Showing papers on "Airfoil published in 2016"

Performance and Energy Expenditure of Coflow Jet Airfoil with Variation of Mach Number

Abstract: This paper conducts a numerical and experimental investigation of a coflow jet airfoil to quantify lift enhancement, drag reduction, and energy expenditure at a Mach number range from 0.03 to 0.4. The jet momentum coefficient is held constant at 0.08, and the angle of attack varies from 0 to 30 deg. The two-dimensional flow is simulated using a Reynolds–averaged Navier–Stokes solver with a fifth-order-weighted essentially non-oscillatory scheme for the inviscid flux and a fourth-order central differencing for the viscous terms. Turbulence is simulated with the one equation Spalart–Allmaras model. The predicted coflow jet pumping power has an excellent agreement with the experiment. At a constant Mach number, the power coefficient is decreased when the angle of attack is increased from 0 to 15 deg. When the Mach number is increased from 0.03 to 0.3, the suction effect behind the airfoil leading edge is further augmented due to the compressibility effect. This results in an increased maximum lift coefficien...

Transition Flight Modeling of a Fixed-Wing VTOL UAV

Abstract: This paper describes a complete six-degree-of-freedom nonlinear mathematical model of a tilt rotor unmanned aerial vehicle (UAV). The model is specifically tailored for the design of a hover to forward flight and forward flight to hover transition control system. In that respect, the model includes the aerodynamic effect of propeller-induced airstream which is a function of cruise speed, tilt angle and angle of attack. The cross-section area and output velocity of the propeller-induced airstream are calculated with momentum theory. The projected area on the UAV body that is affected by the propeller-induced airstream is specified and 2D aerodynamic analyses are performed for the airfoil profile of this region. Lookup-tables are generated and implemented in the nonlinear mathematical model. In addition, aerodynamic coefficients of the airframe are calculated by using CFD method and these data are embedded into the nonlinear model as a lookup-table form. In the transition flight regime, both aerodynamic and thrust forces act on the UAV body and the superimposed dynamics become very complex. Hence, it is important to define a method for hover-to-cruise and cruise-to-hover transitions. To this end, both transition scenarios are designed and a state-schedule is developed for flight velocity, angle of attack, and thrust levels of each of the thrust-propellers. This transition state schedule is used as a feedforward state for the flight control system. We present the simulation results of the transition control system and show the successful transition of TURAC in experiment.

Investigation of the Unsteady Flow and Noise Generation in a Slat Cove

Abstract: This study presents hybrid Reynolds-averaged Navier–Stokes/large-eddy simulations of the unsteady flow and noise-generation phenomena in the slat cove of a high-lift wing profile. These computations are part of a joint numerical/experimental aeroacoustics collaborative program dedicated to slat-flow analysis. A dedicated two-element wing profile (slat plus main body) has been designed to isolate slat noise from other possible sources (e.g., the flap), while minimizing mean flow deflection effects, to improve the fidelity of open-jet wind-tunnel measurements. The design of this two-element airfoil has been performed numerically, using an optimization process based on steady Reynolds-averaged Navier–Stokes calculations. This airfoil has been investigated experimentally at the Ecole Centrale de Lyon open jet facility. Unsteady zonal hybrid Reynolds-averaged Navier–Stokes/large-eddy simulations have been performed to provide a comprehensive description of the unsteady flow inside the slat cove, focusing on th...

Flow topology and acoustic emissions of trailing edge serrations at incidence

Abstract: The flow past a NACA 0018 airfoil with sawtooth trailing edge serrations has been investigated using stereoscopic particle image velocimetry (PIV). The serration flap angle and airfoil incidence are varied in order to study the effect of secondary flow establishing between the suction and pressure sides of the serrations. The flow topology around the serrations is inferred from the analysis of time-averaged streamlines close to the airfoil surface and from the wall-normal flow velocity in between serrations. Additional PIV measurements with a plane in cross-flow highlight the formation of streamwise vortex pairs. The flow behavior is further characterized in terms of its turbulence statistics. Noise emissions are measured with an acoustic phased array in combination with beamforming. The serrations are found to be effective in reducing noise, and their application is studied for different degrees of airfoil incidence and serration flap angle.

Coherent Structures in the Transition Process of a Laminar Separation Bubble

Abstract: Coherent structures formed within the laminar separation bubble on the suction side of a NACA 0018 airfoil at a chord Reynolds number of 100,000 and an angle of attack of 5 deg are investigated experimentally using a combination of surface pressure measurements; time-resolved flow visualization; and time-resolved planar two-component particle image velocimetry. The results show that strongly periodic shear-layer vortices form in the separation bubble due to the amplification of disturbances in the fore portion of the bubble. These structures feature strong spanwise coherence at rollup; however, they deform rapidly upstream of the mean reattachment location. Spanwise undulations in the vortex filaments develop in a nonperiodic fashion, with the spanwise wavelength shown to be approximately two times the streamwise spacing of the shed structures. It is demonstrated that these spanwise deformations lead to regions of local vortex breakup, which expand rapidly as the vortices approach the mean reattachment po...

Vane assembly for a gas turbine engine

Abstract: A vane assembly (10) for a gas turbine engine is disclosed herein. The vane assembly includes an inner platform, an outer platform, and a ceramic-containing airfoil (16) that extends from the inner platform to the outer platform. The ceramic-containing airfoil is manufactured to have radially discontinuous ribs (25) spaced radially apart from one another between the inner platform and the outer platform.

Boundary layer characterization and acoustic measurements of flow-aligned trailing edge serrations

Abstract: Trailing edge serrations designed to reduce airfoil self-noise are retrofitted on a NACA 0018 airfoil. An investigation of the boundary layer flow statistical properties is performed using time-resolved stereoscopic PIV. Three streamwise locations over the edge of the serrations are compared. An analysis of the results indicates that, while there is no upstream effect, the flow experiences significant changes as it convects over the serrations and toward its edges. Among the most important, a reduced shear stress and modifications of the turbulence spectra suggest beneficial changes in the unsteady surface pressure that would result in a reduction of trailing edge noise. Microphone array measurements are additionally performed to confirm that noise reduction is indeed observed by the application of the chosen serration design over the unmodified airfoil.

Aerodynamic and aeroacoustic performance of airfoils with morphing structures

Abstract: Aerodynamic and aeroacoustic performance of airfoils fitted with morphing trailing edges are investigated using a coupled structure/fluid/noise model. The control of the flow over the surface of an airfoil using shape optimization techniques can significantly improve the load distribution along the chord and span lengths whilst minimising noise generation. In this study, a NACA 63-418 airfoil is fitted with a morphing flap and various morphing profiles are considered with two features that distinguish them from conventional flaps: they are conformal and do not rely on conventional internal mechanisms. A novel design of a morphing flap using a zero Poisson’s ratio honeycomb core with tailored bending stiffness is developed and investigated using the finite element model. While tailoring the bending stiffness along the chord of the flap yields large flap deflections, it also enables profile tailoring of the deformed structure which is shown to significantly affect airfoil noise generation. The aeroacoustic behaviour of the airfoil is studied using a semi-empirical airfoil noise prediction model. Results show that the morphing flap can effectively reduce the airfoil trailing edge noise over a wide range of flow speeds and angles of attack. It is also shown that appropriate morphing profile tailoring improves the effect of morphing trailing edge on the aerodynamic and aeroacoustic performance of the airfoil.

Aerodynamic shape optimization and analysis of small wind turbine blades employing the Viterna approach for post-stall region

Abstract: This paper aims to optimize the distribution of chord and twist angle of small wind turbine blade in order to maximize its Annual Energy Production (AEP). A horizontal-axis wind turbine (HAWT) blade is optimized using a calculation code based on the Blade Element Momentum (BEM) theory. A difficult task in the implementation of the BEM theory is the correct representation of the lift and drag coefficients at post-stall regime. In this research, the method based on the Viterna equations was used for extrapolating airfoil data into the post-stall regime and the results were compared with various mathematical models. Results showed the high capability of this method to predict the performance of wind turbines. Evaluation of the efficiency of wind turbine blade designed with the proposed model shows that the optimum design parameters gave rise to an increase of 8.51% in the AEP rate as compared with the corresponding manufactured operating parameters.

Design optimization of the aerodynamic passive flow control on NACA 4415 airfoil using vortex generators

Abstract: The present paper provides an experimental optimization of a NACA 4415 airfoil equipped with vortex generators (VGs) to control its flow separation. To build this optimal configuration an experimental parametric study was conducted on five geometrical parameters: thickness and height of vortex generators, position, orientation angle with respect to the mean flow direction, spacing in the spanwise direction. Moreover, a new configuration that includes micro generators behind the conventional ones was also investigated as a potentially interesting solution. For all these cases wind tunnel tests were performed and compared for different angles of attack and various Reynolds numbers up to 2 10 5 . These experiments enabled us to highlight the main trends to get an optimal design, for which quantitative improvement can be achieved by passive means in terms of aerodynamic performances on NACA4415 airfoil. The results reveal that triangular shape vortex generators are best suited to control boundary layer separation. An optimum angle of VGs is obtained for 12°with a 3 mm distance between vortex generators located at 50% of the chord. It was found that micro vortex generators are very effective in controlling the flow with less parasite drag. The maximum lift coefficient for an airfoil with coupled vortex generators increases by 21% and a flow separation is delayed by 17°. However, this very good performance is counterbalanced by the appearance of parasitic drag. Indeed, it creates a counter-rotating array of vortices with the second raw of micro-vortex generators that reinforce the vortexes strength without any increase in device height.

Acoustic Characterization and Prediction of Representative, Small-Scale Rotary-Wing Unmanned Aircraft System Components

Abstract: In this study, hover performance and acoustic measurements are taken on two different isolated rotors representative of small-scale rotary-wing unmanned aircraft systems (UAS) for a range of rotation rates Each rotor system consists of two fixed-pitch blades powered by a brushless motor For nearly the same thrust condition, significant differences in overall sound pressure level (OASPL), up to 8 dB, and directivity were observed between the two rotor systems Differences are shown to be in part attributed to different rotor tip speeds, along with increased broadband and motor noise levels In addition to acoustic measurements, aeroacoustic predictions were implemented in order to better understand the noise content of the rotor systems Numerical aerodynamic predictions were computed using the unsteady Reynoldsaveraged Navier Stokes code OVERFLOW2 on one of the isolated rotors, while analytical predictions were computed using the Propeller Analysis System of the Aircraft NOise Prediction Program (ANOPP-PAS) on the two rotor configurations Preliminary semi-empirical frequency domain broadband noise predictions were also carried out based on airfoil self-noise theory in a rotational reference frame The prediction techniques further supported trends identified in the experimental data analysis The brushless motors were observed to be important noise contributors and warrant further investigation It is believed that UAS acoustic prediction capabilities must consider both rotor and motor components as part of a combined noise-generating system

Transonic airfoil performance enhancement using co-flow jet active flow control

Abstract: This paper performs a numerical proof of concept study to enhance transonic supercritical airfoil cruise performance using Co-Flow Jet(CFJ) active flow control technique. The Reynolds averaged Navier-Stokes(RANS) equations with one-equation Spalart-Allmaras turbulence model is used. A 5th order weighted essentially non-oscillatory(WENO) scheme with a low diffusion Riemann solver is utilized to evaluate the inviscid fluxes. A 4th order central differencing scheme matching the stencil width of the WENO scheme is employed for the viscous terms. Numerical trade studies are carried out to investigate the CFJ geometric effects on the performance enhancement. This research discovers that CFJ can significantly enhance the aerodynamic performance of RAE2822 transonic supercritical airfoil for both lift coefficient CL and aerodynamic efficiency ( L D )c that includes the CFJ pumping power. For the free-stream condition of M∞=0.729, Re∞=6.5× 10 , and AoA from 0 to 5.5, the CFJ RAE2822 airfoil is able to achieve a performance enhancement with both CL and ( L D )c increased simultaneously by 18.7% and 14.5%, respectively at the peak aerodynamic efficiency point. At the maximum lift coefficient point, the CFJ airfoil is able to increase the CL from 0.93 to 1.16 by 25.6% while slight decreasing the ( L D )c from 21.3 to 19.6. Rigorous mesh refinement study is conducted to ensure solution convergence of the numerical results. Since the baseline airfoil drag is over-predicted by more than 30% due to the inadequacy of the RANS model, the predicted improvement of the CFJ airfoil tends to be on the conservative side. The unique feature of CFJ airfoil to augment lift and reduce drag at low energy expenditure is shown to be able to drastically improve the transonic airfoil cruise performance when the flow is benign at low AoA. The performance enhancement of CFJ transonic airfoil needs to be further proved by wind tunnel experiment as the next step. It is hoped that this research will open a door to significantly enhance transonic airfoil performance since the supercritical airfoil was invented in 1960’s.

Aerodynamic Shape Optimization for Natural Laminar Flow Using a Discrete-Adjoint Approach

Abstract: A framework for the design of natural-laminar-flow airfoils is developed based on multipoint aerodynamic shape optimization capable of efficiently incorporating and exploiting laminar–turbulent transition. A two-dimensional Reynolds–averaged Navier–Stokes flow solver making use of the Spalart–Allmaras turbulence model is extended to incorporate an iterative laminar–turbulent transition prediction methodology. The natural transition locations due to Tollmien–Schlichting instabilities are predicted using a simplified eN method or the compressible form of the Arnal–Habiballah–Delcourt criterion. The Reynolds–averaged Navier–Stokes solver is subsequently used in a gradient-based sequential quadratic programming shape optimization framework. The transition criteria are tightly coupled into the objective and gradient evaluations. The gradients are obtained using an augmented discrete-adjoint formulation for nonlocal transition criteria. Robust design over a range of cruise flight conditions is demonstrated thro...

Woven type smart soft composite for soft morphing car spoiler

Abstract: Morphing structures making use of smart materials are considered to be a promising technology for the amelioration of the aerodynamic performance of land and air vehicles. In particular, soft morphing structures are capable of continuous curvilinear structural deformation upon actuation without discrete sections that generate aerodynamic losses. In this paper, a woven type smart soft composite consisting of shape memory alloy wires and glass fiber-reinforced composite was fabricated and applied to the rear spoiler of a ⅛-scaled radio-controlled car which is capable of actuating either symmetrically or asymmetrically. To verify its aerodynamic performance, wind tunnel experiments were carried out using a stand-alone spoiler under various wind speeds, angles of attack, and actuation modes. First, the results of the symmetric mode of actuation intended for braking conditions are presented. Second, to generate a yawing moment to assist the vehicle in cornering, the asymmetric mode of actuation was tested in an open-circuit blowing-type wind tunnel. Results of the symmetric and asymmetric modes of actuation were then compared with a symmetric airfoil (NACA 0010) with a flap tested under the same conditions. Lastly, the spoiler was mounted on the small-scale car and wind tunnel tests were conducted to determine the potential of augmentation on aerodynamic performance by implementing the soft morphing spoiler.