Wind Tunnel Investigation Research Articles

Wind tunnel investigation of hemispherical forebody interaction on the drag coefficient of a D-shaped model

PurposeAn experimental investigation of hemispherical forebody interaction effects on the drag coefficient of a D-shaped model is carried out for three-dimensional flow in the subcritical range of Reynolds number 1 × 105 ≤ Re ≤ 1.8 × 105. To study the interaction effect, hemispherical shapes of various sizes are attached to the upriver of the D-shaped bluff body model. The diameter of the hemisphere (b1) varied from 0.25 to 0.75 times the diameter of the D-shaped model (b2) and its gap from the D-shaped model (g/b2) ranged from 0.25 to 1.75 b2.Design/methodology/approachThe experiments were carried out in a low-speed open-circuit closed jet wind tunnel with test section dimensions of 1.2 × 0.9 × 1.8 m (W × H × L) capable of generating maximum velocity up to 45 m/s. The wind tunnel is equipped with a driving unit which has a 175-hp motor with three propellers controlled by a 160-kW inverter drive. Drag force is measured with an internal six-component balance with the help of the Spider 3013 E-pro data acquisition system.FindingsThe wind tunnel results show that the hemispherical forebody has a diameter ratio of 0.75 with a gap ratio of 0.25, resulting in a maximum drag reduction of 67%.Research limitations/implicationsThe turbulence intensity of the wind tunnel is about 5.6% at a velocity of 18 m/s. The uncertainty in the velocity and the drag coefficient measurement are about ±1.5 and ±2.83 %, respectively. The maximum error in the geometric model is about ±1.33 %.ractical implicationsThe results from the research work are helpful in choosing the optimum spacing of road vehicles, especially truck–trailer and launch vehicle applications.Social implicationsDrag reduction of road vehicle resulting less fuel consumption as well as less pollution to the environment. For instance, tractor trailer experiencing approximately 45% of aerodynamics drag is due to front part of the vehicle. The other contributors are 30% due to trailer base and 25% is due to under body flow. Nearly 65% of energy was spent to overcome the aerodynamic drag, when the vehicle is traveling at the average of 70 kmph (Seifert 2008 and Doyle 2008).Originality/valueThe benefits of placing the forebody in front of the main body will have a strong influence on reducing fuel consumption.

Wind-Tunnel-in-the-Loop Exploration and Optimization of Active Flow Control Parameters

This paper considers the use of surrogate-based analysis and optimization (SBAO) methods to investigate the performance of pulsed jet actuators for active separation control in a wind tunnel. Two experimental setups are examined: pressure-induced separation on a one-sided diffuser and trailing-edge separation on a NACA 64A-015 airfoil. In both cases the modeling is done using Gaussian process regression (kriging), and the investigated active-flow-control parameters are the amplitude, frequency, and duty cycle of the actuators that are used to mitigate boundary-layer separation. In the diffuser test case, a parameter-space exploration is conducted to examine the effect of the three input parameters on the amount of reverse flow detected by an array of calorimetric shear-stress sensors. In the airfoil test case, an optimization strategy is followed to maximize an objective function constructed with the airfoil sectional lift coefficient and the mass flow consumption of the actuators. Both experiments consistently indicate that lowering the duty cycle of the pulsed-jet actuators below 0.5 may lead to efficiency gains in active separation control by limiting their mass flow consumption for equal performance, but with a concomitant supply pressure increase. Overall, the results presented herein demonstrate that SBAO methods could provide a potential for more efficient wind tunnel investigations involving multiparameter problems.

Wind Tunnel Investigation of the Icing of a Drone Rotor in Forward Flight

The Bell Textron APT70 is a UAV concept developed for last mile delivery and other usual applications. It performs vertical takeoff and transition into aircraft mode for forward flight. It includes four rotor each with four rotating blades. A test campaign has been performed to study the effects of ice accretion on rotor performance through a parametric study of different parameters, namely MVD, LWC, rotor speed, and pitch angle. This paper presents the last experimentations of this campaign for the drone rotor operating in forward flight under simulated icing conditions in a refrigerated, closed-loop wind tunnel. Results demonstrated that the different parameters studied greatly impacted the collection efficiency of the blades and thus, the resulting ice accretion. Smaller droplets were more easily influenced by the streamlines around the rotating blades, resulting in less droplets impacting the surface and thus slower ice accumulations. Higher rotation speeds and pitch angles generated more energetic streamlines, which again transported more droplets around the airfoils instead of them impacting on the surface, which also led to slower accumulation. Slower ice accumulation resulted in slower thrust losses, since the loss in performances can be directly linked to the amount of ice accreted. This research has not only allowed the obtainment of very insightful results on the effect of each test parameter on the ice accumulation, but it has also conducted the development of a unique test bench for UAV propellers. The new circular test sections along with the new instrumentation installed in and around the tunnel will allow the laboratory to be able to generate icing on various type of UAV in forward flight under representative atmospheric conditions.

The lidar probe volume averaging effect: A wind tunnel investigation in streamwise turbulence with continuous-wave lidar

The main limitation of lidars to capture the turbulence is the filtering of small-scale fluctuations within the probe volume, which is far less significant with conventional anemometers. In this study, the probe volume averaging effect on the streamwise turbulence statistics is investigated in the wind tunnel. Different turbulent flows, which exhibit distinct turbulence intensities and integral length scales are generated and subsequently captured using a short-range continuous-wave WindScanner with different probe volumes. Hot wire measurements are performed as a reference. The results indicate that the turbulence intensity (TI) is underestimated using conventional lidar methods compared to the hot wire measurements. The relative error increases with the increasing ratio of probe volume over integral length scale (l p /L) which is the indication of probe volume averaging. The TI is underestimated by 4 % at l p /L = 0.5 and by 63 % at the largest tested l p /L = 11.3 with the conventional lidar method. However, the TI estimated from the averaged Doppler spectrum of the lidar compensates for the probe volume averaging effect and shows a better agreement with the hot wire measurements with an average overestimation of 7.8 %. This study shows that the continuous-wave lidars have the potential to estimate the TI under different flow conditions using the averaged Doppler spectrum method.

Wind tunnel investigation on the recovery and dynamics of the wake of a floating offshore wind turbine subjected to low inflow turbulence

Floating offshore wind turbines (FOWT) operate in various turbulent conditions, including low turbulence intensity situations (TI∞ ≤ 5%). In this paper, we investigate experimentally the wake of a model floating wind turbine subjected to inflow turbulence up to TI∞ ≈ 3%. We consider idealised surge platform motion and analyse wake measurements at different downstream positions x ∈ [4D, 8D]. The results show that rotor movements enhance wake recovery compared to the fixed wind turbine, especially for TI∞ ≤ 2%. The recovery of the moving wind turbine wake is progressively less affected by motion with increasing TI∞ . Both amplitude and frequency of motion are key parameters that drive wake recovery and dynamics. We found in the wake large coherent structures induced by the platform movements, which allow a faster transition to the far wake but may cause increased loading on downstream turbines.

On the impact of different static induction control strategies on a wind turbine wake

This study provides a wind tunnel investigation to identify effective ways of derating an upstream turbine for mitigating wake-induced power losses. Short-range continuous-wave lidar measurements are used to remotely map the time-averaged wake characteristics of a controllable model wind turbine under uniform inflow with negligible turbulence. The analysis focuses on comparing four distinct static induction control (SIC) strategies, each at targeted derating levels of 5 % and 10 %, against a conventional greedy strategy. The results indicate that pitch-to-feather combined with an increased tip-speed ratio is the most favourable approach for minimising wake losses in a two-turbine setup. Notably, power gains of up to 3.8 % are achieved for partial and full wake overlap conditions at 5 % derating and small turbine spacing. These observations are consistent with previous field experiments, suggesting that SIC may be advantageous in wind farms with closely spaced turbines. Overall, these findings underscore the importance of carefully selecting and understanding the implemented derating strategy for supporting wind farm flow control applications.

Wind tunnel investigations of an individual pitch control strategy for wind farm power optimization

Abstract. This article presents the results of an experimental wind tunnel study which investigates a new control strategy named Helix. The Helix control employs individual pitch control for sinusoidally varying yaw and tilt moments to induce an additional rotational component in the wake, aiming to enhance wake mixing. The experiments are conducted in a closed-loop wind tunnel under low-turbulence conditions to emphasize wake effects. Highly sensorized model wind turbines with control capabilities similar to full-scale machines are employed in a two-turbine setup to assess wake recovery potential and explore loads on both upstream and downstream turbines. In a single-turbine study, detailed wake measurements are carried out using a fast-response five-hole pressure probe. The results demonstrate a significant improvement in energy content within the wake, with distinct peaks for clockwise and counterclockwise movements at Strouhal numbers of approximately 0.47. Both upstream and downstream turbine dynamic equivalent loads increase when applying the Helix control. The time-averaged wake flow streamwise velocity and rms value reveal a faster wake recovery for actuated cases in comparison to the baseline. Phase-locked results with azimuthal position display a leapfrogging behavior in the baseline case in contrast to the actuated cases, where distorted shedding structures in the longitudinal direction are observed due to a changed thrust coefficient and an accompanying lateral vortex shedding location. Additionally, phase-locked results with the additional frequency reveal a tip vortex meandering, which enhances faster wake recovery. Comparing the Helix cases with clockwise and counterclockwise rotations, the latter exhibits slightly higher gains and faster wake recovery. This difference is attributed to Helix' additional rotational component acting in either the same or the opposite direction as the wake rotation. Overall, both Helix cases exhibit significantly faster wake recovery compared to the baseline, indicating the potential of this technique for improved wind farm control.

Wind Tunnel Investigation of Transient Propeller Loads for Non-Axial Inflow Conditions

Recent developments in electrical Vertical Take-off and Landing (eVTOL) vehicles show the need for a better understanding of transient aero-mechanical propeller loads for non-axial inflow conditions. The variety of vehicle configurations conceptualized with different propellers in terms of blade geometry, number of blades, and their general integration concept results in aerodynamic loads on the propellers which are different from those on conventional fixed-wing aircraft propellers or helicopter rotors. Such varying aerodynamic loads have to be considered in the vehicle design as a whole and also in the detailed design of their respective electric propulsion systems. Therefore, an experimental approach is conducted on two different propeller blade geometries and a varying number of blades with the objective to explore the characteristics at non-axial inflow conditions. Experimental data are compared with calculated results of a low-fidelity Blade Element Momentum Theory (BEMT) approach. Average thrust and side force coefficients are shown to increase with inflow angle, and this trend is captured by the implemented numerical method. Measured thrust and in-plane forces are shown to oscillate at the blade passing frequency and its harmonics, with higher amplitudes at higher angles of inflow or lower number of blades.

Wind effects on rectangular plan building located in a hilly terrain: A wind tunnel investigation

Wind effects on rectangular plan building located in a hilly terrain: A wind tunnel investigation

Effect of facet gap on heliostat wind loading

Multi-facet heliostats are more versatile and advantageous in design compared to single facet heliostats, while generating new design challenges. Multi-facet designs can reduce manufacturing costs, allow for decentralisation of power supply, and bring the option of face down stow. Addition of a gap between two facets, changes the flow structure around the heliostat. The effect of gap between two heliostat facets is therefore investigated on wind loads through experimental investigation in a large wind tunnel. A heliostat model was placed in a simulated atmospheric boundary layer at The University of Adelaide wind tunnel. The investigation covered gap ratios between two panels (gap spacing/facet width) from 0 to 2, and panel aspect ratios (facet width/chord length) of 0.35 to 0.65, forming a complete heliostat aspect ratio of 0.7 to 1.3 with no gap. Wind load coefficients were determined using load cell measurements at the base, and application of differential pressure sensors on the surface, of the heliostat model. Findings indicate the presence of a gap, in general, increases the wind load on the heliostat, with facet aspect ratio exacerbating the results. The maximum load cases shift further into the operating range of heliostats where a change in centre of pressure, due to a change in gap ratio, shifts maximum coefficients from an elevation angle of 30° to 45° for lift force and hinge moment, and 90° to 75° for azimuthal moment. Increasing loads on elevation and azimuth drives potentially increases tracking deviations and beam misalignment, reducing concentrated solar power plant performance.

Formulation of justifiable wind loading distributions up tall buildings derived from HFFB measurements

For the general case of non-linear and combined sway and twist mode shapes, analysis of HFFB measurements gives rise to serious challenges and various techniques have been developed using significant assumptions. This is because it is not possible to directly obtain the distribution of varying fluctuating wind loads throughout the height of tall buildings. This paper proposes a straightforward HFFB-based wind load/twist distribution approach in the time domain to predict the wind-induced dynamic response of tall buildings. Using this framework, it is possible to overcome the deficiencies of mode shape correction factor approach, and the complexity and impracticality of alternative approaches for tall buildings. Two 1:300 scale rigid models of benchmark tall buildings, IAWE Buildings A and B, have been selected to perform a detailed wind tunnel investigation as subjects to evaluate this proposed HFFB approach study. Building A has complex 3D mode shapes combining sway and twist, whereas the simpler Building B has uncoupled linear mode shapes in sway and twist. The high frequency pressure integration (HFPI) wind tunnel technique was utilised to measure surface pressure information in separate tests to obtain the reference wind loading for validation of the HFFB predictions. Furthermore, a commonly used HFFB mode shape correction factor approach was used to estimate the dynamic wind responses which were compared to those from the proposed approach. From the comparison between the aerodynamic and dynamic wind results from proposed HFFB approach and reference HFPI results, it is found that the proposed HFFB approach can predict the vertical distributions of the wind forces and torque (wind loads) with acceptable accuracy for carrying out the conceptual stage of tall building design.

A wind tunnel investigation of the effects of end and laminar/turbulent inflow conditions on cylinder vortex-induced vibrations

The influence of end and inflow conditions on the vortex-induced vibrations of a cylinder is studied on the basis of wind tunnel experiments, combining measurements of the body displacement and flow velocity in its wake. The cylinder of length-to-diameter aspect ratio 5.5 has one end exposed to the current. It is elastically mounted in the cross-flow direction, with low damping. The structure to displaced fluid mass ratio is close to 1000. The behavior of the system is explored over a range of values of the reduced velocity, U⋆, defined as the inverse of the oscillator natural frequency, non-dimensionalized by the inflow velocity (U∞) and the cylinder diameter (D), typically between 4 and 8, at a Reynolds number of the order of 104, based on U∞ and D. Three end conditions are examined: two free-end conditions with either a flat or a hemispherical shape, and a condition where a fixed plate is placed close to the flat end. Three inflow states are considered: a laminar condition and two grid-generated turbulent conditions of different turbulence intensity levels (up to 10%) and comparable integral length scales, around 30% of D. Vibrations characterized by bell-shaped evolutions of their magnitude with U⋆ develop, under flow-body synchronization (lock-in), in all conditions, with peak amplitudes ranging from 4% to 12% of D. The free end causes a shift of the response bell-shaped curve towards higher U⋆ values. The shift may be such that there is no overlap between the vibration domains in the end-plate and free-end conditions. The passage from laminar to turbulent inflow conditions is found to attenuate this shift. A clear reduction of vibration amplitude is observed when the end plate is removed, and the amplitude is further reduced when the flat end is replaced by the hemispherical one. On the other hand, turbulent inflows induce a global enhancement of the vibration amplitudes, which may reach +45% relative to the laminar stream condition. The end/inflow conditions are also shown to impact the regularity of the structural responses.

Wind tunnel investigation of blade pitch effect for performance improvement of an asymmetric bladed H-Darrieus VAWT under low wind speed condition

In this paper experimental investigation is conducted to analyse the blade pitch effect on the performance improvement (self-starting and dynamic performance) of a NACA 63415 asymmetric bladed H-Darrieus VAWT at low wind speed conditions (5.0 and 6.0 m/s). It has been found that the performance of the considered VAWT has improved with a change of blade pitch angle (β) from negative to positive value. A maximum power coefficient (Cp) of 0.086 is obtained at a tip speed ratio (TSR) of 1.73 at a wind speed of 6.0 m/s for β = + 5°. Further turbulence intensity (TI) and flow non-uniformity (NU) are also calculated. In this case, TI of 2.6% and 2.4% is calculated from experimentation along with 4% and 3.33% non-uniformity (NU) for wind speeds 5.0 and 6.0 m/s, respectively, which are responsible for Cp improvement.

CFD wind tunnel investigation for wind loads of steel television tower with grid structure

Television(TV) towers with grid structures serve as broadcasting frequency modulation or television transmission signals and provide sightseeing opportunities. Accurate wind load information is critical to the design of these towers to ensure their resistance to wind. Due to the scaling ratio of the test model, wind tunnel test can only determine the overall wind load, resulting in the loss of wind load information on specific rods. However, there is currently a lack of research on the wind loads of the specific rods of a core tube with a grid structure. This article focuses on this special topic. Computational fluid dynamics (CFD) technology, which was validated based on the Commonwealth Advisory Aeronautical Research Council (CAARC) model, was employed in simulation for a towering television tower with a grid structure. Wind load distributions of the grid structure and core tube were studied, including flow streamlines, velocity profiles and wind pressure distributions. The results indicate that the wind pressure distribution on the outer surface of the cross rods is similar at different heights. Net wind pressures of the rods in the flow separation zone are close to 0, which significantly reduces the across-wind load. Different wind direction angles significantly influence the wind load of the grid structure but slightly influence the core tube. The simulation results can provide a reference for wind load design of similar grid structures.

Full-scale monitored wind and response characteristics of a suspension bridge compared with wind tunnel investigations at the design stage

Structural health monitoring of long-span bridges makes it possible to assess the assumptions and considerations in the design stage of the structures through measurements of their structural response and environmental conditions. In wind-resistant design of long-span bridges, the wind-induced dynamic buffeting response is difficult to assess as the uncertainty in the loading and the structural and aerodynamic characteristics is high. In that case, one of the best sources of information is wind tunnel tests, in addition to field measurements and analytical considerations. However, it is unclear if such methods can provide reliable information for the designer since, typically, many uncertainties and assumptions are involved in such a process. Here, we evaluate the scaled full aeroelastic and terrain model tests carried out during the design stage of the Gjemnessund Bridge in Norway through comparisons with full-scale monitoring data spanning five years. The monitoring system and the data are presented along with the wind tunnel study. The results from both campaigns are analyzed and critically discussed, emphasizing implications for the wind-resistant design of long-span bridges.

Wind-Tunnel Investigation of the ILCA 7 MKII Sail in Downwind Conditions

Aerodynamic coefficients from wind-tunnel tests are presented for the ILCA 7 in all six degrees of freedom. Two apparent wind speeds are considered: a light wind case corresponding to 4 m s-1 at full scale and a strong wind case corresponding to 7 m s-1. The light wind tests comprise five apparent wind angles, seven sheet angles, three kicker trims and three heel angles. For the strong wind case the dinghy is assumed sailing upright and only dead downwind, but with four sheet angles and three kicker trims. The scale is 1/7, which gives a reasonable blockage in the wind-tunnel. Blockage corrections are obtained using CFD. Correct scaling of the sail stretch, and mast bend is achieved with the full-scale sail cloth and a solid stainless-steel mast exposed to a wind speed √7 times larger than at full-scale. However, the Reynolds number is √7 times smaller. The main result of the investigation is the comprehensive data set, which is available on a public server. This data can be used in a VPP to optimise downwind sailing in smooth water. Several interesting conclusions can also be drawn directly from the data. Thus, for the light wind case the best sheet angle is 90° regardless of the course sailed. However, for the strong wind case (dead downwind), the best angle is 80°. In all cases the tight kicker trim produces the largest drive force and in the light wind case also the smallest side force.

A new method for obtaining wind loads by robustly combining part-model test results

The authors propose a new method to synthesise the time series of wind loads up the height of a building by robustly combining part-model test results and show that they are essentially identical to those sampled simultaneously from a complete model. A pressure-tapped circular cylinder was built to study and validate this segmented model test method using high frequency pressure integration. The detailed mathematical derivation of the synthetic wind load (SWL) method is presented. The dynamic response of a hypothetical chimney using uncorrected wind loads from two independent wind tunnel tests of the circular cylinder model is found to be underestimated considerably compared to using wind loads from simultaneously sampled pressure taps. However, the dynamic response of the chimney using the SWL method to robustly combine the wind loads from two independent wind tunnel tests is almost identical to the dynamic response of the chimney using pressure tap data sampled simultaneously over the whole model. The establishment of this method is of great importance for the wind tunnel investigation of very high aspect ratio buildings where a model of the entire building cannot be tested within typical wind tunnel test sections because the Reynolds number would be too low, or the model section would be too narrow to contain the pressure tubes, and part-models need to be tested.

Wind Tunnel Investigation of Typical Strategic Missile Configuration at High Angle of Attack

The present wind tunnel investigation is a part of a project studying the effectiveness of flat fin control on short-range strategic missile at high angle of attack. As a part of this program, the longitudinal aerodynamic coefficients were computed analytically and were compared with estimates obtained through wind tunnel testing. Wind tunnel tests were conducted over a range of angle of attack from -15° to +45° at a free stream speed of 60m/s. Aerodynamic coefficients were generated for various missile configurations. These coefficients were then compared with the estimates obtained analytically. It was conjectured that, at high angle of attack, vortices shaded by the body interact with the local flow near the fins and drastically alters the stability characteristics of the missile. The subject missile has a small hemispherical nose as compared to most of the missiles having conical or ogival nose. For such a configuration sufficient theoretical/experimental data are not available. Thus, it was important to generate longitudinal aerodynamic data for the range of angle of attack upto which the theoretical model can be used to evaluate the aerodynamic stiffness of the missile. Such a model structure is required for postulating aerodynamic model in estimation algorithm, used for parameter estimation from flight data of the subject missile.

Experimental Study of an Asymmetric Tandem Wing Configuration for Drone Application

A low-speed wind tunnel investigation characterizing the performance of an asymmetric tandem wing is presented. Wind tunnel data were supported by numerical modeling and flow visualization. The opposing wing halves of a rectangular AR=6.23 wing were systematically shifted fore and aft along a central fuselage to yield asymmetry. The results show that the lift curve slope, minimum drag coefficient, and Oswald efficiency factor are weakly affected by asymmetry, a result supported by numerical computations. The maximum lift-to-drag ratio, however, dropped essentially linearly with increasing asymmetry, a consequence of the reduced aspect ratio of each wing half decreasing the lift coefficient for minimum drag. Comparison of the experimental results with a symmetric wing with conventional empennage suggests that an asymmetric tandem wing configuration may be a viable geometry for deployable flight vehicles such as tube-launched drones.

Aeroelastic wind tunnel investigations on rectangular-planed air-supported membrane structures

This study implements aeroelastic wind tunnel experiments on rectangular-planed air-supported membrane structures. With the goal of identifying possible wind response patterns, experiments are conducted with a wide range of wind velocities, internal pressures, and membrane tensile stiffness, including cases close to similarity requirements for simulating prototypes. Wind pressure measurements on the rigid model are performed to serve as a reference, and during subsequent aeroelastic wind tunnel tests, time-averaged and fluctuating wind responses of air-supported membrane structures are observed to significantly increase with lower internal pressures, higher wind speeds, more incoming turbulence, and less membrane tensile stiffness. Two distinct patterns of wind response, buffeting, and aeroelastic instability, are observed within the aeroelastic wind tunnel experiments. These two patterns exhibit significant differences in terms of fluid–structure interaction mechanisms and statistics of structural wind responses. This research emphasizes the influences of membrane elasticity and incoming turbulence on variations of structural wind response patterns. Aeroelastic instability is observed on models with extreme flexibility and relatively lower incoming turbulence, while the buffeting pattern is observed with other configurations, including cases that approach the similarity requirements for simulating air-supported membrane structures in practice.