Effect Of Leading Edge Tubercles Research Articles

Effect of leading-edge tubercles on the hydrodynamic characteristics and wake development of tidal turbines

This paper describes an investigation into the effect of leading-edge tubercles on turbine hydrodynamic characteristics and wake development characteristics. The hydrodynamic performance and wake velocity distribution of a modified turbine—termed Bio-turbine—are tested by a channel test. The normalized mean velocity profile obtained by the large eddy simulation (LES) method is consistent with the experimental data, which indicates that the numerical method is credible in predicting turbine performance and wake turbulence. By carefully examining the wake velocity deficit, turbulence intensity variation, and evolution of the vortex structure, it is possible to discuss how the leading-edge tubercles affect turbine performance and wake instability at various tip speed ratios (TSRs). The findings demonstrate that Bio-turbine has superior energy conversion performance at high TSRs, but the power amplitude is larger and the instability is more prominent. Furthermore, the unique structure of the blade leading edge alters the pressure distribution and flow separation behavior of the blade suction side, resulting in an enlargement of the wake recovery area. As a result, greater emphasis should be placed on the design of turbines with leading-edge tubercles.

The effect of leading-edge tubercle on a tapered swept-back SD7032 airfoil at a low Reynolds number

An experimental study is performed to research the effect of the implemented leading-edge tubercles on the tapered swept-back SD7032 airfoil at Re of 5.5 × 104 and 1.1 × 105. In this study, along with a baseline model with no tubercles (T0), in total four different configurations are used for analysis of the aerodynamic characteristics. In the other three models (T1, T2, T3) mainly different amplitude and wavelength modulations are studied. In all experimental studies, force measurements are performed by using a six-axis load cell force measurement device. To achieve detailed information on the flow field of all models, surface oil flow visualization technique is used for visualization purposes at Re = 1.1 × 105. The geometric specifications of the model are the sweep angle of 30⁰, the tip chord of 37.5 mm, the root chord of 112.5 mm, and the span of 300 mm. Airfoil models with the LE tubercles significantly improve lift curve at almost all AoAs as compared to the baseline model. The streamwise vortices are positioned together more closely leading to interaction with each other. Consequently, these interactions lead to an increase in turbulence. This increase in turbulence may lead to a better mixing and increase in momentum exchange in the boundary layer. Amongst the models (T1-T3), the best airfoil model is determined as T3, having a1 = 0.06c, λ1 = 0.5c, a2 = 0.015c, and λ2 = 0.125c parameters, in terms of lift, drag and CL/CD ratios.

Experimental investigation on the effect of Leading Edge Tubercles on the Performance of Marine Propellers in fully wet condition

Leading edge tubercles (LET) is an attractive passive flow control solution that has been proved to enhance the hydrodynamic performance and efficiency of lifting surfaces adopted in many engineering areas. Nonetheless, their industrial application in control and propulsion devices of marine vehicles is still at the beginning. To move further steps ahead, a preliminary experimental campaign for a five bladed Wageningen B-screw propeller modified with three different configurations of leading edge tubercles was carried out in cavitation free conditions. In particular, the propellers were tested in open water conditions in straight and oblique flow at incidences of 10° and 20°, with the aim to study the effects of LET during steady and moderate unsteady conditions. The propellers are tested at two different chord Reynolds numbers in order to investigate their applicability also to small autonomous marine vehicles. The analysis proved that suitable layout of tubercles can enhance the hydrodynamic efficiency in axial symmetric flow while reducing undesired effects caused by operation in off-design.

Numerical Investigation on the Effect of Leading-Edge Tubercles on the Laminar Separation Bubble

The effect of leading-edge tubercles on the aerodynamic performance of E216 airfoil is studied by steady 3D numerical simulations using Transition γ−Reθ turbulance model. The investigation is carried out for the various angles of attack in the pre-stall region at Reynolds number of 100,000. Various tubercle configurations with different combinations of amplitude ranging from 2 mm to 8 mm and wavelength varying from 15.5mm to 62 mm are studied. The effect of tubercle parameters on the laminar separation bubble (LSB) is extensively studied. Improvement in the coefficient of lift (Cl) is observed for most of the tubercled models and is significant at high angles of attack. But the simultaneous increase in the drag coefficient resulted in a marginal improvement in the coefficient of lift to drag ratio (Cl/Cd) for most of the cases except for A2W62, which produced a peak value of 46.91 at AOA 6◦ which is higher than that for the baseline by 7.37%. Compared to the baseline, the magnitude of suction peak is higher along the trough and lower along the peak. The low amplitude and low wavelength tubercle model exhibited smooth surface pressure coefficient (Cp) distribution without any sign of strong LSB formation. The LSB moves upstream with the increase in amplitude and wavelength. The LSB along the trough is formed ahead of that at peak inducing three-dimensional wavy shaped LSB unlike the straight LSB as in baseline. Two pairs of counter rotating vortices are formed on the airfoil surface between the adjacent peaks at two different chord-wise locations which strongly alter the flow pattern over it.

The effects of leading-edge tubercles on dynamic stall

The effects of leading-edge tubercles, based on the flippers of humpback whales, on the flow field around an airfoil undergoing large-amplitude dynamic changes in the angle of attack have been studied experimentally. Airfoils were pitched from an initial angle of attack of to at constant pitch rates with a chord Reynolds number of 12 000. Velocity and vorticity fields around a standard NACA 0012 airfoil and NACA 0012 modified with leading-edge tubercles were quantified using molecular tagging velocimetry. Vortex dynamics were characterized by tracking the location, core radius and circulation. The resulting velocity fields showed that the dynamics of the formation and separation of the leading-edge vortex were fundamentally different between the straight leading-edge airfoil and the tubercled airfoil. The tubercled airfoil also showed spanwise variation in dynamics of the dynamic stall vortex (DSV) formation. The characteristics of the DSV, specifically the circulation and proximity of the DSV to the airfoil suction surface, are known to have an impact on lift during dynamic pitching. The results showed that the DSV was stronger and remained closer to the airfoil longer for the modified airfoil. The baseline DSV convected away from the airfoil faster than the DSV on the tubercled airfoil once it began to separate from the airfoil. Shear-layer vortices, which form during dynamic stall near the mid-cord region, appeared to affect the convective behaviour of the DSV. The results suggest that the leading-edge tubercles observed on Humpback whale flippers act as passive flow-control mechanisms to control or delay dynamic stall.

Investigation of the Effect of Leading Edge Tubercles on Wingsail Performance

Investigation of the Effect of Leading Edge Tubercles on Wingsail Performance

Numerical Investigation of the Effect of Leading-Edge Tubercles on Propeller Performance

The propeller is a fundamental part of an aircraft powered by the turboprops, piston engines, or electric motors. A propeller that spins efficiently through air directly results in environmentally friendly and cost-effective flights. As a part of this novel study, the effect of leading-edge tubercle amplitude and wavelength on propeller efficiency was explored. The effect of leading-edge tubercles on various propeller solidities was also investigated. In addition, the effect of leading-edge tubercles on propeller diameter-to-pitch ratio was also studied for a wide range of advance ratios and rotational velocities. Small-sized aeronautic propellers were considered for the present study. The results predict an increase in efficiency of the modified propellers in comparison with the baseline propellers for all the cases considered in the present study. Therefore, a propeller-driven aircraft with the modified propeller installed in place of the baseline propeller, with an increased thrust-to-torque ratio, will have the potential for a higher maximum rate of climb, lower time to climb, higher absolute and service ceilings, and higher range and endurance, leading to greener and cost-effective flights.

Effects of leading-edge tubercles on wing flutter speeds

The dynamic aeroelastic effects on wings modified with bio-inspired leading-edge (LE) tubercles are examined in this study. We adopt a state-space aeroelastic model via the coupling of unsteady vortex-lattice method and a composite beam to evaluate stability margins as a result of LE tubercles on a generic wing. The unsteady aerodynamics and spanwise mass variations due to LE tubercles have counteracting effects on stability margins with the former having dominant influence. When coupled, flutter speed is observed to be 5% higher, and this is accompanied by close to 6% decrease in reduced frequencies as an indication of lower structural stiffness requirements for wings with LE tubercles. Both tubercle amplitude and wavelength have similar influences over the change in flutter speeds, and such modifications to the LE would have minimal effect on stability margins when concentrated inboard of the wing. Lastly, when used in sweptback wings, LE tubercles are observed to have smaller impacts on stability margins as the sweep angle is increased.