Increase In Maximum Lift Research Articles

Leading-Edge Active Flow Control Enabled by Curved Fluidic Oscillators

A new design of fluidic oscillator, in which the oscillator is curved along its primary flow direction, allows for a sweeping jet to be placed near the leading edge of a wing as an active flow control device. Previous studies of fluidic oscillator applications have shown their promise as an active flow control device by increasing the lift over a wing and preventing flow separation. However, the planar extent of the flat fluidic oscillators creates challenges when trying to optimally implement them in a confined geometry. The application of these new curved oscillators is experimentally investigated on the leading edge of an upswept NACA0018 airfoil full-span wing. Global load cell measurements of lift, drag, and pitching moment are presented and analyzed using suction surface static pressure taps, and particle image velocimetry data are presented. The effects of active flow control on lift, drag, and stall at a Reynolds number of 100,000 are documented for a variety of oscillator chordwise locations near the leading edge and compared to traditional vortex-generating jets. While further aft-positioned oscillators produced a larger increase in maximum lift, more forward locations resulted in better poststall performance and delayed flow separation over the wing.

Implementation of tubercles on Vertical Axis Wind Turbines (VAWTs): An Aerodynamic Perspective

In recent days, enhancement of Vertical Axis Wind Turbines (VAWTs) by mitigating flow deteriorating effects like dynamic stalling, unsteady wake is given great importance. The following article focuses on implementing four different tubercles on the blades’ leading edge and studying its performance and flow characteristics using CFD techniques. Results indicate that the addition of tubercles generated counter-rotating vortices and delayed flow separation and helped control dynamic stalling. Between azimuth angles 70°–160°, the flow was seen to separate only along the trough regions of the blade and remained attached along the peak regions, thus providing more torque and power. In addition to the enhancements in the flow characteristics, a 28% increase in power coefficient was observed for the optimal configuration at the optimal tip speed ratio. Additionally, a 14% increase in maximum lift generated by the blade was observed. Preliminary aeroacoustics analysis revealed a 12% and 20% decrease in the noise emissions along the blade tip and mid-plane of the turbine, respectively. Hence, it can be shown that tubercles effectively control dynamic stall, reduce noise emissions, and increase the power output of VAWTs.

Transonic small disturbance unsteady potential flow over very high aspect ratio wings

AbstractIn this paper, the prediction of the unsteady flow field over typical high aspect ratio (AR) wings in the transonic flow regime but below the sonic Mach number is of interest. The methodology adopted is a computational approach based on the transonic small disturbance unsteady potential equation. It is shown that the higher AR wings generally have a higher lift coefficient as well as a higher lift-to-drag ratio. With NASA’s common research model (CRM) wing, there is an increase in maximum lift with increasing AR while the induced drag is almost the same. There is also an optimum sweep angle, which is different for each angle-of-attack so that variable sweep lifting surfaces may be designed to provide optimum solutions. The computed flutter speeds indicate an expected reduction with increasing AR.

Design of Thrust-Optimized Scramjet Nozzle and Its Concise Estimation Method

This Paper is a computational investigation of a scramjet nozzle design based on maximum thrust theory and its feasibility analysis. A new design method for a two-dimensional complete thrust-optimized single expansion ramp nozzle under aerodynamic constraints by applying the method of characteristics is proposed. The carefully chosen verification and validation benchmarks confirm the accuracy, effectiveness, and superiority of the current method. Results indicate that the introduced design method has comprehensive advantages over the traditional approach under design/off-design conditions. Specifically, the maximum increase in axial thrust reaches 6.38%, and the maximum increase in lift exceeds 180%. Necessary conditions of the thrust-optimized nozzle design are deduced combining Prandtl–Meyer relation and corner conditions, which provides a direct judgment criterion for the rationality of initial design conditions, and leads to a concise dimension estimation method. Relative errors of no more than 5% demonstrate the credibility of this approach through a comparison with the theoretical solutions. The refined structure topology of the thrust-optimized single expansion ramp nozzle further reveals the equivalent relations between the aerodynamic and geometric design conditions based on the estimation results.

Investigation of self-deploying high-lift effectors applied to membrane wings

ABSTRACTFlow separation followed by aerodynamic stall limits the operation of aircraft. Expanding the flight envelope of aircraft has been a goal of aerodynamicists for decades. This work presents findings from tests in the Oregon State University wind tunnel investigating the effectiveness of a passively actuated suction-surface flap on membrane wings. Experiments were conducted on a rigid plate and membrane wings with and without a pop-up flap. All wings had an aspect ratio of 2, while membrane pre-strain and Reynolds number were varied. An increase in lift at stall was observed for all testing conditions with flap deployment. The observed average increase in maximum lift varied from 5% to 15% for different test conditions. The variation in flap effectiveness is compared to membrane pre-strain, Reynolds number, and wing camber. A quadratic relationship between modelled camber and flap effectiveness is observed, and an optimal level of membrane camber is found to maximise flap effectiveness.

Local correlations for flap gap oscillatory blowing active flow control technology

Active technology for oscillatory blowing in the flap gap has been tested at INCAS subsonic wind tunnel in order to evaluate this technology for usage in high lift systems with active flow control. The main goal for this investigation was to validate TRL level 4 for this technology and to extend towards flight testing. CFD analysis was performed in order to identify local correlations with experimental data and to better formulate a design criteria so that a maximum increase in lift is possible under given geometrical constraints. Reference to a proposed metric for noise evaluation is also given. This includes basic 2D flow cases and also 2.5D configurations. In 2.5D test cases this work has been extended so that the proposed system may be selected as a mature technology in the JTI Clean Sky, Smart Fixed Wing Aircraft ITD. Complex post-processing of the experimental and CFD data was mainly oriented towards system efficiency and TRL evaluation for this active technology.

Reynolds Number Scaling Effects on the European High-Lift Configurations

Within the European High-Lift projects I and II, extensive experimental and numerical investigations on the aerodynamics of high-lift configurations have been carried out. The studies are conducted using the KH3Y windtunnel model DLR F11, which is representative of a wide-body commercial aircraft. A step-by-step complexity increase up to a complete high-lift configuration, including pylon, nacelle, and nacelle strake, is carried out to identify and separate the lift and drag behavior for the components of the high-lift system and their Reynolds number dependency. The wind-tunnel data have been gathered in the European Transonic Wind Tunnel in Cologne in three different test campaigns. To include the complete analysis of the stall behavior for the different configurations of a complex three-dimensional tapered high-lift wing with nacelles extends the scope of a single paper. Therefore, the focus of the present contribution is laid on the detailed analysis of Reynolds number scaling effects with respect to lift curves and drag polars. The combined variation of the dynamic pressure and the total temperature in the European Transonic Wind Tunnel allows covering a Reynolds number range from Re = 1,5 mil. up to deep cryogenic conditions with Re = 25 mil.. The final comparison of the four configurations reveals that the sequence of maximum lift values is maintained for the lowest and highest Reynolds number, although the increments between the configurations differ. The strongest increase in maximum lift is observed up to Re = 5 mil.. In the intermediate range, 5 mil. < Re < 15 mil, a highly nonlinear behavior of the maximum-lift values is observed, which requires further investigation.

Modification of the NACA 632-415 Leading Edge for Better Aerodynamic Performance

Double stall causes more than one power level when stall-regulated wind turbines operate in stall. This involves significant uncertainty on power production and loads. To avoid double stall, a new leading edge was designed for the NACA 632-415 airfoil, an airfoil that is often used in the tip region of wind turbines. A numerical optimization tool incorporating XFOIL was used with a special formulation for the airfoil leading edge shape. The EllipSys2D CFD code was used to analyze the modified airfoil. In theory and in wind tunnel tests, the modified airfoil showed smooth and stable stall characteristics with no tendency to double stall. Also, both theory and wind tunnel tests showed that the overall aerodynamic characteristics were similar to NACA 632-415 except for an increase in the lift-drag ratio below maximum lift and an increase in maximum lift. The wind tunnel tests showed that dynamic stall and aerodynamic damping characteristics for the modified airfoil and the NACA 632-415 airfoil were the same. The modified airfoil with leading edge roughness in general had better characteristics compared with the NACA 632-415 airfoil.

The Development of High Lift, Single-Component Airfoil Sections

SummaryThis paper investigates the possibility of increasing the maximum lift of a single element wing section by the introduction of camber near the trailing edge. The optimum upper surface velocity distribution consists of a constant high velocity “rooftop” over the forward part of the wing section followed by transition and an optimised turbulent boundary layer recovery region to the trailing edge. The height of the rooftop, which essentially determines the maximum lift coefficient, is limited by the amount of recovery attainable without separation of the turbulent boundary layer. An increase in the upper surface velocity at the trailing edge would allow the whole top surface velocity distribution to be raised resulting in a considerable increase in maximum lift. The introduction of camber over the rear part of the wing section should produce the required increase in trailing edge velocity on the upper surface. The practical possibilities of using this technique for increased maximum lift were examined by designing a high lift wing section and testing it in the University of Alberta Low Turbulence Wind Tunnel. The results showed that the new wing section behaved qualitatively as expected. A difference of about 0.5U∞ between upper and lower surface velocities at the trailing edge was achieved, even though the thick boundary layers near the trailing edge tend to reduce the effect of camber. A maximum lift coefficient of 2.64 was measured at a Reynolds number of 1.0 × 106.

Deflected Thrust Effects on a Close-Coupled Canard Configuration

The effects of deflected thrust on the stability and performance of a close-coupled canard fighter configuration are presented. These results were obtained at low speeds in the Langley V/STOL tunnel. Transonic as well as low-speed results are also presented for an unpowered close-coupled canard and a supercruiser configuration. The V/STOL tunnel data indicate an increase in maximum lift and reductions in drag due to lift with the addition of two-dimension al vectored thrust at the wing inboard trailing edge. The longitudinal pitchup associated with the unpowered configuration at higher angles of attack was significantly reduced with power.