Significant Increase In Lift Research Articles

Wind tunnel experimental study of aerodynamic characteristics of co-flow jet wing with built-in air source

To further investigate the aerodynamic characteristics and control mechanisms of co-flow jet wings, this study presents the design of a co-flow jet wing (CFJ-CLARKY18) with an embedded micro centrifugal compressor. The CFJ-CLARKY18 wing, based on the CLARKY18 airfoil, incorporates a miniature centrifugal compressor positioned horizontally within the wing's cavity, with its rotor axis perpendicular to the wing chord line, thus alleviating geometric constraints and the compressor's exhaust swirl. The integration of the co-flow jet device with the wing is achieved through a split-flow channel design to ensure uniform co-flow jet injection, followed by verification of jet uniformity and calibration of six jet momentum coefficients. Subsequently, static and dynamic control experiments of the co-flow jet wing are conducted in an open-return wind tunnel, utilizing force measurement systems and high-speed particle image velocimetry tools to investigate its aerodynamic characteristics and control mechanisms. Static stall tests indicate that, compared to the original wing, the CFJ-CLARKY18 wing exhibits a significant increase in lift and a noticeable delay in stall angle. At low angles of attack, an increase in co-flow jet momentum leads to a reduction in drag coefficient, with the possibility of achieving negative drag (thrust) even at high co-flow jet momentum coefficients. The results of dynamic stall tests with force measurements indicate that, while keeping the reduced frequency constant, an increase in co-flow jet momentum coefficient results in higher maximum lift and average lift coefficients, accompanied by a significant reduction in average drag coefficient and the hysteresis loop area of the lift coefficient. Despite the increased reduced frequency exacerbating the wing's stall effect, the stall effect weakens significantly once the co-flow jet momentum coefficient is increased.

Aerodynamic Shape Optimization of a NACA0018 Airfoil Using Adjoint Method and Gradient-Based Optimizer

The purpose of this study is to demonstrate the suitability and efficacy of the adjoint method on the aerodynamic shape optimization on a simple symmetrical airfoil NACA0018 at low Reynolds number for wind turbine application. The adjoint method has been used in many pressure-based numerical simulations with various degrees of success leading to optimized geometries in their respective uses. ANSYS Fluent code was used in this simulation. Lift to drag ratio was defined as the observables for which adjoint sensitivities were formulated. The objective function of the optimization was set to maximize the lift to drag ratio of the airfoil by 20%. The optimization regime showed significant increase in lift and drag ratio from the initial baseline NACA0018 value of 0.0211 up to 3.66 for the optimal NACAOpt. The results demonstrate the potential of the adjoint solver paired together with the gradient-based optimizer to improve the geometry for shape optimization in many CFD applications.

Spectral and wavelet analysis in the wake of an airfoil with Gurney flap

In this work we identify the coherent vortices in the leeward wake of an HQ 17 airfoil with a Gurney flap. This high-lift device consists of a small plate perpendicular to the airfoil, at or near the trailing edge, with a height � of the order from 1% to 4% of the chord. The overall effect is to produce a significant increase in lift, together with a relatively minor increase in airfoil drag. Its geometry generates vortex shedding of spatial scale H, which modulates the wake and thus influence the global configuration of the flow. A numerical study was performed with the commercial software ANSYS Fluent. Simultaneously, experiments were carried out in the wind tunnel of the Aeronautical Departmental Area from the Engineering School of the National University of La Plata. With a Dantec StreamLine hot-wire anemometer, records of the instantaneous horizontal and vertical velocity components in the airfoil wake were obtained. Both the experimental data and those obtained by numerical simulation were analyzed with the continuous wavelet transform technique, in order to identify and characterize the coherent vortices in the wake. Results show the shed vortices structure and the organization degree of this periodic shedding.

Optimisation of Trapped Vortex Cavity for Airfoil Separation Control

The effects of a Trapped Vortex Cavity (TVC) on the aerodynamic performance of a NACA 0024 airfoil at a constant angle of attack (AoA) of 14◦ were investigated in this study. It was observed that mass suction (MFR) was required to stabilise the vortex within the cavity segment. Lift to drag ratio (L/D) and MFR were chosen as performance objectives, along with a fully attached flow constraint (flow separation at X/c ≥ 95% ). Parametric analysis was carried on the baseline airfoil with and without suction and compared to the airfoil with TVC with and without suction. It was observed that L/D increases as MFR increases for a baseline airfoil, and flow separation is delayed at high suction values (MFR = 0.2 kg/s). The TVC modifies the pressure distribution on the baseline airfoil when MFR is applied to the cavity section and there is a significant increase in lift; thus, L/D increases and flow separation is delayed. A lower value of MFR = 0.08 kg/s is sufficient to stabilise the vortex and improve the efficiency of the TVC airfoil. The findings of these parametric studies were used to do a multi-objective optimisation using a genetic algorithm to attain the desired cavity shape while achieving the largest L/D and the lowest MFR (that is proportional to the power required for control) with a fully attached flow constraint. It was found that mass suction and cavity shape both had an equal influence on flow control. The Pareto optimal front yielded a series of optimum designs. One of them was subjected to an off-design analysis in order to validate its performance at other incidences. It was observed that it performs better than the baseline airfoil, with an improved L/D and an increase in stall angle from 10◦ to 14◦.

Oscillatory Blowing: A Tool to Delay Boundary-Layer Separation

The effects of oscillatory blowing as a means of delaying separation are discussed. Experiments were carried out on a follow, flapped NACA 01115 airfoil equipped with a two-dimensional slot over the hinge of the flap. The flap extended over 25% of the chord and was detected at angles as high as 40 deg. The steady blowing momentum coefficients could be varied independently of the amplitudes and frequencies of the superimposed oscillations. The modulated blowing was a major factor in improving the performance of the airfoil at much lower energy inputs than was hitherto known. Optimum benefits in performance were obtained at reduced frequencies, based on the flap chord, of an order of unity. Significant increase in lift as well as cancellation of form drag were observed