2018. increases with an increase in the angle of attack and the Fahad Rafi Butt, master’s candidate, is with the College of Electrical tubercle amplitude and a decrease in the tubercle wavelength and Mechanical Engineering, National University of Sciences and [2], [7]-[10], [12]. Few relevant studies conducted on Technology, Islamabad, Punjab 46000 Pakistan (phone: 92-300-2631665; e-mail: [email protected]). aeronautic wings, marine propellers, wind and tidal turbine Dr. Tariq Talha, Assistant Professor, is with the College of Electrical blades are discussed in the following paragraphs. and Mechanical Engineering, National University of Sciences and A numerical analysis was performed over a wing section Technology, Islamabad, Punjab 46000 Pakistan (phone: 92-332-6183900; e-mail: [email protected]). using a panel method code by [1]. It was observed that the ISBN: 978-988-14048-9-3 WCE 2018 ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online) Proceedings of the World Congress on Engineering 2018 Vol II WCE 2018, July 4-6, 2018, London, U.K. addition of the tubercles to leading edge of the wing optimized numerically. The tubercle with largest amplitude geometry not only increased the lift coefficient but also and smaller wavelengths was the most efficient in terms of reduced the drag coefficient. At lower angles of attack, the lift-to-drag ratio. The configuration with the leading-edge modified wing, the wing with the leading edge tubercles, had tubercles applied to one-quarter of the blade span was the no penalty in terms of lift-to-drag ratio. It was also observed most efficient, as noted by the wind tunnel experiments. A that the leading-edge tubercles reduced wing tip vorticity. significant increase in the lift-to-drag ratio of the blade Optimization for the tubercle amplitude and wavelength at having leading-edge tubercles was reported for all various angles of attack were conducted by [2], both configurations studied. Moreover, the strong tip vortex numerically and experimentally on an aeronautic wing. The caused by the well-known end effect was also found to be optimum configuration in terms of superior aerodynamic dramatically reduced by the application of the tubercles, as performance was found to be the one with the smaller was also reported by [1]. tubercle wavelength and a larger tubercle amplitude. It was Reference [13] numerically investigated flow over a also found that the modified wing stalled gradually as NREL Phase VI wind turbine with the leading-edge compared to the baseline wing as reported by [4], [7]. A tubercles for various configurations of tubercle amplitudes greater effect on the lift-to-drag ratio of the modified wing and wavelengths. An increased shaft torque was found for all was observed for a change in the tubercle amplitude as the cases at higher wind speeds. It was also concluded that compared to the change in the tubercle wavelength. transient effects were minimal. Low Reynolds number flow over a scalloped flipper with Reference [14] performed steady-state simulations on a leading-edge tubercles was investigated numerically by [4]. marine propeller with leading-edge tubercles. The tubercle The study confirmed the existence of the chord-wise vortices wavelength and amplitude were kept at a 25% and 2.5% of behind the tubercle troughs as reported by [1]. It was found the mean blade chord length for the modified blade. There that the vortices created by the addition of leading-edge results indicated a small increase in the thrust co-efficient. tubercles to the flipper reduced the span-wise flow and the The propeller efficiency increased only at higher advance presence of counter rotating chord-wise vortices increased ratios. the boundary layer momentum leading to delayed stall in the flipper with leading-edge tubercles. Wind tunnel experiments on humpback whale flipper II. NUMERICAL METHODOLOGY models by [7] resulted in an increase in the lift-to-drag ratio of the modified flipper in comparison with the baseline A. Geometric Models and Simulation Methodology flipper for a wide range of angles of attack. Analogous to the An 8x3.8 propeller was modelled and modified1 using the vortex generators over a lifting surface, the tubercles were SolidWorks CAD package and examined as part of the also found increase the stall angle of attack. present study, as shown in Fig. 2. The access to the Reference [9] performed an experimental investigation on geometrical and experimental data [16] necessary for the two distinct NACA airfoils with different aerodynamic verification and validation of the numerical methodology characteristics. The study concluded that the tubercles act in justified the use of a fixed pitch propeller in the present a manner similar to conventional vortex generators and the study instead of a variable pitch propeller. The baseline influence of tubercles on the efficiency of a lifting surface propeller geometries used by [16] were employed. All of the depends not only on the tubercle geometry, controlled by the numerical simulations were performed to predict the three- tubercle amplitude and wavelength, but also on the airfoil dimensional steady–state flow over aeronautic propellers cross section employed. The results demonstrated a using commercially available code SolidWorks Flow similarity in the flow patterns when similar amplitude-to- Simulation Premium© [SFS]. The Local rotating region(s) wavelength ratio of the tubercles was employed. No (Averaging) feature within SFS was employed to simulate significant difference of results was found for the laminar the propeller’s rotation in the standard atmospheric and turbulent flow. The performance with larger amplitude conditions. The employment of the commercial code was tubercles was found to be more favorable in post stall merited because the commercial code was able to satisfy all regimes and reducing the tubercle wavelength was reported the necessary boundary conditions. SolidWorks Flow to improve the maximum lift coefficient, stall angle and Simulation Premium© is a [6], [18] CFD tool built-in to the post-stall characteristics, up to a certain wavelength. SolidWorks© CAD package. SFS employs κ-ε turbulence An aerodynamic model was put forward by [10] to model with damping functions as the turbulence model, explain the increase in stall angle in the lifting surfaces with SIMPLE-R as the numerical algorithm.
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