Clark-Y Airfoil Research Articles

The effect of vortex generators having Clark-Y airfoil on tapered swept-back wing

In the experimental study, the effects of vortex generators (VGs) having Clark-Y airfoil and triangular VGs are investigated. The tests were carried out on a tapered swept-back wing at Re = 6.0×104 using counter-rotating vortex generators having Clark-Y airfoil at five different locations that are x/c= 0.1, 0.2, 0.3, 0.4, and 0.5 and triangular VGs at x/c=0.1 location. A load cell is used to measure forces at angles of attack (AoA) ranging from 0° to 30°. It is observed that the maximum lift coefficient (CLmax) and aerodynamic performance of VGs having Clark-Y airfoil decrease when the position of the vortex generators changes from 0.1 to 0.5. The optimal results obtained from the study show that the tapered swept-back wing with the VGs having Clark-Y airfoil exhibits a significant increase of 37.5% in the CLmax and approximately 55% in the lift to drag ratio (L/D) at x/c=0.1 compared to the baseline. At low AoA, the VGs having Clark-Y airfoil provided better lift, whereas at high AoA, the triangular VGs provided better lift.

Investigation of aerodynamic performance of Clark-Y airfoil with more realistic tubercle model and internal slots

An experimental study is conducted to research the combined effect of leading-edge (LE) tubercles and internal slots on the Clark-Y airfoil at Reynolds numbers (Re) of 5.0×104, 7.5×104, and 1.0×105 for angles of attack ranging from 0° to 30°. The Clark-Y is a cambered airfoil that performs well at low and medium Reynolds numbers, having a maximum thickness of 11.7% at 28% of the chord. Five different test models are the subjects of experiments, one of which is the baseline. The other test models are the Wavy model, which has LE tubercles, and the Wavy with three different slot positions: the Wavy-LES (leading-edge slot), the Wavy-MS (middle slot), and the Wavy-TES (trailing-edge slot). The LE tubercle geometry is formed by the sum of two sinusoidal wave functions with a realistic approach. In the present work, experimental studies are performed through force measurements, and detailed information on a 3-dimensional flow field is obtained by a surface-oil flow visualization technique. Force measurements indicate that the Wavy model delays stall and exhibits smoother stall behavior compared to the baseline. Moreover, the findings show that the lift coefficient (CL) of the Wavy model deteriorates in the pre-stall region with the inclusion of the internal slots but improves significantly in the post-stall region. Maximum improvement in CL in the post-stall region was achieved by 60% in Wavy-LES at Re of 5.0×104 as compared to the baseline. At Re of 5.0×104, Wavy and Wavy-MS present a better lift-to-drag ratio (CL/CD) than the other models in the pre-stall region, whereas the baseline is the best at Re of 1.0×105. The best CL/CD is achieved by Wavy-LES in the post-stall region, regardless of the Reynolds numbers. The variation of flow characteristics relevant to aerodynamic performance is revealed by surface oil flow visualization for all tested models.

Experimental flow control investigation over suction surface of turbine blade with local surface passive oscillation

Impact of the local flexible membrane (LFM) on aerodynamic phenomena including the formation of a laminar separation bubble (LSB) and transition to turbulence was experimentally investigated over the suction surface of a Clark-Y airfoil first time in literature. The experiments such as aerodynamic force measurement, smoke-wire flow visualization and hot-film tests were carried out at the free-stream velocity of U∞ = 3.2 m/s, U∞ = 6.4 m/s, U∞ = 9.6 m/s, U∞ = 12.8 m/s, and Reynolds number based upon on the chord length was Rec = 3.5 × 104, Rec = 7.0 × 104, Rec = 1.05 × 105 and Rec = 1.4 × 105, respectively. The experimental angle of attack was set at 0° = α ≤ 20°. In detailed intermittency analysis by the hot-film sensor over the uncontrolled airfoil, it was seen that the LSB and transition to turbulence formed close to the trailing edge at a lower angle of attack, and it moved towards the leading edge when increasing the angle of attack simultaneously. Employing LFM on the suction surface obviously affected the progress of these flow phenomena. In the results of smoke-wire flow visualization, either the size of the laminar separation bubble (LSB) was reduced or its presence was suppressed at lower incidences. The aerodynamic force measurement results also supported those behaviors. In particular, at lower incidences, the negative effects of LSB were mitigated, resulting in the presence of a more stable lift curve. Additionally, it was clearly observed that utilizing LFM ensured positive effects, especially at the pre- and the post-stall regions in terms of fewer fluctuations at the CL curve, meaning that less aerodynamic vibration and noise on wind/hydro turbine could be obtained.

Drag Reduction by Uniform Blowing on the Pressure Surface of an Airfoil

Drag reduction effect by uniform blowing (UB) on the pressure surface of an airfoil is investigated through wind-tunnel experiments. The experiments are conducted using a Clark-Y airfoil model. The UB is realized by supplying air from an external compressor to a chamber, covered with a porous surface, installed near the leading edge of the pressure surface of the airfoil model. To investigate the effect of UB on friction drag, velocity profiles in the boundary layer on the pressure surface are measured using a hot-wire anemometer, and it is confirmed that the velocity profiles shift away from the airfoil surface by UB. The local friction drag reduction rate is quantitatively evaluated by using the law of the wall, and about 50% local friction drag reduction is confirmed by UB at 0.33% of the freestream velocity at the chord Reynolds number . Besides, the pressure distribution in the wake is measured with a pitot tube to investigate the effect of UB on the total drag. The measurement result indicates that the total drag is reduced by UB about 5%, although the measurement uncertainty is estimated to be on the same order.

Adjoint-Based Sensitivity Analysis for Airfoil Flow Control Aiming at Lift-to-Drag Ratio Improvement

Sensitivities of drag and lift to body force and blowing/suction are investigated based on a continuous adjoint method through Reynolds-averaged Navier–Stokes simulation (RANS). For a Clark-Y airfoil, changes in the drag, the lift, and the lift-to-drag ratio are found to be caused by different mechanisms depending on the type and locations of control input. Improvement in the lift-to-drag ratio by body forces is achieved by both pressure drag reduction and pressure lift enhancement. The effective angle for blowing/suction is nearly normal to the surface, and blowing around the leading edge and blowing/suction on the lower/upper surface near the trailing edge improve the lift-to-drag ratio effectively. Investigation on the control amplitude reveals that the present sensitivity analysis is valid when the blowing/suction velocity is less than 1% of the freestream velocity. The sensitivities are observed to be slightly weakened by decreasing the Reynolds number due to the difference in the baseline drag and lift coefficients, whereas the higher angle of attack is found to raise the sensitivities. Finally, the similar sensitivity analysis is performed also for NACA4412 and NACA0012, and it is found that slight differences in the shape result in substantial differences in the sensitivities.

Pressure-based lift estimation and its application to feedforward load control employing trailing-edge flaps

Abstract. This experimental load control study presents results of an active trailing-edge flap feedforward controller for wind turbine applications. The controller input is derived from pressure-based lift estimation methods that rely either on a quasi-steady method, based on a three-hole probe, or on an unsteady method that is based on three selected surface pressure ports. Furthermore, a standard feedback controller, based on force balance measurements, is compared to the feedforward control. A Clark-Y airfoil is employed for the wing that is equipped with a trailing-edge flap of x/c=30% chordwise extension. Inflow disturbances are created by a two-dimensional active grid. The Reynolds number is Re=290 000, and reduced frequencies of k=0.07 up to k=0.32 are analyzed. Within the first part of the paper, the lift estimation methods are compared. The surface-pressure-based method shows generally more accurate results, whereas the three-hole probe estimate overpredicts the lift amplitudes with increasing frequencies. Nonetheless, employing the latter as input to the feedforward controller is more promising as a beneficial phase lead is introduced by this method. A successful load alleviation was achieved up to reduced frequencies of k=0.192.

Analysis of the effect of freestream turbulence on dynamic stall of wind turbine blades

The aerodynamics of a wind turbine blade at various fixed and dynamically changing angles of attack for laminar and turbulent freestream is investigated by large-eddy simulations. The effects of freestream turbulence on the aerodynamic coefficients are analyzed for dynamic stall conditions being generated by prescribing gusts, i.e., periodically changing incoming velocity fields, onto a ClarkY airfoil at a chord based Reynolds number of Re=150,000. A synthetic turbulence generation (STG) method is extended and applied to produce the turbulent gusts in a time varying mean flow with predefined turbulence statistics, such as mean velocity, Reynolds stress tensor components, and velocity spectra. The length scales in the turbulent freestream are smaller than the blade chord length. The reduced frequency of the incoming laminar and turbulent gusts is kred=0.2 based on the freestream velocity, chord length, and gust frequency. Dynamic stall is analyzed for an angle of attack ranging from 10° to 25°. It is shown how much the freestream turbulence level delays stall and increases lift at high angle of attack. The effect of the turbulence is most evident on the aerodynamic forces during the phase of decreasing angle of attack of the dynamic stall process, in which the reattachment of the boundary layer is enhanced by the freestream turbulence. The negative damping from the moment coefficient is also significantly reduced due to the incoming turbulence. The results show that the freestream turbulence in a turbulent flow at a turbulence level of 5% improves the aerodynamic performance of the wind turbine blade.

Aero-Driven Bleed-Air Applied to Roll Control

Aero-driven bleed-air (ADB) is a flow control technology that offers a unique alternative to novel aircraft concepts that are not conducive to traditional flapped control surfaces. The primary source of mechanical energy for ADB control is derived from the motion of the vehicle. Inherent pressure differences across aerodynamic surfaces are communicated by means of internal channels, with the intent of affecting the local crossflow. Effected across a large area, ADB can significantly alter the global aerodynamic forces and moments. This investigation explores the performance of large-area-distributed ADB as a roll control mechanism on a low-speed, fixed-wing air vehicle. A series of wind tunnel experiments is presented, aimed at characterizing the effects that various porosity configurations have on the lift and drag of a Clark-Y airfoil section. ADB was found to be capable of reducing the sectional lift coefficient across a broad domain of angles of attack () by as much as relative to the baseline airfoil. A mathematical model for estimating the steady-state roll rate of a wing with ADB is developed. Several pore opening schedules are considered, with an emphasis on finding a nearly linear relationship between bleed level and steady-state roll rate. The selected schedule is implemented on a flight test vehicle equipped with ADB roll control effectors. Roll rates of up to were achieved in flight, and flight test data were found to validate the steady-state roll rate model. The aircraft was piloted from takeoff through landing using ADB for roll control.

Parametric study toward optimization of blowing and suction locations for improving lift-to-drag ratio on a Clark-Y airfoil

Reynolds-averaged Navier–Stokes simulations (RANS) of flows around a Clark-Y airfoil with uniform blowing (UB) and uniform suction (US) are performed aiming at improvement of the airfoil performance. First, the control effect in the case with single UB or US applied on the airfoil surface is investigated at the various control locations. The magnitude of UB/US is 0.14% of the free-stream velocity, and the control region is set at four different locations on the upper and lower surfaces. The Reynolds number based on the chord length and the angle of attack are 1.5 × 106 and 0°, respectively. It is found that the friction drag is decreased/increased by single UB/US control. It is also found that UB on the lower surface or US on the upper surface improves the lift-to-drag ratio, while UB on the upper surface or US on the lower surface worsens it. In the combined control of UB and US having the equal flow rate, the magnitude of blowing and suction is set at 0.14% or 0.26% of the free-stream velocity. The locations of blowing/suction and flow conditions are the same as those in the cases with either UB or US only. The simulation result suggests that the lift-to-drag ratio is improved by the combined control of UB on the lower surface and US on the upper surface. In particular, the lift-to-drag ratio is most improved by a combination of UB on the lower rear surface and US on the upper rear surface. In contrast, a combined control of UB on the upper front surface and US on the lower rear surface is identified as the most effective case for the friction drag reduction only.

Assessment of Friction Drag Reduction on a Clark-Y Airfoil by Uniform Blowing

Effects of uniform blowing on a Clark-Y airfoil are investigated experimentally aiming at turbulent friction drag reduction. The uniform blowing is applied on the rear part of the upper surface. The experiment is carried out at the free-stream velocity of , and the Reynolds number based on the chord length is . The angle of attack is set to and 6°. In the velocity measurement by a hot-wire anemometry, the velocity profile in the blowing region is found to shift away from the wall. This behavior is consistent with that observed in the previous studies on a flat plate, and it qualitatively suggests that the local friction drag is reduced by uniform blowing. Subsequently, this study attempts a quantitative assessment of the local friction drag reduction rates by fitting the mean velocity profile to the log-law taking into account the pressure gradient and the blowing effect. From this, this study has confirmed about 20–40% local friction drag reduction due to blowing. Unfortunately, however, the total drag estimated from the wake pressure profile is found to increase slightly by blowing.

Numerical Investigation of Local Flexible Membranes Effects on Separated Laminar and Transient Flows

Objectives: The purpose of this study is a numerically investigation of aerodynamic characteristics of NACA0012 and Clark-Y airfoils with Local Flexible Membrane (LFM) in laminar and transient flows respectively. Novelty: A pressure based algorithm using a finite volume element method has been used to solve Navier-Stokes equations and the unique feature of the present method is the physical scheme influencing the convection fluxes at cell surfaces. Method: We have focused on the effects of deformation of the membrane on aerodynamic characteristics. First, we have solved the flow on NACA0012 airfoil in Reynolds number of 5000 and investigated the effects of LFM on aerodynamic coefficients in laminar flow. Then, we have solved the flow over Clark-Y airfoil in Reynolds number of 300000 and studied the effects of LFM in transient flow. To calculate the Reynolds stresses, transient γ - Reθ model has been used. Finding: According to the results, in laminar flow, the LFM prevents flow separation. In transient flow, the membrane by oscillation prevents flow separation, reduces drag coefficients, increases lift coefficients and delays the stall angle.

Flexible Rod Design for Educational Wind Balance

This article provides a technical description of a flexible hinge for wind tunnel rigs. For academic purposes, the device was integrated into several rod flexures to build a home-made external wind balance system. The cylindrical elastic element incorporates several notches, and the flexure linkage is able to transmit force in the main axial direction without hindering perpendicular movement. The flexural element described here is simple and easily manufactured, and can also be used with other types of wind balance. The flexure described in this article has similar functionality to those mentioned in the reference section, but has a more compact element. The project’s effectiveness was demonstrated in a series of experimental comparisons of forces and moments measured on a wing using the N.A.C.A. Clark-Y airfoil profile.

Винтокольцевой движитель для беспилотного летательного аппарата

Small and medium Unmanned Aerial Vehicles use piston engines with different kind of propulsion systems, that incorporate propeller concept. Existed design and optimization methods give possibility to find optimal solution for certain application. Usage appropriately shaped circular housing or duct around propeller in some case sufficiently increase performance, compared to typical propeller. This study aimed made design of ducted fan propulsion system by complex design methods with thrust about 300 kg. Complex method described here incorporate panel-vortex method as design tools, and finite volume analysis for performance calculation.General parameters and geometry of propulsor was determined at first stage. Assumed that propulsor should generate 300 kg of thrust with 136 hp engine power. Input data for propeller design was circular housing geometry. Clark-Y airfoil data used for geometry of circular housing around propeller. After parameters calculation complete propulsor geometry was generated.Propeller have four blades, after propeller installed static contra-propeller for recovering wake energy with five blades. Blade shape specified by planform and four control section with appropriate airfoil and twist. With this geometry data perfomance calculation was made at second stage.Second stage calculations are carried out in CFD codes, which implements finite-volume analysis. Results are thrust and speed/pressure spatial distribution at two differ flight condition – zero speed at ground and 50 m/s at sea level.Concluded that circular housing add 15…20% extra thrust with same power of engine. Rotation speed should not increase for propeller with 1.5 m diameter, because blade tip have supersonic speed, drag dramatically increased, vibration occurs, as result a significant loss of thrust.Obtained speed and pressure spatial distribution around propulsor given information about stall region, and help with further improvement of propulsor.

Effect of Different Airfoils on Performance of Axial Fan

Airfoil has great influence on the performance of axial fan. In order to study performance of axial fan. Four kinds of airfoils have been applied to optimize the impeller of axial fan. The 3D internal flows of the axial fan under different operating conditions were simulated based on a steady numerical method in ANSYS CFX 14.5. The results show that the curve of total pressure of the fan with LS airfoil blades is slightly steeper, and that of the fan with CLARK-Y(C=11.7%) (C is the blade thickness ratio) airfoil blades is relatively flat. The total pressure of the axial fan with CLARK-Y(C=11.7%) blades is highest among others. While achieving the highest efficiency in all the operating conditions except the lowest flow rate. Moreover, the blades loading of the CLARK-Y(C=11.7%) airfoil blades fan is entirely more uniform than that in others. The turbulent kinetic energy distribution on the leading edge of blades shows that the axial fan with CLARK-Y(C=11.7%) airfoil blades fan can improve the turbulent kinetic energy effectively.

Experimental Evaluation of an Internally Passively Pressurized Circulation Control Propeller

The purpose of circulation control for fixed wing aircrafts is to increase the lifting force when large lifting forces and/or slow speeds are required, such as at takeoff and landing. Wing flaps and slats are used on almost all fixed-wing aircraft. While effective in increasing lift, they do so with penalty of increasing drag, weight, and control complexity. The goal of this research was to find an alternative way of pumping pressurized air to the trailing edge slot on a UAV propeller. This design called for rerouting stagnation pressure from the frontal propeller area through the inside of the propeller blades to ejection slots on the trailing edge. This allows for the forward velocity of the aircraft to drive the pressurization of the circulation control plenum passively, without additional hardware. For this study, a Clark-Y airfoil section propeller with an overall diameter of 0.609 meters was designed and tested. The comparison of the augmented to unaugmented propeller showed a 5.12 percent increase in efficiency, which is shown to act over the entire range of flight envelopes of the aircraft and is shown to be particularly beneficial at advance ratios above 0.30, normal operating conditions of propeller-driven UAVs.

익형 동체의 하강기류(Down-wash)가 공기역학적 특성에 미치는 영향에 관한 수치해석연구

Drag reduction of a running vehicle is very important issue for the energy savings and emission reduction of its power train. Especially for a solar powered electric vehicle, the drag reduction and weight lightening are two serious problems to be solved to extend its driving distance under the given energy condition. In this study, the ground effect of an airfoil shaped road vehicle was studied for an optimum body design of an ultra-light solar powered electric vehicle. Clark-Y airfoil type was adopted to the body shape of the model vehicle to reduce aerodynamic drag. From the study, it was found that the drag of the model vehicle was reduced as the height(h) between ground and the lower surface of the model vehicle was decreased. It is due to the reduction of the down-wash decreasing the induced drag of the vehicle. The lift was also decreased as the height decreased. It is due to the turbulent boundary layer developed beneath the vehicle body. The drag is classified into two types; the form and friction drag. The fraction of form drag to friction one is 76 to 24 on the model vehicle. As the height(h) of the model vehicle from the ground surface increases the form drag also increases but the friction drag is in reverse.

모핑 에어포일 형상의 공력특성 실험연구

The present paper is the preliminary study of the development of a morphing aircraft wing and investigates experimently the aerodynamic characteristics of a base airfoil and a morphing airfoil. The wind tunnel tests are conducted for a base Clark-Y airfoil, an airfoil with a mechanical flap, and a morphing airfoil. Lifts, drags, and pitching moments are measured by using a three-axis load cell and they are calibrated by considering solid blockage and wake blockage. The wind tunnel tests are conducted for various air speeds, Reynolds’ numbers, and angles of attack. The experimental results show that the aerodynamic characteristics of the morphing airfoil in lift-drag and lift-pitching moment are better than those of the airfoil with a mechanical flap.

1600kW급 프로펠러 블레이드 공력설계 및 해석

Propeller shall have high efficiency and improved aerodynamic characteristics to get the thrust to fly at high speed for the turboprop aircraft. That is way Clark-Y airfoil which is used to conventional 1600kW class aircraft propeller is selected as a blade airfoil. Adkins method is used for aerodynamic design and performance analysis with respect to the propeller design point. Adkins method is based on the vortex-blade element theory which design the propeller to satisfy the condition for minimum energy loss. propeller geometry is generated by varying chord length and pitch angle at design point of turboprop aircraft. The propeller design results indicate that is evaluated to be properly constructed, through analysis of propeller aerodynamic characteristics using the Meshless method and MRF, SM method.

A111 プロトタイプMg合金製小型垂直軸風車の設計および性能評価(OS2 再生可能エネルギー)

In this paper, further evaluations of performances of prototype Mg-alloy micro vertical axis wind turbine were conducted. In addition, a comparative study of airfoils for vertical wind turbine was conducted; they are a prototyped airfoil based on the Clark-Y airfoil, a numerically optimized airfoil; NUT airfoil, and NACA0018 airfoil. At first, aerodynamics coefficients of lift, drag and momentum centered at the quarter of chord length at various angles of attack were clarified for those airfoils by 2-D steady CFD analysis. Typical Reynolds number were set around 3.3×10^4 for a portable-type micro VAWT system. We also examined a torque variation generated from wings with these airfoils using 3-D unsteady CFD analysis. The optimized airfoil; NUT airfoil has higher torque than NACA0018 airfoil, thus it will bring a promising improvement of power of micro VAWT.

Effects of Surface Flats on the Performance of a Remotely Piloted Aircraft

T HE characterization of the aerodynamic performance of airfoils has been the subject of focused study since the 1910s. An implicitly assumed requirement is that the model fidelity (experimental or computational) is such that it is an exact rendering of the proposed full-scale flight article. In many instances, however, the actual wing profile may not be representative of its design. Generally, this becomes a greater issue as the size and dimensions of the vehicle reduce. With the proliferation of small-scale unmanned aerial vehicles, such concerns have increased in relevance. Wing geometry deviationsmay be due to damage, poor assembly, or simplified structure and design. This is commonly seen in radio-controlled (R/C) aircraft. Weight and cost considerations result in aircraft composed largely of balsa and plywood with aMonoKote skin covering. Generally, the wing skin is not supported between the ribs or the leadingand trailing-edge spars. This naturally results in flats when the skin is attached and stressed. As a result, the airfoil design and that actually implemented on the aircraft may be significantly different. Although wing/airfoil contour issues or alterations due to effects such as battle damage [1,2] have been investigated, little information appears available on a systematic study of contour effects thatmay result fromR/C modeling techniques. Consequently, a low-speed wind-tunnel investigation has been undertaken to quantify the effect of surface flats on the behavior of a Clark-Y airfoil. Data presented include surface pressure, wake survey, integral lift and drag coefficients, and surface flow visualization.