Natural Laminar Flow Airfoil Research Articles

Robust design of natural laminar flow supercritical airfoil by multi-objective evolution method

A transonic, high Reynolds number natural laminar flow airfoil is designed and studied. The γ-θ transition model is combined with the shear stress transport (SST) k-w turbulence model to predict the transition region for a laminar-turbulent boundary layer. The non-uniform free-form deformation (NFFD) method based on the non-uniform rational B-spline (NURBS) basis function is introduced to the airfoil parameterization. The non-dominated sorting genetic algorithm-II (NSGA-II) is used as the search algorithm, and the surrogate model based on the Kriging models is introduced to improve the efficiency of the optimization system. The optimization system is set up based on the above technologies, and the robust design about the uncertainty of the Mach number is carried out for NASA0412 airfoil. The optimized airfoil is analyzed and compared with the original airfoil. The results show that natural laminar flow can be achieved on a supercritical airfoil to improve the aerodynamic characteristic of airfoils.

Pulsed Jets Laminar Separation Control Using Instability Exploitation

The physics of control by pulsed blowing on a NACA natural laminar flow airfoil is studied using hot-film anemometry. Measurements in the uncontrolled separated shear layer indicate that vortex shedding is taking place due to the Kelvin–Helmholtz-type inviscid instability. Steady and pulsed external acoustic excitation is used as well to decouple the frequency content of the perturbation from the vorticity introduced by the jet. Acoustic control introduces either the most unstable frequency or harmonics of carrier frequency in the most unstable range, which amplify exponentially in the separation region yielding a significant delay of the separation location to approximately 55% chord. Experimental data suggest that pulsed jets introduce higher-order harmonics of the low-frequency pulsing as well, amplifying the natural disturbances in the laminar separation. Phase-averaged wavelet analysis is used to study the control physics within a single pulsing period. It is shown that a jet-induced high-frequency content convects downstream of the jets at approximately the freestream velocity. A second packet of jet-induced frequency content is convected inside the boundary layer at a slower speed. As the second packet interacts with the laminar separation, natural vortex shedding is enhanced. The vortex shedding induces momentum near the wall and temporarily calms the separation. After the convected turbulent structures have passed, vortex shedding subsides, and the boundary layer briefly loses momentum near the wall until the next set of structures return.

Hybrid transition control approach for plasma actuators

This work reports on the development of a novel hybrid transition control method for single DBD plasma actuators. The experiments have been carried out on a natural laminar flow airfoil in a wind tunnel and combine two methods previously used for transition control purposes with DBD plasma actuators: boundary-layer stabilization by quasi-steady wall-parallel momentum addition, and active wave cancelation by linear superposition utilizing modulated momentum injection. For this purpose, the modulated body force is controlled using an improved extremum seeking controller based on an extended Kalman filter. Combining the two methods in a single actuator has advantages. Applied to 2-D Tollmien–Schlichting waves, the achievable transition delay in hybrid mode is significantly larger than the isolated effects, while the energy consumption remains almost unchanged compared to the case of continuous actuation. For a Reynolds number of $$Re=0.94 \cdot 10^6$$ , a transition delay of $${\Updelta}x/c=0.242$$ could be observed.

Active flow control of airfoil using mesh/meshless methods coupled to hierarchical genetic algorithms for drag reduction design

PurposeThe purpose of this paper is to investigate an active flow control technique called Shock Control Bump (SCB) for drag reduction using evolutionary algorithms.Design/methodology/approachA hierarchical genetic algorithm (HGA) consisting of multi‐fidelity models in three hierarchical topological layers is explored to speed up the design optimization process. The top layer consists of a single sub‐population operating on a precise model. On the middle layer, two sub‐populations operate on a model of intermediate accuracy. The bottom layer, consisting of four sub‐populations (two for each middle layer populations), operates on a coarse model. It is well‐known that genetic algorithms (GAs) are different from deterministic optimization tools in mimicking biological evolution based on Darwinian principle. In HGAs process, each population is handled by GA and the best genetic information obtained in the second or third layer migrates to the first or second layer for refinement.FindingsThe method was validated on a real life optimization problem consisting of two‐dimensional SCB design optimization installed on a natural laminar flow airfoil (RAE5243). Numerical results show that HGA is more efficient and achieves more drag reduction compared to a single population based GA.Originality/valueAlthough the idea of HGA approach is not new, the novelty of this paper is to combine it with mesh/meshless methods and multi‐fidelity flow analyzers. To take the full benefit of using hierarchical topology, the following conditions are implemented: the first layer uses a precise meshless Euler solver with fine cloud of points, the second layer uses a hybrid mesh/meshless Euler solver with intermediate mesh/clouds of points, the third layer uses a less fine mesh with Euler solver to explore efficiently the search space with large mutation span.

The Development of Very Light Jet with Unconventional Arrangement

In order to be economically viable and competitive, the current trends in designing very light jet aircraft have shown that it is essential to improve the aircraft performance and operational flexibility goal, nevertheless have an efficient cost. The application of unconventional configuration has attracted the designer to achieve that goal. This paper discusses the prospective design of unconventional arrangement which will be applied for very light jet aircraft. The existing of a very light jet configurations is reviewed. New concepts of unconventional configuration for this type of aircraft are discussed. The three-surface configuration is then proposed for the design project. The configuration offers stability and unobstructed cabin. With the appropriate design, the additional weight and interference drag due to the extra surface can be reduced. The new design of aircraft configuration and cabin are discussed. High Speed Natural Laminar Flow airfoil is applied to obtain High Lift/Drag Wing design. The weight and aircraft performances are then estimated. The predicted aircraft performance has satisfied the design requirements and objectives. The design process covered by this paper is only concentrate on initial design. The data from this paper can be continuing in future for the next step of design.

Drag minimization using active and passive flow control techniques

The objective of this paper is to appraise the practicability of weakening the shock wave and hereby reducing the wave drag in transonic flight regime using flow control devices such as two-dimensional contour bump, individual jet actuator, and also the hybrid control which includes both control devices together, and thereby to gain the desired improvements in aerodynamic performance of air-vehicle. To validate the numerical study, a natural laminar flow airfoil, Rae5243, is chosen and then comparisons with experimental data have been made before the optimization of flow control parameters. After validation study, an efficient gradient-based optimization technique is used to optimize 2D bump parameters including the length, the maximum height, the bump position via shock location, and the crest position via bump and also the jet actuation parameters such as mass flow coefficient, suction/blowing angle, actuation location over the upper surface of the airfoil. The process generally consists of using the simulation code to obtain a flow solution for given parameters and then search the optimum parameters to reduce the total drag of the airfoil via the optimizer. Most importantly, it is shown that, the optimization yields 3.94% decrease in the total drag and 5.03% increase in lift, varying the design parameters of active and passive control devices.

Design of the Grand Touring Sports Car Wing

This study evaluated the adaptation of natural laminar flow airfoils for Grand Touring (GT) sports car racing and the influence of wing geometry and flow control devices on rear-wing aerodynamics. The mean camber lines for the National Advisory Committee for Aeronautics (NACA) 651-412 and National Aeronautics and Space Administration (NASA) LS(1)-0413 airfoils were calculated. Numerical analysis was conducted using thin-airfoil theory and finite-wing theory. Airfoil variables included zero-lift angle of attack and centre-of-pressure location. Wing variables encompassed induced and effective angles of attack, lift and drag coefficients, and lift-to-drag ratio. Modelling consisted of variations in wing aspect ratio and the integration of end plates and a Gurney flap. A tapered rectangular planform is quasi-elliptical and attains near-unity Oswald efficiency. The NASA LS(1)-0413 airfoil is stall resistant and produces high downforce at the expense of extra drag because of factors related to camber, profile thickness, leading edge radius, and concave pressure recovery. The wing should be set at an incidence above that for best lift-to-drag ratio. The NACA 651-412 airfoil is aerodynamically more efficient but produces less downforce and may be used as a stabilizer. Augmented aspect ratio, end plates, and a Gurney flap enhance wing aerodynamics via flow control and modified downwash configuration. The analysis suggests that a tapered LS(1)-0413 wing of 5.56 aspect ratio fitted with end plates and a Gurney flap, set at high incidence, is an appealing single-element arrangement for applications in Grand Touring sports car engineering.

In-Flight Visualization of Supersonic Flow Transition Using Infrared Imaging

Infrared visualization was used to obtain information on the state of the boundary layer of a natural laminar flow airfoil in supersonic flight. In addition to the laminar/turbulent transition boundary, the infrared camera was able to detect shock waves and present a time-dependent view of the flow field. Thermal and flow mechanisms on the surface in flight were modeled numerically to aid in the design of the flight experiment and facilitate analysis of recorded infrared footage. A commercially available infrared camera was adapted for airborne use in this application. Readily available infrared technology has the capability to provide detailed visualization of various flow phenomena in subsonic to hypersonic flight regimes

Method for the Constrained Design of Natural Laminar Flow Airfoils

An automated iterative design method has been developed by which an airfoil with a substantial amount of natural laminar e ow can be designed while maintaining other aerodynamic and geometric constraints. Drag reductions have been realized using the design method over a range of Mach numbers, Reynolds numbers, and airfoil thicknesses. The key features of the method are the compressible linear stability analysis code used to calculate N-factors; the ability to calculate a target N-factor distribution that forces the e ow to undergo transition at the desired location; the target pressure/ N-factor relationship that is used to modify target pressures to produce the desired N-factor distribution; and its ability to design airfoils to meet lift, pitching moment, thickness, and leading-edge radius constraints while also being able to meet the natural laminar e ow constraint.

Appropriate Dynamic‐Stall Models for PerformancePredictions of VAWTs with NLF Blades

This paper illustrates the relative merits of using Natural Laminar Flow (NLF) airfoils in the design of Vertical Axis Wind Turbines (VAWT). This is achieved by the application of the double‐multiple‐streamtube model of Paraschivoiu to the performance predictions of VAWTs equipped with conventional and NLF blades. Furthermore, in order to clearly illustrate the potential benefit of reducing the drag, the individual contributions of lift and drag to power are presented. The dynamic‐stall phenomena are modelled using the method of Gormont as modified by several researchers. Among the various implementations of this dynamic‐stall model available in the literature, the most appropriate and general for NLF applications has been identified through detailed comparisons between predicted performances and experimental data. This selection process is presented in the paper. It has been demonstrated that the use ofNLF airfoils in VAWT applications can lead to significant improvements with respect to conventional design only in a very low wind speed range, the extent of which is negligible with respect to the VAWT operational wind speeds.

Design of a natural laminar flow airfoil for light aircraft

Design of a natural laminar flow airfoil for light aircraft

Design of a natural laminar flow airfoil for the light transport aircraft

As a substitute to the NASA GA(W)-2 airfoil, that is envisaged for a Light Transport Aircraft (LTA), a new airfoil NAL-MSNLF-136 is designed at NAL. It is shown according to model calculations that the thicker NAL airfoil shows better aerodynamic efficiency than the GA(W)-2 profile in the operatingC L range.

Surface wetting effects on a laminar flow airfoil in simulated heavyrain

Wind tunnel experiments have been conducted on a natural laminar flow airfoil in a simulated heavy rain of 440 mm/h at a Reynolds number of 310,000 to assess the effect of surface wettability on the performance degradation due to rain. A significant loss of performance was observed for each of the three surfaces tested with the nonwettable, waxed surface being the most degraded (-75% reduction in maximum L/D) and the incompletely wettable epoxy gel coat being the least (-45% reduction). Accompanying the L/D loss was an effective reduction in angle of attack of up to 2 deg resulting from a downward translation of the CL polar. In photographic observations, the runback water layer was found to bead on the wax surface and sheet on the wettable surfaces. The strong dependence on surface wettability of both the airfoil performance and the water behavior indicates that the degradation due to heavy rain is primarily a result of the roughening of the airfoil surface by the runback water layer. The observed performance loss could only be partially emulated by causing premature transition from a laminar to a turbulent boundary layer. Nomenclature CL =lift coefficient, based on chord CD =drag coefficient, based on chord D = drop or bead diameter h = height of water layer L/D = lift-to-drag ratio U = flow velocity We = Weber number OL = angle of attack 0 = contact angle p = air density a = surface tension