Increase In Maximum Lift Coefficient Research Articles

Circulation-controlled wind-assisted ship propulsion: Technical innovations for future shipping industry decarbonization

Amidst mandatory policies aimed at energy savings and emission reductions in the shipping industry, wind-assisted ship propulsion technology has gained prominence for its immediate practicality in promoting environmental sustainability. Wing-sails possess favorable aerodynamic characteristics and adjustable capabilities, yet their efficiency is impeded by flow separation at high angles of attack. This study addressed the challenge of mitigating delayed separation and enhancing lift at large angles of attack for wing-sails through technical solutions involving trailing-edge circulation control and leading-edge boundary layer control. Three-dimensional steady-state flow fields of conventional and circulation-controlled wing-sails were accurately modeled using a Generalized k-ω (GEKO) model across angles of attack ranging from 0° to 30°. Under moderate jet strength conditions with a velocity ratio of 5, the stall angle of attack of the circulation-controlled wing-sail was delayed by approximately 6°. Furthermore, compared to a conventional wing-sail, the circulation-controlled variant exhibited a 111 % increase in maximum lift coefficient and a 120 % rise in maximum resultant force coefficient. The energy-saving and emission reduction benefits of implementing this innovative technology were quantified using the Energy Efficiency Design Index (EEDI) on a real very large crude carrier (VLCC). The circulation-controlled wing-sail demonstrated a 10.38 % reduction in EEDI under optimal operating conditions with medium jet strength, compared to an unassisted vessel. Moreover, this reduction was enhanced by 77.55 % compared to incorporating a conventional wing-sail. These discoveries signify an advancement in wind-assisted ship propulsion technology on an innovative frontier, promising greater energy utilization and reduced fuel consumption, thereby facilitating the achievement of stringent green ship standards.

Design and computational fluid dynamics analysis of bio-inspired non slender cropped delta wingsuit

This study examines the effect of bio-inspired serrations on aerodynamic performance of a Non Slender cropped delta wingsuit model. In this study, Gottingen 228 aerofoil is used for designing the wingsuit model having AR of 1.00 using CAD software Solidworks. Ansys Fluent solver has been utilised to solve the Reynolds Averaged Navier–Stokes (RANS) equations with a k− $$\omega$$ turbulence model. The flow velocity was kept at 45 m/s with Re ~ 2.6 × 106 and angle of attack was varied from 0° to 45°. Computations revealed that the wingsuit with serrations in comparison with clean basemodel had a notable increase in maximum lift coefficient. The results were compared with the experimental and CFD results of existing literature in the open domain. The serrated non slender delta wingsuit performs extremely well giving a lift coefficient of 2.74 and $$C_{{\text{L}}}$$ / $$C_{{\text{D}}}$$ of 9.72. The results were validated by comparing them with flat plate and non slender cropped delta wing results available in the existing literature. A good agreement in terms of trends was obtained for $$C_{{\text{L}}}$$ and $$C_{{\text{D}}}$$ which indicates that proposed wingsuit should perform well aerodynamically under typical wingsuit flying conditions.

Performance of a hydrofoil operating close to a free surface over a range of angles of attack

Performance of a NACA 634-021 hydrofoil in motion under and in close proximity of a free surface for a large range of angles of attack is studied. Lift and drag coefficients of the hydrofoil at different submergence depths are investigated both numerically and experimentally, for 0° ≤ AoA≤30° at a Reynolds number of 105. The results of the numerical study are in good agreement with the experimental results. The agreement confirms the new finding that for a submerged hydrofoil operating at high angles of attack close to a free surface, the interaction between the hydrofoil-motion induced waves on the free surface and the hydrofoil results in mitigation of the flow separation characteristics on the suction side of the foil and delay in stall, and improvement in hydrofoil performance. In comparing with a baseline case, results suggest a 55% increase in maximum lift coefficient and 90% average improvement in performance for, based on the lift-to-drag ratio, but it is also observed significant decrease of lift-to-drag ratio at lower angles of attack. Flow details obtained from combined finite volume and volume of fluid numerical methods provide insight into the underlying enhancement mechanism, involving interaction between the hydrofoil and the free surface.

Effect of Gurney Flap Geometry on a S809 Airfoil

In this paper, the effect of Gurney flap shapes on wind turbine blade airfoil S809 has been studied by numerical simulation. First, the O-type grid is used in the numerical simulation. By comparing with experimental data, such as the lift force, the drag coefficient, and the pressure distribution, the accuracy of the simulation method is validated. Second, the research on the widths of three kinds of rectangular Gurney flaps at the trailing edge of the S809 airfoil is carried out. Rectangular Gurney flaps can considerably increase the lift in both the linear and nonlinear sections, and the maximum lift coefficient can be increased by 20.65%. In addition, the drag and the pitching moment are increased. However, the width of the rectangular Gurney flap has a small impact on the lift, the drag, and the pitching moment. Finally, the effects of rectangular and triangular Gurney flaps on the aerodynamic characteristics of the S809 airfoil are compared. The results show that the triangular flaps can obtain an increase of maximum lift coefficient by 28.42%, which is better than 16.31% of the rectangular flaps.

Improved performance of a slotted blade using a novel slot design

Efficient capture of wind energy requires optimal dynamic performance of turbine blades, desirably including delaying stall to higher angles of attack (AoAs). Stall is associated with flow separation close to the leading edge on the suction side of a blade so that delaying flow separation mitigates this condition. Merits of passive slots in wings for increasing their lift are well known. Typically, however, the increase in lift is accompanied by a corresponding increase in drag so that the overall aerodynamic efficiency is at most marginally improved. Here, we discuss application of a custom optimized-design internal slot on a NACA 634-021 airfoil blade to allow ventilation of flow through the slot from the pressure side to the suction side of the blade, in support of delaying flow separation, and stall. Delaying flow separation, results in increase in lift and decrease in drag at significantly high angles of attack. Slot width and inclined angle were varied to determine the optimum configuration. Dynamic performance of the blade was investigated both numerically and experimentally, with angles of attack in the range 0o≤AoA≤30o at a Reynolds number of 105. Lift and drag coefficients of the slotted airfoils predicted from the computational fluid dynamics (CFD) study correlate well with the corresponding coefficients determined via experiments. Experimental results show that a 58% increase in maximum lift coefficient and an 14% increase in maximum lift-to-drag ratio could be achieved with the optimum design case. Flow details obtained from the CFD study provide better insight into the underlying control mechanism of the internal slot. The findings could have significant implications for aeronautics and for improving capture of renewable energy from wind.

Impact of pulsed jet actuators on aircraft mass and fuel consumption

Pulsed jet actuators (PJAs) are one of the candidate technologies to be integrated in Fowler flaps to increase the maximum lift coefficient of transport aircraft in the landing configuration. The total system consists of the actuators plus sensors, a piping system to supply pressurized air and a (redundant) power and communication system to provide actuator control. In this paper, it is investigated what increase in the maximum lift coefficient is required to justify the added weight and power off-takes that accompany the integration of pulsed jet actuators. This is done by making an automated design process for the overall aircraft, the piping assembly system, and the electrical wiring interconnection system. These last two sub-systems rely on KBE techniques that automate dimensioning and performance evaluation. A test case is specified that encompasses the design of a typical single-aisle mid-range aircraft with and without the PJA system installed. It is concluded that the introduction of the PJA system requires at least an increase in maximum lift coefficient of 0.2 to justify the increase in system mass and power off-takes. Furthermore, it is shown that if the maximum lift coefficient increases with 0.4, only small reductions in maximum take-off weight (−0.3 %) and operating empty weight (−0.6 %) can be expected, while the total fuel burn remains virtually constant.

Roughness and Turbulence Effects on the Aerodynamic Efficiency of a Wind Turbine Blade Section

Numerous experiments were conducted on a section of a 660kw wind turbine blade in a subsonic wind tunnel. The selected airfoil was tested with a clean and distributed contamination roughness surface, also with high and low tunnel turbulence intensity. Surface contamination was simulated by applying 0.5 mm height roughness over the entire upper surface of the airfoil. The surface pressure distribution is measured in the steady and unsteady condition at three Reynolds numbers, 0.43, 0.85, and 1.3 million, and over a range of angles of attack, AOA=7o-19o. Unsteady data were acquired by both pitch and plunge-type oscillation of the model about its quarter chord at a reduced frequency of 0.07. Results show that the surface roughness reduces section aerodynamic efficiency and the lift coefficient, but increases the drag coefficient for all the Reynolds numbers. The application of roughness reduces upper surface pressure coefficient and extends a separation region at high angles of attack. Increasing the tunnel turbulence intensity resulted in delay of the stall, an increase of maximum lift coefficient, and smoothness of the stall behavior. However, the drag coefficient increased significantly. Furthermore, turbulence intensity affected the predicted power output of the blade.

CFD simulation of momentum injection control past a streamlined body

PurposeThe purpose of this paper is to achieve high‐performance aerofoils that enable delayed stall conditions and achieve high lift to drag ratios.Design/methodology/approachThe unsteady Reynolds averaged Navier‐Stokes equations are employed in conjunction with a shear stress transport (κ‐ω) turbulence model. A control equation is designed and implemented to determine the temporal response of the actuator. A rotating element, in the form of an actuator disc, is embedded on the leading edge of NACA 0012 aerofoil, to inject momentum into the wake region. The actuator disc is rotated at different angular speeds, for angles of attack (α) between 00 and 240.FindingsPhenomena such as flow separation, wake vortices, delayed stall, wake control, etc. are numerically investigated by means of streamlines, streaklines, isobars, etc. Streamwise and cross‐stream forces on the aerofoil are obtained. The influence of momentum injection parameter (ξ) on the fluid flow patterns, and hence on the forces acting on the streamlined body are determined. A synchronization‐based coupling scheme is designed and implemented to achieve annihilation of wake vortices. A delayed stall angle resulted with an attendant increase in maximum lift coefficient. Due to delay and/or prevention of separation, drag coefficient is also reduced considerably, resulting in a high‐performance lifting surface.Research limitations/implicationsThe practicality of momentum injection principle requires both wide ranging and intensive further studies to move forward beyond the proof of concept stage.Practical implicationsDetermination of forces and moments on an aerofoil is of vital interest in aero‐dynamic design. Perhaps, runways of the future can be shorter and/or more pay load can be carried by an aircraft, for the same stall speed.Originality/valueThe paper describes how a synchronization‐based coupling scheme is designed and implemented along with the RANS solver. Furthermore, it is tested to verify the dynamic adaptability of the wake vortex annihilation for NACA 0012 aerofoils.

Dielectric Barrier Discharge Flow Control at Very Low Flight Reynolds Numbers

Experiments were performed on a flat-plate airfoil and an Eppler E338 airfoil at very low flight Reynolds numbers (3000 ≤ Re ≤ 50,000), in which dielectric barrier discharge plasma actuators were employed at the airfoil leading edges to effect flow control. The actuators were driven in a high-frequency (kilohertz) steady mode and a pulsed mode in which pulse frequency and duty cycle were varied in a systematic fashion. Optimum reduced frequencies for generating poststall lift were approximately between 0.4 and 1, and this was broadly consistent with zero-mass-flux slot-blowing data acquired at Reynolds numbers that were approximately 200 times higher. Nevertheless, profound differences in the response to reduced frequency and duty cycle were observed between the flat-plate and E338 airfoils. In general, actuation produced considerable performance improvements, including an increase in maximum lift coefficient of 0.4 to 0.8 and maintained elevated endurance at significantly higher lift coefficients. Actuation in the steady mode resulted in circulation control at Re = 3000. Pulsed actuation also exerted a significant effect on the wake at prestall angles of attack, in which control of the upper-surface flat-plate bubble shedding produced significant differences in wake spreading and vortex shedding. The flat plate was also tested in a semispan-wing configuration (AR = 6), and the effect of control was comparable with that observed on the airfoil.

The effect of trailing edge extensions on the performance of the Göttingen 797 and the Wortmann FX 63-137 aerofoil sections at Reynolds numbers between 3 x 105 and 1 x 106

SummaryThe effect of trailing edge extensions was tested for the twodimensional Göttingen 797 and Wortmann FX 63-137 aerofoil sections with smooth surfaces at chord Reynolds numbers from 3 x 105 to 1 x 106 in the 8ft x 6ft low speed wind-tunnel at the Cranfield Institute of Technology. Force measurements were made on the basic aerofoil sections and with extension plates of 10% and 20% chord set tangential to the upper surface at the trailing edge. It was verified that the addition of an extension plate effectively brings about an increase of maximum lift coefficient and an improved lift-to-drag ratio for the Göttingen aerofoil section. However, the effect of the extension plate was small on the Wortmann aerofoil section.