Test Section Flow Research Articles

Measurement and Modeling of Subscale Open-Return Unsteady Wind-Tunnel Behavior

Unsteady-flow wind tunnels typically employ control louvers installed in the wind-tunnel circuit to produce rapid changes in the test-section flow velocity. For these wind tunnels, an open-return circuit is advantageous because of the lower mass of air that must be accelerated by the louver forcing. However, in addition to inertial effects, the wind-tunnel behavior is also affected by the interaction of the pressure disturbances from the louvers and their reflection from the open boundary conditions of the wind tunnel, resulting in a windspeed response that is nonintuitively related to the louver motion. In this paper, an experimental investigation into the unsteady behavior of a model-scale, open-return wind tunnel is described. An incompressible method of characteristics model for the wind tunnel is shown to successfully predict the wind-tunnel dynamic behavior, and an approach to produce controlled windspeed histories that compensates for the wind-tunnel response is demonstrated.

Design, assembly and testing of an upgraded aeroacoustics wind tunnel facility

The Aeroacoustics Laboratory in the Department of Aerospace Engineering at Penn State currently serves several areas of experimental research. Most notable in the laboratory is the Anechoic Chamber of which the Aeroacoustics Wind Tunnel is an integral part. In recent years the dominant areas of research have included model aircraft exhaust jets and model rotors for helicopter applications involving detailed noise experiments. In the jet noise area, the applications have included aircraft in both flyover and take-off configurations. In the flyover application the air flow surrounding the exhaust jet has a significant effect on the radiated noise and must be simulated to produce experimental results that will be most useful in preliminary design of noise suppression applications. The Aeroacoustics Wind Tunnel at Penn State serves the purpose for this simulation. During aircraft take-off, the aircraft airspeed is in a range exceeding 250 ft per second, or Mach number of over M = 0.22. In the years preceding 2022, the velocity of the free jet flow of the Penn State facility was limited to less than 200 ft/sec. This paper reports on a project to design upgrades to the existing wind tunnel to improve the test section flow velocity to values closer to the 250 ft/sec target. The approach began with a preliminary design of the return flow ducting to convert the open jet, open return wind tunnel to a closed return tunnel. The concept is to make use of the flow energy in the exhaust of the tunnel to boost the input energy to the inlet fan that drives the flow to the test section. An integral part of the preliminary design involved making use of an upgraded flow analysis computer code to predict the gain in test section velocity of the new facility. For the available horsepower of two fans in the facility, the configurations of the existing and upgraded wind tunnel were entered into this analysis code based on a quasi-one-dimensional formulation. The code included empirical data formulated to include the various shapes of the components of the tunnels. The relative flow velocities in each section used simple incompressible continuity to calculate all velocities in the component sections. The average dynamic pressure in each section is calculated from the flow (constant) density and the velocity squared. Each section had a non-dimensional pressure loss parameter calculated from empirical data (from the relevant literature). The basic code (using the Excel algorithms) was based on a predictor-corrector concept in which the calculation was initialized with the estimated velocity and pressure of the flow at the entrance to the test section. The loss in each following section is estimated to determine the loss in the total pressure and the cumulated loss compared to the gains made at the two fans in the circuit. The initial guess is adjusted based on the total pressure value at the end of the circuit. During the related experiments, measurements of the total and dynamic pressure were performed at several joints between sections and compared to the values predicted in the analysis code. Various settings of the horsepower of the drive fans were used and the results were compared to flow measurements for the tunnel configurations (predominantly for the open return and closed return tunnel setups available before and after the upgrade project.) Results of the analysis and experiments are presented and analyzed together with the remaining activities planned for the coming months.

A Numerical Evaluation for a Newly Designed Closed Loop Subsonic Wind Tunnel

A wind tunnel is a piece of equipment specifically designed for studying the influence of air passing over solid matters in aerodynamic research. Computational Fluid Dynamics (CFD) was used to conduct methodical research into the design and modeling of flow characteristic in a closed-loop wind tunnel. The necessary intake fan velocity was established using an analytical velocity model, and the test section's inlet conditions were produced by applying the Reynolds number equation, assuming that the Reynolds number was 500,000. Instead than using the traditional method, a full-scale CFD model of the complete wind tunnel was taken into consideration. This made it possible to improve the flow quality over the entire circuit as well as only in the test area. The test section flow quality was more impacted by upstream flow circumstances than downstream conditions, according to analysis of the guide vane designs. Therefore, careful consideration has to be done while constructing the vanes at upstream curves, especially corners that are parallel to the test section. The simulation results showed that, in the case of a fully configured wind tunnel, flow uniformity in the test section is successfully attained.

Design of an instrumentation system for assessing the acoustic attenuation performance of ducted Helmholtz resonators in the presence of grazing flow

The Helmholtz resonator (HR) has been widely used as a duct silencer to reduce low-frequency noise. However, the presence of grazing flow could influence the noise attenuation performance of the HR in ductwork systems. This study aimed to design an instrumentation system for studying the acoustic attenuation performance of ducted HRs in the presence of grazing flow. The instrumentation system includes a centrifugal fan, diffusion section, anechoic termination, flow development section, test section, and sound source. In this study, a HR as a ducted silencer was installed in the test section of the instrumentation system. Transmission loss (TL) due to the HR insertion was measured in the presence of forward and reverse grazing flows. The results showed that the instrumentation system succeeded in assessing the noise attenuation performance of the HR under a high sound pressure level and different flow rates and directions.

Investigation on multiscale features of cavitating flow in convergent-divergent test section using Eulerian–Lagrangian method

Cavitating flows in fluid machineries always present complicated phase morphologies including a wide range of interface length scales. In the present work, an Eulerian–Lagrangian cavitation model is proposed for simulating the unsteady cavitating flow and investigating the multiscale cavitating flow features in a convergent-divergent test section. Most importantly, a two-way transition algorithm is newly developed mainly based on the shape of resolved cavities and the relative size of microscale bubbles compared to the cells, for taking the transition between microscale discrete bubbles and macroscale vapor cavities into consideration. The transient flow field of the two-phase system is described by the filtered Navier–Stokes equation and the sub-grid scale model. The volume of fluid (VOF) method and a discrete bubble model (DBM) are combined for simulating resolvable water-vapor interfaces and unresolvable discrete bubbles, respectively. Applying the proposed multiscale modeling framework, the dissipated bubbles caused by the collapse of shedding cavities that are unable to be represented by the VOF method are well predicted. The results show that the VOF-DBM model is less sensitive to the mesh resolution compared to the VOF method and it is found the dissipated bubbles are transporting around the vortex core region. Detailed bubble dynamics including DBM to VOF and VOF to DBM transitions and the interaction between macroscale cavities and microscale bubbles are well presented, indicating that the proposed VOF-DBM model is a promising approach to reveal the multiscale cavitation characteristics within limited computing resources.

Effect of mass flow rate on bubble size distribution in boiling flow in temperature-controlled annular test section

Subcooled flow boiling experiments were performed in an annular horizontal channel with inner diameter of 12 mm and the gap of 2 mm. The annular channel is designed as a double-pipe heat exchanger, where the inner tube of the channel is heated by a water flow, providing a temperature-controlled boiling surface. The influence of mass flow rate of the working fluid R245fa on flow boiling patterns and heat transfer has been studied. Subcooled flow boiling patterns were recorded with a high-speed camera. The recorded images of the flow patterns were then further processed to determine the bubble size distributions, characterized as distributions of the void (vapour) volume given per bubble size. The observed bubble size distributions followed two distinct distribution functions: the Rayleigh distribution at larger and bimodal distribution at smaller mass flow rates. This indicates the existence of two distinct boiling flow regimes at different mass flow rates. The heat flux was estimated by local temperature measurements with thermocouples positioned along the boiling surface and in the heating water. The heat flux increased moderately with increasing mass flow rate, apparently without disruption at the observed change in the flow regime. On the contrary, the total void volume in the observed part of the test section is declining moderately with increased refrigerant mass flow rate, which, in this mode of operation of the test section, acts as a prevailing mechanism. The experimental setup, methods of experimental analysis and the results are presented and discussed.

The axial fan design and commissioning test with nonuniform inlet flow

According to the two-dimensional flow theory of the axial fan rotor blades and the aerodynamic characteristics of the low speed wind tunnel, combined with the fan aerodynamic efficiency and wind tunnel pressure loss coefficient, a new equation which points out the inherent relationship of the fan blade setting angle, fan rotating speed and flow rate in wind tunnel circuit is derived. So a new method for fan rotor blade setting angle adjustment to satisfy the fan performance at off-design point by getting the test results of fan operating parameters but without the fan total pressure rise in the low speed wind tunnel is developed. Following the new method, the fan rotor blade setting angle adjusting value was provided directly only with the fan rotating speed and flow velocity in the wind tunnel test section, the adjusting target was achieved successfully by the new blade setting angle, the cost of the wind tunnel commissioning test were saved. The test results show that, after increasing the fan rotor blade setting angle by 4.5 degrees, when the flow velocity in the wind tunnel test section reaches 60m/s, the fan rotating speed is 570rpm, the deviation from the predicted fan rotating speed value of 575rpm is 0.9%. For the same test section flow velocity, the predicted value and the real value of the fan rotating speed are in good agreement, it proves that this method is reliable and accurate in practical application.

Supersonic jet by blast wave focusing

A supersonic jet of Mach number M = 4.5 in air is produced experimentally at the apex of a miniature 150 × 50 × 5 mm converging section with a 2 × 5 mm opening by the principle of blast wave amplification through focusing. An initial plane blast wave of M = 2.4 in the convergence section is generated by the exploding wire technique. The profile of the convergence section is specially tailored to smoothly transform a plane blast wave into a perfectly cylindrical arc, imploding at the apex of the section. The cylindrical form of the imploding shock delivers maximum shock amplification in the two-dimensional test section and maximum subsequent jet flow velocity behind the shock front. Blast wave propagation in the convergence chamber as well as jet generation through a 2 mm opening at the apex into the adjacent exhaust chamber is optically captured by a high-speed camera using the shadowgraph method. Visualizing the flow provided a distinct advantage not only for obtaining detailed information on the flow characteristics but also for validating the numerical scheme which further enhanced the analysis. Experimental images together with the numerical analysis deliver detailed information on the blast wave propagation and focusing as well as subsequent jet initiation and development. One of the main advantages of the described method apart from being simple and robust is the effective focusing of low initial input energy levels of just around 500 Joules, resulting in production of supersonic jets in a small confined chamber.

Two-Phase Flow Regimes and Heat Transfer Coefficients With R245fa in Manifolded-Microgap Channels

Manifold microchannels have shown high performance in embedded two-phase cooling of high heat flux electronics, demonstrating several examples of heat dissipation of 1 kW from 1-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> chips, with low pumping power requirements. The heat transfer coefficients (HTCs) in previous studies of chip-scale manifold-microchannel coolers exhibited a peak at relatively low quality (about 0.2–0.4) and steeply declined thereafter with increasing quality. However, manifold microchannels—arrays of manifolded-microgap channels—are a more complex geometry than traditional, straight, and circular channels and therefore generate more complex two-phase flow phenomena, which influences the resulting heat transfer performance. To better characterize the flow and heat transfer in such channels, in this study, the fluid flow and wall heat transfer in a visualization test section was imaged with a high-speed optical camera and thermography. R245fa served as the working fluid due to its low-pressure operation (approximately 1.8 atm at 30 °C) and excellent thermal properties, including high latent heat, high specific heat, and high thermal conductivity. The results are reported in terms of the channel outlet flow regime and HTCs under varying heat fluxes and mass fluxes with two manifold designs. The flow regimes and HTCs are compared with well-regarded predictive relations developed for more traditional channel geometries. The emergence of intermittent, and then persistent, dryout was associated with intermittent rivulet flow at the channel outlet and was observed to cause declining average wall HTCs, even while high HTCs occurred at the consistently wetted inlet region.

Unsteady Propagation and Mean Corrections in Open-Jet and Kevlar® Wind Tunnels

Two types of aeroacoustic wind-tunnel test section configurations have been tested in the NASA Langley Quiet Flow Facility. The first is a more traditional open-jet configuration, where test section flow passes unbounded through the facility anechoic chamber. The second is a Kevlar® panel configuration, where a tensioned Kevlar sheet constrains the test section flow from the facility anechoic chamber. For both configurations, acoustic instrumentation is in the surrounding quiescent space. Both configurations are evaluated with a laser-based pulsed acoustic source, which provides unique capability for assessing the facility unsteady acoustic propagation characteristics. Metrics based on the wander and spread of the pulses are evaluated, and show that measurements using Kevlar walls experience dramatically reduced unsteady effects when compared to the open-jet configuration. This leads to a corresponding improvement in coherence between microphones with the Kevlar configuration, by reducing the variation in magnitude and phase differences between channels. Magnitude corrections for propagation through Kevlar as compared to open-jet propagation are calculated. Although limitations in the experimental setup make quantitative analysis difficult, qualitative analysis shows Kevlar magnitude corrections similar to those determined in previous literature. Directivity effects beyond those already present for open-jet configurations are minimal. When compared with the open-jet configuration, the background noise produced by the Kevlar is found to be its one drawback, showing significantly greater levels at high frequencies.

Studies on Key Effect Factors of Natural Circulation Characteristics for Advanced PWR Reactor Cavity Flooding System

In order to enhance the ability of severe accident mitigation for Pressurised Water Reactor (PWR), different kinds of severe accident mitigation strategies have been proposed. In-Vessel Retention (IVR) is one of the important severe accident management means by External Reactor Vessel Cooling. Reactor cavity would be submerged to cool the molten corium when a severe accident happens. The success criterion of IVR strategy is that the heat flux which transfers from the corium pool must be lower than the local critical heat flux (CHF) of the reactor pressure vessel (RPV) outside wall and the residual thickness of the RPV wall can maintain the integrity. The residual thickness of RPV is determined by the heat flux transfer from the corium pool and the cooling capability of outer wall of the RPV. There are various factors which would influence the CHF and the cooling capability of outer wall of the RPV. In order to verify the optimized design which is beneficial to the heat transfer and the natural circulation outside the actual reactor vessel, a large-scale Reactor Vessel External Cooling Test (REVECT) facility has been built. A large number of sensitivity tests were carried out, to study how these sensitivity factors affect CHF value and natural circulation. Based on the test results, the structure of the test section flow channel has an obvious effect on the CHF distribution. The flow channel optimized can effectively enhance the CHF value, especially to enhance the CHF value near the “heat focus” region of the molten pool. The water level in the reactor pit has also a great impact on the natural circulation flow. Although natural circulation can be maintained with a low water level, it will lead to a decrease of the cooling capacity. Meanwhile, some noteworthy test phenomena have been found, which are also essential for the design of the reactor pit flooding system.

Design and qualification of an unsteady low-speed wind tunnel with an upstream louver system

The design and qualification of a longitudinal gust generator in a low-speed, blow-down, open-return wind tunnel was conducted. Flow-impeding louvers were used to rapidly change the blockage ratio at the inlet, effectively reducing test section flow speeds up to $$60\%$$ and $$52\%$$ for the closed and open test section configurations of the wind tunnel, respectively. The wind tunnel responds more quickly for higher fan speeds, shorter tunnel lengths, and during louver closing motions (deceleration). A mathematical model developed to predict the wind tunnel’s response shows these same trends and agrees with the experimental data to within 0.03 in amplitude ratio and $$4.3^\circ$$ in phase lag, for all cases studied. Comparison of the closed to open test section configurations reveals that flow disturbances propagate nearly instantaneously, or in a globally unsteady manner, within the closed configuration, while they convect at speeds similar to that of the mean flow when testing in the open configuration.

Effect of asymmetric airflow on liquid film behavior and emergency core coolant bypass in the downcomer geometry of a nuclear reactor pressure vessel

In this study, experimental work was carried out using a 1/10 reduced-scale downcomer of a nuclear reactor pressure vessel to examine the liquid film behavior under emergency core coolant (ECC) bypass conditions. It is caused by the interaction between the transverse gas flow and the falling liquid film. The experiments were conducted considering the asymmetric gas velocity inside the downcomer. An air–water mixture was used as the working fluid in the experiment, forming a complex liquid film flow in the annular test section of the downcomer. To measure the local liquid film thickness, an electrical conductance sensor fabricated on a flexible printed circuit board was applied. The effect of the asymmetric airflow on the liquid film behavior was investigated using the liquid film thickness measurements. Results showed that the asymmetry influences the distribution of the liquid film; the larger the asymmetry, the closer is the liquid film is to the break with the same gas outlet velocity. It influences the trend of the ECC bypass fraction with respect to the gas velocity. The present study provides detailed understanding of the ECC bypass phenomenon under asymmetric airflow conditions; this enables determining how the liquid film behavior is changed by the gas flow and how it affects the ECC bypass.

Spectral feedback control of turbulent spectra in a wind tunnel

Longitudinal flow velocity control was conducted in the Andrew Fejer Unsteady Wind Tunnel to produce velocity spectra that emulate atmospheric turbulence. A louver mechanism placed at the downstream end of the test section determines the resistance to the flow by varying the louver deflection angle, and hence changes the test-section velocity. The test-section flow velocity was decomposed into an adjustable mean flow $$u_0$$ and a fluctuation $$u'$$ , which were respectively controlled by the mean louver deflection angle and the oscillations of the louvers about that mean angle. A linear interpolation of the static map of the test-section flow speed with respect to the louver deflection angle was used as an open-loop controller for the longitudinal flow velocity. A feedback loop that measures the velocity spectrum over a short time interval constructed a closed-loop controller, which controls the mean flow speed as well as the amplitudes over a range of individual frequencies within the fluctuation spectrum. The spectral feedback approach was tested by generating the longitudinal velocity components of von Karman turbulence spectra and Dryden turbulence spectra. The controller proved to be capable of controlling the gust frequency with a bandwidth of 7 Hz given the current hardware configuration.

A New Method for Adjusting Setting Angle of Rotor Blade for Axial Fan in Wind Tunnel

Combining the fan aerodynamic efficiency with the wind tunnel pressure loss coefficient, a new equation which points out the inherent relationship of the fan blade setting angle, fan rotating speed and gas flow rate in wind tunnel circuit is derived according to the two-dimensional flow theory of the axial fan rotor blades and the aerodynamic characteristics of the low speed wind tunnel. So a new method for setting angle adjustment of fan rotor blade to satisfy the fan performance at off-design point by getting the test results of fan operation parameters but without the fan total pressure rise in the low speed wind tunnel is developed. Flowing the new method, the setting angle adjusting value of fan rotor blade was provided only with the fan rotating speed and flow velocity in the test section of a low speed wind tunnel directly before the fan setting angle altered, the adjusting target was achieved by the new blade setting angle successfully and the time and cost of the wind tunnel commissioning test were saved. The test results show that, after increasing the fan rotor blade setting angle by 4.5 degrees, when the flow velocity in the wind tunnel test section reaches 60 m/s, the fan rotating speed is 570 r/min, the deviation from the predicted fan rotating speed value of 575 r/min is 0.9%. For the same test section flow velocity, the predicted value of the fan rotating speed is in a good agreement with the real value, it proves that this method is reliable and accurate in practical application.

Experimental investigation of the effect of drill pipe rotation on improving hole cleaning using water-based mud enriched with polypropylene beads in vertical and horizontal wellbores

Field experience has shown that the inefficient transport of small cuttings is a main factor contributing to excessive drag and torque during the drilling of a deviated hole; however, very little is known about the transport behavior of small cuttings. This experimental study investigates the effect of different polypropylene bead concentrations in water-based mud (WBM) on hole cleaning, along with the effects of cutting size, drill pipe rotation, and hole inclination angle. A total of 160 runs were performed using an experimental rig consisting of a 13 ft (3.96 m) long casing with a 2 in (50.8 mm) Inner Diameter (ID) and a rotary inner pipe with a 0.8 in (20 mm) Outer Diameter (OD). Four cutting size ranges, namely, 0.5–1.0 mm, 1.0–1.4 mm, 1.4–1.7 mm, and 1.7–2.0 mm, with a density of 2400 kg/m3 were tested in WBM with varying polypropylene bead concentrations ranging from 0 to 8 ppb. The concentric annulus flow test section was changed to vertical and horizontal angles with pipe rotation from 0 to 150 rpm. The mud density and viscosity were maintained at 10 ppg and 16 cp, respectively, under a flow velocity of 3.48 m/s (Reynolds number of 6620). The results indicate that smaller cuttings are easier to transport at all pipe rotations and polypropylene bead concentrations in both vertical and horizontal holes. The optimal pipe rotational speed was found to be 60 rpm. In this study, polypropylene beads undeniably enhanced the mud carrying capacity by significantly increasing the cutting transport ratio (CTR) by up to 16.57% in vertical holes and 15.73% in horizontal holes.

Measurement uncertainty and quenching phenomena in uniform heating rod bundle CHF tests

The uniform heated rod bundle Critical Heating Flux (CHF) tests have been often conducted as a part of mixing vane performance evaluation processes. Presently, several commercial CHF correlations were developed based on a large amount of rod bundle CHF data using axial uniformly heated rod bundles. With a uniformly heated test section, majority of CHF events are dominated by dry-out mechanism under high quality, high void fraction local conditions. Considering the inverse proportional relationship between the quality and CHF, for an axially uniformly heated test section, the CHF events should occur near the end of heating length (EOHL) where the void fraction/quality is the highest. However, the upstream shift of CHF location is often observed in the uniform heating tests, sometime as much as 250 mm or higher upstream from the EOHL.In the past, without any sufficient convincing proof, long dryout areas as well as “unknown” “mysteries” mixing effects from the mixing vane grid were often considered as the contributing factors for this type of upstream shift. Based on further and detailed examination, this paper offer analysis and evidence to demonstrate another most plausible explanation, exit quenching effect, which ultimately concludes that rod bundle CHF using uniform heated rods could have data with huge measurement uncertainty and as much as over 30% of non-conservatism due to heat lose and quenching effects at the exit of the heated length. The quenching effect at the exit of heater length is mainly due to reflood phenomena generated between the high void/low flow test section exit region and the relatively cold single phase coolant immediately above in the top plenum resulting from either excessive heat loss or operating transient condition.In this paper, system code and CFD modeling were utilized to simulate the quenching phenomena in both steady state and transient conditions. The significant void fraction drop near the exit of the test section due to quenching were clearly observed in these simulations and also evidenced by the various degrees of coloration of the heaters surface in the experiment. This exit reflood quenching phenomena may change the CHF location, suppress boiling, cool down the heated surface, and eventually lead to non-conservative high CHF values. Based on this analysis and experimental observation, it is concluded that the CHF correlations developed based on these type of data are potentially non-conservative in various degrees pending on local thermal-hydraulic conditions, which should be taken into consideration for their applications, especially for safety analysis in nuclear reactor.

Aeroacoustic wind tunnel design

Further progress in airframe noise research including noise prediction and noise reduction solutions depends on the availability of aeroacoustic wind tunnel test facilities with superior aerodynamic and acoustic quality. The demand for aeroacoustic wind tunnels with extremely low background noise and pressure fluctuations, yet with a relevant test section cross-section area and flow velocity, increased significantly over the last decade. In the future, this demand will continue to grow to cope with the challenging noise reduction objectives for aviation noise defined for the years to come. The present text is focused on the state-of-the-art aeroacoustic wind tunnels available today and their design. The design guidelines discussed here assume a classic aerodynamic wind tunnel as a baseline. Therefore, the present text is addressed to both those who are interested in the design of a completely new aeroacoustic wind tunnel as well as those interested in the acoustic upgrade of an existing aerodynamic wind tunnel. As a direct consequence of the multi-disciplinary nature of this complex task, and the multitude of solutions and design tools that are required to complete it, the approach followed here subdivides the design of the aeroacoustic wind tunnel into four main sections: wind tunnel airline circuit (includes the first and second airline cross legs), drive unit and anechoic plenum. While the design approach for the airline circuit and the drive unit is strongly based on coupled numerical solutions of CFD and acoustic solvers, the design of the acoustic plenum gives more emphasis to in situ observations and to experimental results. The main sections of the aeroacoustic wind tunnel and their best design are discussed separately in this contribution.

SIMULATION OF 2D FLOW AROUND OF AIRFOILS AT LOW-SPEED WIND TUNNEL WITH OPEN JET TEST-SECTION

At present, there is a great interest in the development of new airfoils for wind turbines and high-lift wings of unmanned aerial vehicles (UAV). The requirements for such airfoils differ from conventional aircraft airfoils, because of structural reasons and extreme operating conditions. So, wind turbine airfoils operate frequently under fully separated flow when stall is used for power regulation at high wind speeds. At the same time design of airfoils for wings UAV poses the problem of availability of high-lift at low Reynolds number. Modern airfoils are to a large extent developed from numerical methods. However, the complex flow conditions such as separation at high angles of attack, laminar separation bubbles and the transition from laminar to turbulent flow are difficult to predict accurately. Hence, testing of airfoils at a two-dimensional condition is an important phase in airfoil design. The development and validation of a 2D testing facility for investigation of single and multi-element airfoils in the wind tunnel Т-102 with open test section are considered in this article. T-102 is a continuous-operation, closed-layout wind tunnel with two reverse channels. The test section has an elliptical cross-section of 4 ×2,33 m and a length of 4 m. Two big flat panels of the L × H=3 ×3,9 m size installed upright on balance frame aligned with the free stream are used for simulating two-dimensional flow in the tunnel test section. The airfoil section in the layout of a rectangular wing is mounted horizontally between flat panels with minimum gaps to ensure 2D flow conditions. The aerodynamic forces and pitch moment acting on the model were measured by wind tunnel balance. To determine boundary corrections for a new test section of wind tunnel, the experimental investigation of three geometrically similar models has been executed. The use of boundary corrections has provided good correlation of the test data of airfoil NACA 6712 with the results obtained from the wind tunnel except for lift and drag coefficient values at high angles of attack.

Dynamic Behavior and Gust Simulation in an Unsteady Flow Wind Tunnel

Rapid oscillations of test-section flow velocity can be generated in a wind tunnel using flow-control louvers installed in the wind-tunnel circuit; however, control of the test-section velocity must still account for the dynamic behavior of the wind tunnel itself. In this paper, the dynamic behavior of a low-speed closed-circuit wind tunnel in response to dynamic louver excitation is examined using an experimentally validated method-of-characteristics modeling approach. The model is used to develop and test a method of controlling the louver motions to simulate longitudinal gusts with a von Kármán gust spectrum for length scales from 0.1 to 10 m. Results showing improvement of the wind-tunnel dynamic behavior using a Helmholtz resonator are also presented.