High-speed Wind Tunnel Research Articles

Turbine Cascades of Last Stage Blades for Wide Range of Operating Conditions

Recent trends in the electric energy market such as biomass, waste incineration or combined cycle power plants require innovative solutions in steam turbine design. Variable operating conditions cause significant changes in flow field surrounding the steam turbine last stage blades. Therefore, the enlargement of operating range for last stage blades presents new challenges in design of turbine cascades. Several turbine cascades were designed and analyzed by commercial and in-house software of CTU Prague. Selected profiles were experimentally validated in the high-speed wind tunnel for 2D cascade measurements of the Institute of Thermomechanics of the Czech Academy of Sciences which is equipped by an adjustable supersonic inlet nozzle, perforated inserts at side walls and adjustable perforated tailboard. Comparisons are presented of numerical results with optical and pneumatic measurements for a wide range of inlet and outlet Mach numbers for optimized hub and tip profile cascades.

Dynamic Stability Assessment in a High Speed Wind Tunnel

The Clean Space initiatives provide a challenge for engineers at INCAS, Romania's National Institute for Aerospace Research “Elie Carafoli”, in Bucharest

Computational fluid dynamics analysis of hand-cycle aerodynamics with static wheels: Sensitivity analyses and impact of wheel selection

Aerodynamics research in cycling has underpinned innovative bicycle design, new refined riding positions and optimised rider apparel. There has been a rise in the level of aerodynamics research focused on cycling since the turn of the millennium, enabled by significant increases in computational power and the availability of software/hardware. However, cycling research has not yet fully embraced para-cycling, with limited studies conducted on the aerodynamic performance of hand-cyclists and other para-cyclists. Wind tunnel experiments and computational fluid dynamics simulations were conducted in this research for the analysis of hand-cycling aerodynamics, focused on competitive H1–H4 category hand-cyclists. A quarter-scale representative geometry of a hand-cyclist was used in high-speed wind tunnel experiments. The accuracy of the simulations performed with the three-dimensional Reynolds-averaged Navier–Stokes equations was found to be dependent on the turbulence model choice and near-wall grid resolution. Computational fluid dynamics simulations predicted the magnitude of the drag and lateral forces to an accuracy of 2.5% using the shear stress transport [Formula: see text] turbulence model. This study also presents the impact of wheel diameter and disc wheels on hand-cycling aerodynamics via computational fluid dynamics simulations, providing a deeper understanding of the aerodynamic characteristics unique to the hand-cycling discipline in the sport of competitive cycling. Drag reductions of up to 8.9% were found when utilising 20-inch diameter spoked wheels, opposed to the 26-inch wheels. Variations in wheel diameter between the front and rear wheels were found to have a significant impact on the CDA in part through altering the pitch angle of the hand-cycle.

ОСОБЛИВОСТІ ЗАБЕЗПЕЧЕННЯ АЕРОДИНАМІЧНИХ ХАРАКТЕРИСТИК РЕГІОНАЛЬНОГО ПАСАЖИРСЬКОГО ЛІТАКА

Principal results of the computational and research work performed during development of a regional passenger aircraft to ensure its aerodynamic characteristics are given. When creating the An-148-100/An-158 family of aircraft, such level of the aircraft aerodynamic perfection was achieved, which ensured fulfillment of the specified requirements for their flight performance – maximum speed, cruising flight altitude and flight range with different payloads. The developed aerodynamic configuration made it possible to create a family of regional passenger high-wing planes with a flight speed of up to 870 km/h (true speed) (M = 0.8), which have no analogues in the world aviation industry. Developed for the An-148-100 / An- 158 aircraft, supercritical profiles of the new generation with a large maximum relative thickness formed the basis of the aerodynamic configuration of a high-speed wing with moderate sweep. The aircraft lift-to-drag ratio in cruise flight is Kcruise = 15.8, which corresponds to the worldwide values. Developed aerodynamic configuration of the wing high-lift devices provides high bearing properties of the wing during take-off and landing stages, which allows to fully meet the requirements for the runway required length of the base airfields Lrun = 1485...1950 m. Developed algorithms are implemented in the electric remote control system and provide necessary standard characteristics of stability, controllability and flight dynamics in the main control mode. Selected margins of the aircraft’s own static stability and effectiveness of its controls ensure safe completion of the flight in standby control mode. The certification flight tests of the An-148-100/An-158 airplanes confirmed full compliance of their take-off and landing performance, as well as the stability, controllability and flight dynamics characteristics with the requirements of the Certification basis in both standard and in failure situations tested in flight tests. Necessary and sufficient amount of experimental work was conducted in the lowspeed and high-speed wind tunnels of the ANTONOV SC and TsAGI to verify the aerodynamic and spin characteristics of the An-148-100/An-158 airplane models, which improved the aerodynamic configuration of the aircraft and its individual units and allowed to apply the work results in calculation of aircraft strength, as well as for development of their systems.

Design and Characterization of a High-Speed Subsonic Aeroacoustic Wind Tunnel

The high-speed aeroacoustic wind tunnel at Carleton University is a new facility commissioned with the purpose of facilitating experimental studies of turbulent boundary-layer (TBL)-induced surface pressure fluctuations. This research is primarily intended for applications related to aircraft cabin noise generation from structures exposed to high-speed flow. This open-jet blowdown wind tunnel is a unique facility in Canada and one of a few aeroacoustic wind tunnels in the world capable of achieving speeds up to Mach 0.8. Flow is delivered from a nozzle with dimensions of 6.1 by 15 cm to a test section enclosed within an anechoic chamber with internal dimensions of 1.9 by 0.88 by 1.95 m. This study details the complete design methodology for all major wind-tunnel components, including the numerical simulations performed in the validation of the designed components. The results of the test section background noise levels and TBL surface pressure fluctuation spectral behavior developed over a flat test section plate are compared with established data and empirical models available in the literature.

Aerothermoelastic experimental design for the AEDC/VKF Tunnel C: Challenges associated with measuring the response of flexible panels in high-temperature, high-speed wind tunnels

There is a lack of carefully-crafted aerothermoelastic experimental data that can be used for validation purposes. To address this need, the Air Force Research Laboratory Structural Sciences Center is currently planning an experiment in the Arnold Engineering Development Center von Kármán Facility Tunnel C to examine the aerothermoelastic response of flexible models that are representative of high-speed aircraft outer mold line panels. The test will utilize an infrared camera and the stereo digital image correlation technique to provide simultaneous, full-field measurements of the surface temperature and panel motion. This paper provides an overview of the proposed experiment and addresses challenges relevant to aerothermoelastic testing in high-temperature, high-speed wind tunnels.

Experimental investigation of end-wall VGJs in a compressor cascade

One of the important ways of improving compressor performance is to control three-dimensional (3D) separations which are related to the end-wall cross flow and corner separation. End-wall VGJs has been applied on the leading edge of the blade within a high subsonic compressor cascade to control the separation. Flow-control experiments are conducted in a high-speed wind tunnel with an instrumented NACA0065-k48. Detailed aerodynamic parameters are collected using a five-hole pressure probe and pressure tabs. Additionally, oil-flow visualization is used to obtain the topology of the flow field. Jet to inlet mass flow ratio is studied both in design and off design condition. The experimental results show that the VGJs cause a significant loss reduction both in design and off design condition. The control effect is more obvious with the increase of jet mass flow. The uniformity of the outlet flow and the static pressure rise are also improved. From the results of the oil flow experiment, the separation onset is delayed and the range of the reverse flow zone is also reduced, but the flow structure on the suction surface is almost unchanged.

Design and evaluation of a high-speed aeroacoustic wind tunnel

The high-speed aeroacoustic wind tunnel (HSAWT) at Carleton University is a new facility commissioned with the purpose of facilitating experimental studies of turbulent boundary layer (TBL) induced surface pressure fluctuations. This research is primarily intended for applications related to aircraft cabin noise generation from structures exposed to high-speed flow. This open-jet, blowdown wind tunnel is a unique facility in Canada and one of a few aeroacoustic wind tunnels in the world capable of achieving speeds up to Mach 0.8. Flow is delivered from a nozzle with dimensions of 6.1 cm × 15 cm to a test section enclosed within an anechoic chamber with internal dimensions of 1.9 m × 0.88 m × 1.95 m. This study details the complete design methodology for all major wind tunnel components, including the numerical simulations performed in the validation of the designed components. Results of preliminary test section flow characterization and chamber background noise measurements are discussed. Finally, experimental results of the TBL surface pressure fluctuation spectral behavior developed over a flat test section plate are compared with established data and empirical models available in literature.

Study of boundary layer transition on supercritical natural laminar flow wing at high Reynolds number through wind tunnel experiment

In order to achieve the goal of green aviation, energy conservation and emission reduction, laminar flow design technology has become a hot research topic. For transonic airliners, supercritical natural laminar flow wing design technology will significantly improve the aerodynamic performance (reduce flight drag, decrease fuel consumption and pollutant emissions). In this paper, airfoil optimization design system is applied to design the supercritical natural laminar flow airfoils based on high-precision boundary layer transition prediction technique. Then, three-dimensional layout of supercritical natural laminar flow wing is formed. Numerical simulations have been conducted to verify the laminar flow properties. In addition, the aerodynamic model with ratio of 1:10.4 is processed to measure boundary layer transition phenomena in the high speed and low turbulence wind tunnel in Netherlands. Temperature sensitive paint (TSP) technique is used to photograph laminar-turbulent distribution at different Mach numbers, Reynolds numbers and angels of attack. In the following content, boundary layer transition properties of the supercritical natural laminar flow wing are analyzed using TSP results and CFD simulations. Finally, key factors of supercritical natural laminar wing design and corresponding boundary layer transition properties are summarized. In addition, the research about transition properties of supercritical natural laminar flow wing at high Reynolds numbers have guiding significance for aircraft designers and transition researchers.

Performance and midspan wake measurements on a H-Darrieus in controlled conditions

Performance and wake measurements on a H-Darrieus vertical axis wind turbine are discussed on the basis of an extensive experimental campaign performed at the large scale, high speed wind tunnel of the Politecnico di Milano (IT). The paper proposes a combined mechanical and fluid-dynamic investigation by virtue of an advanced measurement system that allows to reconstruct both phase-resolved thrust and torque acting on the machine and the phase-resolved multi-dimensional velocity field in the wake. The aerodynamic torque is presented as a function of the azimuthal angle of revolution, while the velocity field in the wake is fully characterized by means of a point to point detailed measurement on the midspan plane, where the influence of both blade support struts and tip vortices is negligible.Particular care is taken in the description of the experimental setup as well as in the presentation of the measurements. The here proposed achievements can be considered as a benchmark for the validation of several classes of computational tools.

Influence of Airspeed and Adjuvants on Droplet Size Distribution in Aerial Applications of Glyphosate

Abstract. Drift is one of the most hazardous consequences of an improper aerial application of glyphosate. Wind, droplet size, application height, and distance to sensitive areas are the most important factors for drift. Droplet size is affected by nozzle, operating pressure, flight speed, deflection angle, and physicochemical properties of the spray solution. The objective of this study was to evaluate the effect of flight speed and the use of adjuvants on droplet size spectra in aerial applications of glyphosate. The study was conducted in a high-speed wind tunnel at the Pesticide Application Technology Laboratory (University of Nebraska-Lincoln, West Central Research and Extension Center, North Platte, Neb.). Aerial applications were simulated with four different airspeeds (44.4, 52.8, 61.1, and 69.4 m/s) and glyphosate combined with adjuvants (high surfactant oil concentrate, microemulsion drift reduction agent, nonionic and acidifier surfactant, polyvinyl polymer, and glyphosate alone). Droplet size spectra were evaluated using a Sympatec Helos laser diffraction instrument measuring 90 cm from the nozzle tip (CP11-4015). The volumetric droplet size distribution parameters (VMD, DV0.1, and DV0.9) and the percentage of droplets smaller than 100 µm were reported. The relative span was calculated to indicate the droplet size homogeneity [(DV0.9 - DV0.1) / DV0.5]. Glyphosate solutions with adjuvants had a larger VMD than the glyphosate alone solution at 44.4 m/s wind speed. At 69.4 m/s only the glyphosate solution with polymer had a larger VMD. Conversely, the glyphosate with polymer had the smallest DV0.1, and the greatest relative span and percentage of droplets smaller than 100 µm. Generally, adjuvants influence on droplet size was diminished or muted as the airspeed was increased. The polymer tested in this study failed as a drift agent reduction agent, especially at higher airspeeds. While not all polymers were tested, cautions should be taken if using these types of adjuvants in aerial applications. The interaction of airspeed and adjuvants influencing droplet size distribution in aerial applications of glyphosate should be considered by applicators in order to mitigate glyphosate drift to the surrounding environment. Further studies are necessary to better understand the interaction between solution viscosity and air shear effect on the atomization process and droplet size distribution, as well as confirm that trends hold true for other adjuvants in the polymer class. Although applicators tend to operate aircrafts with increased flight speeds in order to optimize the application time efficiency, this practice can reduce or mute adjuvants effects, decrease the droplet size distribution, and increase drift potential in aerial applications of glyphosate. Keywords: Drift reduction technologies, Flight speed, High-speed wind tunnel, Laser diffraction.

Droplet spectra and high-speed wind tunnel evaluation of air induction nozzles

A series of air induction nozzles were tested in a high-speed wind tunnel. Droplet size spectra were measured for four air induction nozzles (IDK-120-01, IDK-120-02, IDK-120-03 and IDK-120-04) each at three spray pressures (0.3, 0.4 and 0.5 MPa) and seven different air velocities (121.7, 153.4, 185.5, 218.4, 253.5, 277.5 and 305.5 km·h⁻¹). The measurement distance (0.15, 0.25 and 0.35 m) from the nozzle orifice was found to be important for the atomization of the droplets. The response surface method was used to analyze the experimental data. The results indicated that <i>D</i>v_0.1 and <i>D</i>v_0.5 of the droplets decreased quasi-linearly with increased wind speed, while <i>D</i>v_0.9 was affected by the quadratic of wind speed. <i>D</i>v_0.1, <i>D</i>v_0.5 and <i>D</i>v_0.9 of the droplets were all proportional to the orifice size, and were not markedly influenced by the spray pressure. The percentage of the spray volume consisting of droplets with a diameter below 100 <font style="font-family:Symbol">m</font>m (%<100 <font style="font-family:Symbol">m</font>m) was found to be quadratically related to wind speed, and was not markedly influenced by the spray pressure and orifice size. However, the effect of the orifice size on the %< 200 <font style="font-family:Symbol">m</font>m could not be ignored.

Experimental Investigation of the Boundary Layer Transition on a Laminar Airfoil Using Infrared Thermography

The transition in the boundary layer is investigated using infrared thermography (IRT). The study is carried out on a laminar airfoil in the transonic intermittent in-draft wind tunnel. The transition in the boundary layer is evocated using transition-generator strips of different thicknesses at two Mach numbers: 0.4 and 0.8. The tested transition-generators thickness to boundary layer displacement thickness ratio was from 0.42 to 1.25. The Reynolds number respect to the airfoil chord is: Re = 1.0 – 1.4·106. The six cases for different transition-generators thickness ratios were compared. The behaviours of laminar and turbulent boundary layers are discussed. The use of IRT has been proven to be an appropriate tool for detecting the transition of the boundary layer in high-speed wind tunnel testing.

An analysis on 45° sweep tail angle for blended wing body aircraft to the aerodynamics coefficients by wind tunnel experiment

This paper presents the analysis of a model from UiTM Blended Wing Body (BWB) UAV, Baseline V that has been tested at UPNM high speed wind tunnel. Baseline V has a unique design due to different NACA sections used for its fuselage, body, wing root, midwing, wingtip, tail root, tail tip and the tail is swept 45° backward. The purpose of this experiment is to study the aerodynamic characteristics when the tail sweeps 45° backward. The experiments are conducted several times using 71.5% scaled down model at about 49.58 m/s airspeed or 25 Hz. The tail angle deflection is fixed and set at zero angle. All the data obtained is analyzed and presented in terms of coefficient of lift, coefficient of drag and also lift-to-drag ratio, and is plotted against various angles of attack. The angles of attack used for this experiments are between −10° to +30°. The blockage correction such as solid blockage, wake blockage and streamline curvature blockage are calculated in order to obtain true performance of the aircraft. From the observation, Baseline V shows that the aircraft tends to stall at around +15°. The maximum L/D ratio achieved for Baseline V is 20.8, however it decreases slightly to 20.7 after blockage corrections.

Numerical analysis of high speed wind tunnel flow disturbance measurements using stagnation point probes

Since supersonic test facilities have tunnel noise that strongly influences boundary layer transition experiments, the determination of tunnel noise is of great significance to properly evaluate and interpret experimental results. The composition of tunnel noise, which consists of acoustic, entropy and vorticity modes, highly influences the boundary layer receptivity. The measurement of the separate modes is a major goal of ongoing research. In this study, the properties of stagnation point probes for a newly developed modal decomposition method for tunnel noise are investigated by direct numerical simulation. Pressure and heat flux responses of a stagnation point probe to various entropy and acoustic mode input functions are analysed to investigate how tunnel noise is perceived by corresponding sensor types. The interaction of the incident mode and the shock wave upstream of the probe is analysed and the resulting wave pattern in the subsonic region between shock wave and probe is evidenced. It is found that pure incident acoustic or entropy modes cause acoustic and entropy waves downstream of the shock wave whose strengths differ depending on the incident mode. The resulting wave pattern downstream of the shock wave is determined by postshock acoustic waves propagating bidirectionally between shock wave and probe. Formulating a model equation linking pressure and heat flux fluctuations to the initially caused postshock acoustic and entropy wave, a criterion for the applicability of stagnation point probes measuring pressure and heat flux fluctuations in the new modal decomposition method can be deduced: to distinguish between the incident mode types based on their pressure and heat flux signal the perception of initially generated entropy waves downstream of the shock wave by the heat flux sensor is crucial. The transfer function between entropy waves and heat flux is shown to have low pass filter characteristics and the cutoff Strouhal number could be estimated by control theory. The analysis of the frequency response to continuous incident waves corroborated this cutoff Strouhal number.

Study of Flow Characteristics in a Closed-Loop Low-Speed Wind Tunnel

Wind tunnel is an element or experimental device that plays an important role in the development of aerodynamics. In general, there are two types of wind tunnels: open-loop wind tunnels and closed-loop wind tunnels. Furthermore, based on the flow velocity in the wind tunnel, the wind tunnel can also be categorized into several types: low-speed wind tunnel and high-speed wind tunnel, including sub-sonic and supersonic wind tunnels. In this study it is used a low-speed closed-loop wind tunnel type. The maximum atainable velocity of airflow in the wind tunnel is about 46 m/s with turbulence intensity (TI) as low as 0.41 percent. The flow parameters that being evaluated in this study include the velocity profiles and intensity of turbulence (TI) in some parts or sections of the wind tunnel. Pressure measurements in the wind tunnel are performed using a Pitot tube connected to a calibrated pressure transducer. The measured values of pressures are then converted into the fluid velocities and turbulence intensities. The results show that the flow quality in the main test section of the wind tunnel is good enough. The intensity of the flow turbulence on the inlet side of the test section is about 0.41 percent at the centerline velocity of approximately 40 m/s. In some parts of the wind tunnel, turbulence intensity is still relatively high, as in the small elbow outlet where TI is higher than 18 percent.

Simulation of Time-Varying Spatially Uniform Pressure and Near-Surface Wind Flows on Building Components and Cladding

This paper describes a new full-scale testing apparatus for conducting performance evaluations of full-scale building envelope systems. The simulator can generate spatially uniform, time-varying pressure conditions associated with Saffir-Simpson Hurricane Wind Scale Category 5 winds while compensating for large air leakage through the specimen and also operate a high-speed wind tunnel, both with dynamic control. This paper presents system details, operating characteristics, and an early case study on the performance of large sectional door systems under wind pressure loading. Failure mechanisms are discussed, and finite element modeling is validated for two specimens. It demonstrates successful dynamic load control for large component and cladding systems, as well as simulation of flows near the building surface. These capabilities serve to complement other full-scale wind tunnel facilities by offering tools to generate ultimate load conditions on portions of the building. Further, the paper successfully demonstrates the utility of combining physical testing and computational analysis as a matter of routine, which underscores the potential of evolving full-scale testing to encompass cyber-physical approaches.

Experimental Investigation of Pressure Side Flow Separation on the T106C Airfoil at High Suction Side Incidence Flow

The objective of this work is to study the influence of a pressure side separation bubble on the profile losses and the development of the bubble in the blade passage. For the experimental investigations, the T106 profile is used, with an increased loading due to an enlarged pitch to chord ratio from 0.799 to 0.95 (T106C). The experiments were performed at the high-speed cascade wind tunnel of the Institute of Jet Propulsion at the University of the Federal Armed Forces Munich. The main feature of the wind tunnel is to vary Reynolds and Mach number independently to achieve realistic turbomachinery conditions. The focus of this work is to determine the influence of a pressure side separation on the profile losses and hence the robustness to suction side incidence flow. The cascade is tested at four incidence angles from 0 deg to −22.7 deg to create separation bubbles of different sizes. The influence of the Reynolds number is investigated for a wide range at constant exit Mach number. Therefore, a typical exit Mach number for low pressure turbines in the range of 0.5–0.8 is chosen in order to consider compressible effects. Furthermore, two inlet turbulence levels of about 3% and 7.5% have been considered. The characteristics of the separation bubble are identified by using the profile pressure distributions, whereas wake traverses with a five hole probe are used to determine the influence of the pressure side separation on the profile losses. Further, time-resolved pressure measurements near the trailing edge as well as single hot wire measurements in the blade passage are conducted to investigate the unsteady behavior of the pressure side separation process itself and also its influence on the midspan passage flow.

BLADE ANGLE EFFECT ON DROPLET SIZE SPECTRUM OF ROTARY ATOMIZERS USED IN BRAZIL

The effect of blade angle on droplet size spectrum of five rotary cage atomizers and one rotary disc atomizer used in Brazil was evaluated in a high speed wind tunnel, with an air speed of 180 km h−1. This study included the characterization of the droplet size spectrum, via laser diffraction instrument, generated by three blades angles, of 45, 60 and 75 degrees. The spray solution was composed of Picoxystrobin+ Cyproconazole fungicide (SC), at 20 mL c.p. L−1, and at a flow rate of 6 L min−1. As the angle decreased from 75 to 45 degrees, the rotational speed of the atomizers increased and the volume median diameter (VMD) decreased. However, increasing the rotational speed also increased the percentage of droplets smaller than 100 µm (% < 100 µm). At the blade angles of 45 and 60 degrees the atomizers showed that % < 100 µm was higher than 20% and VMD was smaller than 198 µm. The disc type atomizer resulted in the lower values of relative span (RS). The use of 75 degrees blade angle produced the highest values of VMD and the lowest values of % < 100 µm; these parameters were also affected by atomizer model and brand.

Experimental investigation of flow-induced vibration of a pitch–plunge NACA 0015 airfoil under deep dynamic stall

The flow-induced vibration of a NACA 0015 airfoil model with pitch and plunge degrees of freedom is investigated in a high-speed wind tunnel using motion sensors, pressure sensors on the airfoil surface and synchronized high-speed Schlieren visualizations of the unsteady flow field at Reynolds numbers Re=180000–570000. Compared to other studies, the model has considerably smaller dimensions (with a chord length of 59.5mm) and operates at higher flow velocities (from 37 to 125m/s). With a relatively low pitch to plunge natural frequency ratio and zero initial incidence angle, the model is highly susceptible to deep dynamic stall instability with the peak-to-peak pitch amplitude reaching up to 90°. The limit cycle response of the system as a function of freestream flow velocity is reported in detail, together with synchronized Schlieren visualizations of the flow field revealing the boundary layer behavior during dynamic stall. With increasing inflow velocity, the plunge amplitude increases dramatically, accompanied also by slight rise in the frequency of oscillation and decrease of the phase lag between pitch and plunge. The pitch amplitude has a maximum at 62m/s and further decreases with increasing flow velocities.