Low-speed Wind Tunnel Tests Research Articles

デルタ形状ボルテックスジェネレーターによる後縁フラップ上の離流れ制御について

Low-speed wind tunnel tests were performed to investigate aerodynamic effects induced by delta-shaped vortex generators installed on the upper surface of a trailing-edge flap. The vortex generator was applied to control the flow field around the trailing-edge flap where the flow was separated from the hinge line of the trailing-edge flap. The test results showed that the vortex generators increase the lift coefficient and the lift-to-drag ratio when the trailing-edge flap deflects to 30degrees. The leading-edge separation vortices formed from the delta-shaped vortex generators suppressed the flow separation on the trailing-edge flap. The height of the vortex generator geometrically changes depending on the trailing-edge flap deflection angles. Therefore, when the trailing-edge flap is not deflected such as cruise flight condition where the flow field is dominated by the attached flow, the vortex generator does not impose a penalty on the aerodynamic performance.

Canard flow improvement in a split canard configuration

Extensive low-speed wind-tunnel tests are performed to study the flow field structure over a dual-surface canard, known as split canard, in comparison to the conventional configurations. Surface pressure for both steady deflections and unsteady oscillations of the canard are measured and compared for both canard-alone and split-canard cases. The split canard shows a superior advantage at high angles of attack, where a delay in the vortex breakdown phenomena on the canard surface is observed. For the split-canard configuration, the downwash of the front canard reduces the effective angle of attack at the inboard section of the rear element which postpones formation of the leading-edge vortex. Furthermore, a region of considerably high suction was observed at front portion of the rear canard when compared with the isolated canard case. This can be thought of as the main mechanism of performance enhancement in split canards comparing to the conventional configurations.

Autorotation dynamics of a low aspect-ratio rectangular prism

This paper presents two previously unreported aspects of the autorotation dynamics of low aspect ratio rectangular prisms, observed during an experimental study of the dynamics of helicopter underslung loads. Low-speed wind tunnel tests of a simplified container model free to rotate on a fixed axis demonstrated (a) that autorotation rate can lock-in to a structural mode and (b) that static hysteresis in autorotation rate can occur at low speeds. Autorotation lock-in behaves in a similar manner to vortex-shedding lock-in, suggesting that a similar feedback flow process between vortex wake dynamics and body motion is operating, and may provide a partial explanation for the complex changes in behaviour of rotating slung loads at high airspeeds. Static hysteresis at low speeds results in a bifurcation diagram for autorotation which is similar to that for cross-wind galloping of a square prism, including the effects of friction and inertia. The similarity in bifurcation behaviour seems likely to indicate similar dynamics rather than flow physics, suggesting that it may be possible to apply techniques developed to model the effect of non-linear damping characteristics in galloping to the modelling of autorotation.

Numerical Study of Effects of Mach number on Aerodynamic Performance of Large Enthalpy Drop Stationary Cascade

Based on the method to change blade loading type along blade height, that is, applying aft-loading at both end zones of cascade while applying fore-loading in the mid zone of cascade, HTC (Harbin Turbine Company) designed a twisted and bowed stationary cascade with low aspect ratio and large enthalpy drop. To verify the aerodynamic performance of such cascade, firstly, low-speed wind tunnel tests were conducted to validate the calculation results of commercial software CFX, and then numerical simulations were made for the aerodynamic performance of the cascade at different Mach numbers. The simulation results show that the large enthalpy drop stationary cascade designed by HTC can offer good aerodynamic performance while keeping its high-load characteristics in the change range of outlet Mach number as stated in this paper.

Multidisciplinary analysis of CROR propulsion systems: DLR activities in the JTI SFWA project

In the frame of the EU 7th Framework Joint Technology Initiative Smart Fixed Wing Aircraft project, the DLR Institute of Aerodynamics and Flow Technology (DLR-AS) is participating as an associated partner in the Airbus-led studies of the Contra-Rotating Open Rotor (CROR) as possible powerplant for future transport aircraft. Due to significant technical challenges in terms of noise emissions, installation effects and certification that still need to be addressed for this novel propulsion system, the numerical activities require the use of sophisticated multidisciplinary analysis tools and approaches covering aerodynamics, aeroacoustics and aeroelastics. In this paper an overview of the DLR-AS work in the project is given, which covers the numerical assessment of a novel noise reduction technology, an initial study of blade aeroelasticity as well as some in-depth studies on isolated and installed pusher-configuration CROR engine configurations. The first results of a validation of the numerical simulations using experimental test data that is being generated in Airbus-led low-speed wind tunnel tests are also presented.

Experimental investigation of aerodynamic interaction between tip leakage flow and spontaneous tip injection flow using 2D-PIV

This paper aims to investigate the flow field characteristics of tip leakage flow in a linear cascade with single-hole spontaneous tip injection (STI) introduced as a passive control mechanism. A small-scale low-speed wind tunnel test rig was developed and the planar flow field adjacent to the injection hole was measured under different operating conditions using 2D-PIV technique. This paper presented the detailed aerodynamic interaction between the STI and the tip leakage flow (TLF) under the both laminar and turbulent flow conditions in the tip clearance. Based on the measurement results, we found that the maximum suppression effect occurred in the 3m/s case in the range of test velocity, and the suppression mechanism of spontaneous tip injection on tip leakage flow were illuminated preliminarily. The vortical structure similar to the Karman vortex street (KVS) appearing in the wake of tip injection flow was noticed and discussed briefly in this paper.

Study on gust alleviation control and wind tunnel test

Aircraft are inevitably affected by gust during flight, which disturbs the regular operations of pilots and worsens the ride quality. In more grievous cases, flight mission cannot be completed and the flight safety may be disserved. In order to improve the ride quality and the fatigue life of the plane structure under the affect of gust, it is necessary to explore and validate the gust alleviation schemes. Through the low-speed wind tunnel test, the gust alleviation active control technology applied to elastic aircraft is studied. For a large-type passenger plane configuration with high aspect ratio wing, a test system was designed and three gust alleviation control schemes with PID controllers were proposed. Finally the gust alleviation control low-speed wind tunnel test was carried out in the FD-09 wind tunnel. Test results showed that at certain speed and gust frequency, all of the 3 control schemes can alleviate the acceleration at fuselage and wing-tip to a certain extent, as well as the bending moment of wing-root. The gust alleviation control scheme, which uses aileron, elevator and canard as control surfaces synthetically, gives the most satisfying gust alleviation effect.

1197 ON THE MECHANISM OF BLUFF BODY FLOW CONTROL BY PULSED PLASMA ACTUATOR

To clarify the flow mechanism of the separation control on circular cylinder when pulsed plasma actuator is applied, the characteristics of the induced jet from the pulsed plasma actuator was examined from the results of jet thrust measurement and high-speed schlieren flow visualization. The effect of the frequency of pulsed plasma actuator on the flow separation on a circular cylinder model is discussed in the viewpoint if aerodynamic force and the flow field measured with time-resolved PIV at the low speed wind tunnel test. As a result, pulse frequency dependency of the strength of the induced jet is clarified and their direct effect in the separation control performance is observed.

B02 柔軟構造エアロシェルの構造強度評価:大型低速風洞試験と数値シミュレーション(構造・機構(1))

B02 柔軟構造エアロシェルの構造強度評価:大型低速風洞試験と数値シミュレーション(構造・機構(1))

P01 柔軟構造エアロシェルの構造強度評価:大型低速風洞試験と数値シミュレーション(ALSSポスターセッション/アピールタイム(1))

P01 柔軟構造エアロシェルの構造強度評価:大型低速風洞試験と数値シミュレーション(ALSSポスターセッション/アピールタイム(1))

Low-speed Wind-tunnel Test Results of a BWB-UCAV Model

Wind-tunnel test results of a BWB-UCAV model which was modified slightly from UCAV 1303 at a free stream speed of 50m/s at various angles of attack and yaw angles are presented in the present paper. The six-component force and moment coefficients were measured by using internal balance. Well known pitch-break phenomenon was identified to occur at a rather low angle of attack. Yawing and rolling moment coefficients from the measurements data also were found to exhibit very irregular pitch-break type behavior at non-zero yaw angles. To elucidate some aerodynamic flow structures, surface oil flow visualization and PSP measurements were also carried out.

Wind Tunnel Experimental Study of Wind Turbine Airfoil Aerodynamic Characteristics

High lift and low drag are desirable for wind turbine blade airfoils. The performance of a high lift airfoil at high Reynolds number (Re) for large wind turbine blades is different from that at low Re number for small wind turbine blades. This paper investigates the performance of a high lift airfoil DU93-W-210 at high Re number in low Re number flows through wind tunnel testing. A series of low speed wind tunnel tests were conducted in a subsonic low turbulence closed return wind tunnel at the Re number from 2×105to 5×105. The results show that the maximum lift, minimum drag and stall angle differ at different Re numbers. Prior to the onset of stall, the lift coefficient increases linearly and the slope of the lift coefficient curve is larger at a higher Re number, the drag coefficient goes up gradually as angle of attack increases for these low Re numbers, meanwhile the stall angle moves from 14° to 12° while the Re number changes from 2×105to 5×105.

F051001 感圧塗料による非定常計測

Pressure-sensitive paint (PSP) is an optical pressure measurement technique based on oxygen quenching of photo-excited luminophores. Applications of PSP to unsteady low-speed flow are anticipated in many areas, but the limitation of PSP accuracy makes them difficult. A recent advancement in paint formulation, optical equipment and image processing techniques enables us of acquiring quantitative unsteady-pressure field using PSP. In this paper, two different approaches to this problem, the modified phase-lock method and the conditional image-averaging method are introduced and the results of low-speed wind-tunnel tests are present. These advanced techniques can be applied to unsteady flow even with naturally-disturbed components and their accuracy reaches to Δp_<rms> of 16 Pa.

Design of a smart leading edge device for low speed wind tunnel tests in the European project SADE

PurposeThe purpose of this paper is to describe the pre‐design and sizing of a smart leading edge section which is developed in the project SADE (Smart High Lift Devices for Next Generation Wings), which is part of the seventh framework program of the EU.Design/methodology/approachThe development of morphing technologies in SADE concentrates on the leading and trailing edge high‐lift devices. At the leading edge a smart gap and step‐less droop nose device is developed. For the landing flap a smart trailing edge of the flap is in the focus of the research activities. The main path in SADE follows the development of the leading edge section and the subsequent wind tunnel testing of a five meter span full‐scale section with a chord length of three meters in the wind tunnel T‐101 at the Russian central aero‐hydrodynamic institute (TsAGI) in Moscow.FindingsThe presented paper gives an overview over the desired performance and requirements of a smart leading edge device, its aerodynamic design for the wind tunnel tests and the structural pre‐design and sizing of the full‐scale leading edge section which will be tested in the wind tunnel.Originality/valueSADE aims at a major step forward in the development and evaluation of the potential of morphing airframe technologies.

Integrated Experimental-Numerical Analysis of High-Agility Aircraft Wake Vortex Evolution

The presented investigation includes a combined experimental–numerical approach to quantify the wake vortex system of a high-agility aircraft from the near field up to the far field. Detailed near-field data are obtained by lowspeed wind-tunnel tests on a delta-canard configuration of 1:15 scale. The measurements are performed at several angles of attack applying advanced hot-wire anemometry. For a wake distance of up to 16 wing spans, mean and turbulentvelocity fieldsaremeasured.Theupstreamdataareusedtoinitializeimplicitlarge-eddysimulationsaimed tocomputethevelocity fieldsofthewakevortexsystemoverawakedistanceofupto50spans.Here,avalidationcase is shown comparing measured and calculated wake data over a distance from 4 to 16 spans, with the implicit largeeddy simulations initialized by the measured quantities at a position of two wing spans. Compared with the experimental data,the numericalresults showthe expectedlateral andvertical movementof thewakevortexsystem due to the interaction of the single vortices. The distributions of axial vorticity, crossflow velocities, and turbulence intensities match well with the experimental data. Inaddition, the dissipation process can be observed, resulting in a reduction of circulation. In the context of this study, the measured and computed velocity fields will be used to determine unsteady aerodynamic loads acting on a fighter aircraft encountering the wake. This is of great importance as wake induction may result in critical structural dynamic loads.

Effect of surface contamination on the performance of a section of a wind turbine blade

A series of low speed wind tunnel tests were conducted on a section of a 660 kW wind turbine blade to examine the effects of distributed surface contamination on its performance characteristics. The selected airfoil was tested with a clean surface, two types of zigzag roughness, strip tape roughness and distributed contamination roughness. The straight and zigzag leading edge roughness models simplify the contamination results in an early turbulence transition. In this study, surface contamination was simulated by applying 0.5 mm height roughness over the entire upper surface of the airfoil. The distribution density varied from the leading edge to the trailing edge of the model. Our data show that this particular airfoil was very sensitive to surface contamination and its maximum lift coefficient decreased up to 35%, while the stall angle of attack increased slightly. The surface contamination, however, caused very smooth stall characteristics and less lift drop in the post stall region. In contrast to the clean model, the maximum lift coefficient of the roughened airfoil increased with Reynolds number. The effects of zigzag roughness and strip tape roughness were less than that of the distributed contamination roughness.

Wave space array methods for aeroacoustic testing.

Phased array beamforming is commonly applied to assess the spatial distribution of noise sources in aeroacoustic wind tunnel testing, generally with planar microphone arrays. As classically applied with a conventional beamforming algorithm, results can suffer contamination due to cross‐flow over the array face in the wind tunnel test environment. When the cross‐flow fluctuations are statistically independent from microphone‐to‐microphone, diagonal removal can be applied to the cross‐spectral matrix to negate this contamination. However, when these fluctuations are correlated, diagonal removal fails to recover the acoustic field of interest. As has been previously demonstrated, the wave space representation of an observed pressure field readily separates cross‐flow hydrodynamic fluctuations from the observed acoustic field, when applied to low speed wind tunnel tests. The authors build on existing research to construct beamforming methods in wave space to leverage this separability. The implications of aer...

Validation Testing of Drift Reduction Technology Testing Protocol

Abstract A number of pesticide application technologies offer the potential to reduce spray drift from pesticide applications. However, limited information exists on the effectiveness of these technologies in reducing spray drift. Working with a stakeholder technical panel under EPA’s Environmental Technology Council, the Office of Pesticide Programs in EPA has developed and is in the process of validating a testing protocol to verify the effectiveness of drift reduction technologies (DRTs). The DRT testing protocol was adapted from standard test methods and regulatory methods used in other countries and describes the testing approach that will be used to generate high-quality, peer-reviewed data for DRTs, including test design and quality assurance aspects. Both low-speed and high-speed wind tunnel tests were completed using a reference nozzle and two test nozzles to evaluate the performance of the generic DRT testing protocol. By Summer 2010, EPA anticipates to finalize this testing protocol based on the test results performed by EPA and other stakeholders. As a next step, EPA intends to encourage equipment manufacturers to voluntarily use the protocol for testing their equipment. Tested technologies that are proven to significantly reduce spray drift may be considered for addition to pesticide product labels by pesticide registrants and by EPA in its risk assessment and management decisions for the registration of new pesticide and uses and registration review (reevaluation) of currently registered pesticides. Pesticide product labels citing the use of DRTs could have reduced restrictions for applications, provide applicators with greater flexibility, and result in less off-target pesticide deposition. This paper will provide an update of EPA’s efforts to validate the DRT testing protocol and discuss future plans for using a validated protocol in evaluating DRTs in an effort to reduce load from unintended spray drift of pesticides in the environment.

Model Aerodynamic Tests with a Wire-driven Parallel Suspension System in Low-speed Wind Tunnel

Owing to the advantages of wire-driven parallel manipulator, a new wire-driven parallel suspension system for airplane model in low-speed wind tunnel is constructed, and the methods to measure and calculate the aerodynamic parameters of the airplane model are studied. In detail, a static model of the wire-driven parallel suspension is analyzed, a mathematical model for describing the aerodynamic loads exerted on the scale model is constructed and a calculation method for obtaining the aerodynamic parameters of the model by measuring the tension of wires is presented. Moreover, the measurement system for wire tension and its corresponding data acquisition system are designed and built. Thereafter, the wire-driven parallel suspension system is placed in an open return circuit low-speed wind tunnel for wind tunnel tests to acquire data of each wire tension when the airplane model is at different attitudes and different wind speeds. A group of curves about the parameters for aerodynamic load exerted on the airplane model are obtained at different wind speeds after the acquired data are analyzed. The research results validate the feasibility of using a wire-driven parallel manipulator as the suspension system for low-speed wind tunnel tests.

1501 カルマン渦が誘起する非定常圧力場の感圧塗料計測(OS15-1 先端的熱流体計測法,オーガナイズドセッション)

To understand unsteady flow phenomena around a body, it is important to measure time-resolved surface pressure distributions with high spatial resolution. Pressure Sensitive Paint (PSP) has a capability of providing high-resolution pressure images. In this study, we propose a new PSP technique to obtain time-resolved surface pressure distributions by using conditional sampling of time-series PSP images. To obtain high SNR data, the high-speed camera images are phase-averaged after image acquisition, using a simultaneously-measured pressure transducer data to detect a phase of each image. This method allows us to obtain high SNR images at arbitrary phase of the periodic phenomena using a simplify measurement system and image processing. The effectiveness of the present method was evaluated by applying it to a 3-D square cylinder in low-speed wind tunnel testing. As a result of this experiment, we could obtain time-resolved unsteady pressure images around the square cylinder caused by periodic vortex shedding.