Wind Tunnel Investigation Research Articles

Wind loading on catenary vault structures

Catenary vault structures are increasingly being utilised as an efficient alternative to the traditional circular vault. However, little is known regarding wind loading effects, in particular the pressure distribution, over these forms. Consequently, applicability of the data given for circular vaults used for the design of catenary vaults is also uncertain. In this paper the results of a wind-tunnel investigation and their implications on the design of catenary vaults are discussed. A series of tests were undertaken to assess the effects of variation in vault geometry and wind orientation on surface pressures measured over these structures. These parameters are evaluated to clarify their influence on the loading on catenary vaults. Only the results relating to mean and root-mean-square pressure coefficients are reported, in line with wind loading standardisation practice (if localised pressures are relevant, the designer is referred to expert advice or an adoption of the data from similar geometrical forms). The primary focus of the investigation is to examine the applicability of the design data given in SANS 10160-3:2011 (SANS 2011b) (referring to circular and duo-pitched roofs) to catenary structures. Subsequently, the merit of developing a set of exclusive design coefficients relating to catenary vaults is considered.

Effect of Leading-Edge Slats at Low Reynolds Numbers

One of the most commonly implemented devices for stall control on wings and airfoils is a leading-edge slat. While functioning of slats at high Reynolds number is well documented, this is not the case at the low Reynolds numbers common for small unmanned aerial vehicles. Consequently, a low-speed wind tunnel investigation was undertaken to elucidate the performance of a slat at Re = 250,000. Force balance measurements accompanied by surface flow visualization images are presented. The slat extension and rotation was varied and documented. The results indicate that for small slat extensions, slat rotation is deleterious to performance, but is required for larger slat extensions for effective lift augmentation. Deployment of the slat was accompanied by a significant drag penalty due to premature localized flow separation.

Wind tunnel testing of scaled models of a newly developed Darrieus-style vertical axis wind turbine with auxiliary straight blades

Renewable sources of energy, needed because of the increasing price of fossil derivatives, global warming and energy market instabilities, have led to an increasing interest in wind energy. Among the different typologies, small scale Vertical Axis Wind Turbines (VAWT) present the greatest potential for off grid power generation at low wind speeds. In the present work, wind tunnel investigations about the performance of an innovative configuration of straight-blades Darrieus-style vertical axis micro wind turbine, specifically developed for small scale energy conversion at low wind speeds, has been made on scaled models. The micro turbine under investigation consists of three pairs of airfoils. Each pair consists of a main and auxiliary airfoil with different chord lengths. A standard Darrieus configuration, consisting of three single airfoils, was also tested for comparison. The experiments were conducted in a closed circuit open chamber wind tunnel facility available at the Laboratory of Industrial Measurements (LaMI) of the University of Cassino and Lazio Meridionale (UNICLAM). Measured data were reported in terms of dimensionless power and torque coefficients for dynamic performance analysis and static torque coefficient for static performance analysis. The adoption of auxiliary airfoils has demonstrated to give more dynamic torque at the lower wind speeds with respect to a standard Darrieus rotor, resulting in better performance for all the wind speeds considered. In terms of dynamic power coefficient, the standard Darrieus configuration presented slightly better performance for the highest wind speed analyzed. The proposed configuration showed also an higher value of static torque coefficient with respect to the standard Darrieus micro turbine, resulting in a better self-starting ability.

Measuring structure deformations of a composite glider by optical means with on-ground and in-flight testing

In aeronautical research experimental data sets of high quality are essential to verify and improve simulation algorithms. For this reason the experimental techniques need to be constantly refined. The shape, movement or deformation of structural aircraft elements can be measured implicitly in multiple ways; however, only optical, correlation-based techniques are able to deliver direct high-order and spatial results. In this paper two different optical metrologies are used for on-ground preparation and the actual execution of in-flight wing deformation measurements on a PW-6U glider. Firstly, the commercial PONTOS system is used for static tests on the ground and for wind tunnel investigations to successfully certify an experimental sensor pod mounted on top of the test bed fuselage. Secondly, a modification of the glider is necessary to implement the optical method named image pattern correlation technique (IPCT), which has been developed by the German Aerospace Center DLR. This scientific technology uses a stereoscopic camera set-up placed inside the experimental pod and a stochastic dot matrix applied to the area of interest on the glider wing to measure the deformation of the upper wing surface in-flight. The flight test installation, including the preparation, is described and results are presented briefly. Focussing on the compensation for typical error sources, the paper concludes with a recommended procedure to enhance the data processing for better results. Within the presented project IPCT has been developed and optimized for a new type of test bed. Adapted to the special requirements of the glider, the IPCT measurements were able to deliver a valuable wing deformation data base which now can be used to improve corresponding numerical models and simulations.

A wind tunnel investigation of particle segregation, ripple formation and armouring within sand beds of systematically varied texture

AbstractThis paper reports on a wind tunnel investigation of particle segregation, ripple formation and surface armouring within sand beds of systematically varied particle size distribution, from coarsely skewed to bimodal. By design, the system was closed with no external inputs of mass from an external particle feed. Particles too coarse to travel in saltation for the given range in wind speed were dyed red in order to distinguish them in optical images from finer sand particles, which could be entrained into the unidirectional airflow. A 3D laser scanner measured the changing bed topography at regular time intervals during 18 experiments involving varied combinations of wind speed and bed texture. Image classification techniques were used to investigate the coincident self‐organization of the two populations of particles, as distinguished by their colour. As soon as saltation commenced, some of the red particles segregated into thin discontinuous patches. Particle trapping and sheltering on these rough patches was strongly favoured, causing them to grow preferentially. During the earliest stages of formation, bedform growth coincided with: (i) rapid coarsening of the surface texture; and (ii) the merging of proto‐ripple ‘crests’ to generate larger rhythmic bedforms of lower frequency. Consistent with previous work, ripple size was observed to increase under stronger winds when not exceeding the threshold for entrainment of the coarse‐mode or red particles from the crest. With declining rates of mass transport and particle segregation as the bed surface armoured, and the consequent deceleration of ripple propagation through to the end of each experiment, all surfaces eventually attained a steady‐state morphometry. At saturation, the largest ripples developed on beds having the lowest initial concentration of red particles. Copyright © 2016 John Wiley & Sons, Ltd.

Fully Automated Operational Modal Analysis using multi-stage clustering

The interest for robust automatic modal parameter extraction techniques has increased significantly over the last years, together with the rising demand for continuous health monitoring of critical infrastructure like bridges, buildings and wind turbine blades. In this study a novel, multi-stage clustering approach for Automated Operational Modal Analysis (AOMA) is introduced. In contrast to existing approaches, the procedure works without any user-provided thresholds, is applicable within large system order ranges, can be used with very small sensor numbers and does not place any limitations on the damping ratio or the complexity of the system under investigation. The approach works with any parametric system identification algorithm that uses the system order n as sole parameter. Here a data-driven Stochastic Subspace Identification (SSI) method is used. Measurements from a wind tunnel investigation with a composite cantilever equipped with Fiber Bragg Grating Sensors (FBGSs) and piezoelectric sensors are used to assess the performance of the algorithm with a highly damped structure and low signal to noise ratio conditions. The proposed method was able to identify all physical system modes in the investigated frequency range from over 1000 individual datasets using FBGSs under challenging signal to noise ratio conditions and under better signal conditions but from only two sensors.

Wind tunnel investigation of horizontal and vertical sand fluxes of ascending and descending sand particles in aeolian sand transport

AbstractThe horizontal and vertical sand mass fluxes in aeolian sand transport are investigated in a wind tunnel by PTV (particle tracking velocimetry). According to the particle velocity and volume fraction of each individual particle from PTV images, the total horizontal sand mass flux, the horizontal mass fluxes of ascending and descending sand particles, and upward and downward vertical sand fluxes are analyzed. The results show that the horizontal mass fluxes of ascending and descending sand particles generally decrease with the increase of height and can be described by an exponential function above about 0.03 m height. At the same friction velocity, the decay heights of the total horizontal sand mass flux and the horizontal mass fluxes of ascending and descending sand particles are very similar. The proportion of horizontal mass flux of ascending sand particles is generally about 0.3–0.42, this means the horizontal mass flux of descending sand particles makes an important contribution to the total horizontal sand mass flux. Both the upward and downward vertical sand mass fluxes generally decrease with height and they are approximately equal at the same height and friction velocity. The relation between upward (or downward) vertical sand mass flux and horizontal sand mass flux can be described by a power function. The present study is used to help understand the transport of ascending and descending sand particles. Copyright © 2016 John Wiley & Sons, Ltd.

Strouhal number of bridge cables with ice accretion at low flow turbulence

The paper concerns with the method and results of wind tunnel investigations of the Strouhal number (St) of a stationary iced cable model of cable-supported bridges with respect to different angles of wind attack. The investigations were conducted in the Climatic Wind Tunnel Laboratory of the Czech Academy of Sciences in . The methodology leading to the experimental icing of the inclined cable model was prepared in a climatic section of the laboratory. The shape of the ice on the cable was registered by a photogrammetry method. A section of an iced cable model with a smaller scale was reproduced with a 3D printing procedure for subsequent aerodynamic investigations. The St values were determined within the range of the Reynolds number (Re) between and , based on the dominant vortex shedding frequencies measured in the wake of the model. The model was oriented at three principal angles of wind attack for each of selected Re values. The flow regimes were distinguished for each model configuration. In order to recognize the tunnel blockage effect the St of a circular smooth cylinder was also tested. Good agreement with the reported values in the subcritical Re range of a circular cylinder was obtained. The knowledge of the flow regimes of the airflow around an iced cable and the associated St values could constitute a basis to formulate a mathematical description of the vortex-induced force acting on the iced cable of a cable-supported bridge and could allow predicting the cable response due to the vortex excitation phenomenon.

Wind tunnel investigation on the two- and three-blade Savonius rotor with central shaft at different gap ratio

The Savonius rotor seems to be a promising wind turbine as it not only has the simplest and cheapest design but also is capable of yielding a higher annual energy output at low wind speed than the Darrieus rotor. Moreover, the Savonius rotor can also be used in ventilation systems, for local electricity production, as the start-up device for the Darrieus rotor, and small hydrokinetic turbines operating at low velocity. As a two-blade Savonius rotor suffers from negative average static torque coefficient (ACTS) at some azimuth angles and large-amplitude variation of ACTS, several studies have been conducted in recent years to improve ACTS. The three-blade rotor seems to be a potential candidate for ACTS improvement. However, less research has been done on three-blade rotors with a 180° arc and central shaft at different gap ratios (GRs) for different wind speeds. Therefore, the focus of the present work is to compare the two- and three-blade rotor in terms of ACTS and power coefficient (CP) through a wind tunnel experiment. Results show that the wind speed had a small effect on ACTS. However, negative azimuth angle range is narrowed and the negative azimuth angle range is moved upward as GR increased. Hence, the Savonius rotor with three blades could not only eliminate the negative range of ACTS but also smooth ACTS curves. In terms of the CP, the maximum power coefficient of the two-blade configuration was approximately 1.5 times that of the three-blade configuration. The 1/6 GR test data exhibited the attainment of super performance for all wind speed and blade number.

A smart structure for wind tunnel investigation of a bridge deck’s vortex-induced torsional motion

The paper discusses the design and testing of a smart aeroelastic model of a suspended bridge that allows active regulation of torsional damping through the use of embedded piezoelectric actuators. Depending on test conditions, the structural damping of the model can be adjusted in a fast, precise and repeatable way in order to highlight the effects of the wind interaction. In particular, vortex-induced vibrations are taken into consideration. The main elements of the smart structure (sensors, actuators, control algorithm) have been designed on the basis of a numerical model of the system. Finally the aeroelastic model has been tested in a wind tunnel in different operating conditions and its dynamics have been assessed.

Effect of a pusher propeller on a delta wing

A low speed wind tunnel investigation was conducted to examine the effect of a pusher propeller on a 65 deg sweep delta wing. Two different propeller diameters were evaluated. The data showed that the pusher geometry can cause a delay in vortex breakdown yielding an increase in lift at high angles of attack. Surface pressure measurement showed that the propeller increased suction levels on both the leeward and windward surfaces, limiting lift enhancement. Lift augmentation was observed to favor low advance ratios.

A significant part of the experimental investigations (EI) in wind tunnels (WT) aimed at simultaneous measurement of air pressure at distributed points as in the WT, and aircraft models (AM) and in jet engines. In this regard, the actual problem is creati

A significant part of the experimental investigations (EI) in wind tunnels (WT) aimed at simultaneous measurement of air pressure at distributed points as in the WT, and aircraft models (AM) and in jet engines. In this regard, the actual problem is creation of means and methods for simultaneous measurement of pressure as discussed in the work.The first method. The holes of the selection pressure pneumatic tracks (PT) are connected to the pressure sensor (PS), which are connected to the channels of the measuring system (MS). In this MS apply precision instrumentation programmable filter, communication interface with computer and time measurement for channel ≤40ms. The cost of this MS is high, even for 16 channels measurement interval ≥640ms, which for most of the EI is not acceptable.The second method is the use of electro-mechanical pneumatic switches (EMPS). For example, in EMPS type PS-180/ 300/ 420 continuously rotating the rotor of the switching node with a phase shift connects PT to PS, synchronously with the time of establishment of pressure measurement is performed.The third method is the use of mobile pneumatic modules with interface for the transmission of real-time experimental data (ED) in MS. Such devices, for example, can be up to 16 with the number of measured channels and 256.The proposed unified information-MS (IMS), which can be implemented on different hardware and software platforms (VME, PC/104, MicroPC, etc.).Processing. Is calculated, sorted and stored value of the absolute and relative pressure pulsations of velocity head. Determine the mean value and standard error. Normal distribution was confirmed by ED Pearson criterion at the significance level . Statistical reproducibility of ED is confirmed by the criterion of Cochran, assess the homogeneity and error. Is determined by the Reynolds number based on the physical parameters in the WT. The accuracy of the ED algorithm provides operational control of IMS.The transformation function PS is defined in terms of the polynomial. In difficult cases it is necessary to use D-optimal plans experiment.The coefficients of longitudinal and normal components of aerodynamic force, the coefficient of longitudinal moment, the relative position of the center of pressure, normal and tangential components of aerodynamic forces. The problem is to compute the integral with minimum error. It is recommended to apply the Romberg method.

A wind-tunnel investigation of wind-turbine wakes in yawed conditions

Wind-tunnel experiments were performed to study the performance of a model wind turbine and its wake characteristics in a boundary layer under different operating conditions, including different yaw angles and tip speed ratios. High-resolution particle image- velocimetry (PIV) was used to measure the three velocity components in a horizontal plane at hub height covering a broad streamwise range from upstream of the turbine to the far- wake region. Additionally, thrust and power coefficients of the turbine were measured under different conditions. These power and thrust measurements, together with the highly-resolved flow measurements, enabled us to systematically study different wake properties.The near-wake region is found to have a highly complex structure influenced by different factors such as tip speed ratio and wake rotation. In particular, for higher tip speed ratios, a noticeable speed-up region is observed in the central part of near wake, which greatly affects the flow distribution in this region. In this regard, the behavior of the near wake for turbines with similar thrust coefficients but different tip speed ratios can vary widely. In contrast, it is shown that the mean streamwise velocity in the far wake of the turbine with zero yaw angle has a self-similar Gaussian distribution, and the strength of wake in this region is consistent with the magnitude of the thrust coefficient.With increasing yaw angle, as expected, the power and thrust coefficients decrease, and the wake deflection increases. The measurements also reveal that, in addition to turbulent momentum flux, lateral mean momentum flux boosts the flow entrainment in only one side of the wake, which results in a faster wake recovery in that side. It is also found that the induced velocity upstream of a yawed turbine has a non-symmetric distribution, and its distribution is in agreement with the available model in the literature. Moreover, the results suggest that in order to accurately predict the load distribution in yawed conditions, both normal and tangential (with respect to the rotor plane) components of the induced velocity upstream of the turbine should be taken into account.

Influence of drift angle on the computation of hull–propeller–rudder interaction

The operation of the propeller dominates the flow interaction effects on the upstream hull and a downstream rudder. An investigation is carried out into the sensitivity with which these effects can be resolved when an angle of drift is applied as well as the length of an upstream body is varied. The computed results are compared to a detailed wind tunnel investigation which measured changes in propeller thrust, torque and rudder forces. Variation of the upstream body length and drift angle effectively varies the magnitude of the crossflow and wake at the propeller plane. The time resolved flow was computed around the hull–propeller–rudder configuration using the Reynolds-averaged Navier–Stokes (RANS) equations and an Arbitrary Mesh Interface (AMI) model to account for the motion of the propeller. A mesh sensitivity study quantifies the necessary number of mesh cells to adequately resolve the flow field. Overall, good agreement is found between the experimental and computational results when predicting the change in propulsive efficiency, flow straightening and rudder manoeuvring performance. However, it can be seen that there is a significant computational expense associated with a time resolved propeller interaction and that alternative body force based methods are likely to still be required with the computation of self-propelled ship manoeuvres.

A Holistic Approach for Low Cost Heliostat Fields

The AutoR-project takes a holistic approach to reduce the cost of heliostat fields: Wireless control and energy supply enables to use smaller heliostats which need less steel per mirror area (but usually have high wiring cost). A low cost but high efficient drive system is chosen which reduces energy consumption to a minimum amount and leads to low cost for PV cell and energy storage. The usual boundary layer wind tunnels tests for heliostats are proven regarding energy spectra to avoid oversizing of steel structure and drives or failures because of underestimations of the loads. The concepts for wireless control and energy supply, the wind tunnel investigations and the first rim drive heliostat prototype are presented.

Wind tunnel investigation of sound attenuation in turbulent flow

Wind tunnel investigation of the sound wave attenuation by grid-generated turbulence is performed. The most influential parameters, such as the propagation distance, intensity of turbulent fluctuations and integral scale of the fluctuations are studied using an ultrasonic technique. The results are compared to the theoretical predictions available on the wave statistics. Theoretical predictions are well confirmed and partly extended. It is demonstrated that the ultrasonic technique provides the possibility of reproducing the main effects of atmospheric turbulence on sound propagation while benefiting from isolating the role of various parameters therefore sets of experimental data can be generated under laboratory conditions to benchmark further extensions of theoretical models and numerical simulations.

Effect of Taper Ratio at Low Reynolds Number

A low speed wind-tunnel investigation is presented documenting the impact of taper ratio at low Reynolds number. An wing using a S8036 section was tested at and 150,000. Taper ratio was varied from 1 down to 0.2 in 0.2 increments. An analytic prediction method as well as extended numerical lifting line theory incorporating nonlinear section data was implemented to compare with experiment. The experimental results indicated a weak dependence of peak lift to drag ratio on taper ratio for both Reynolds numbers. Surface flow visualization showed the presence of a large laminar transitional bubble on the upper wing surface. The relative extent of the bubble was observed to increase towards the tip region for tapered planforms. Agreement between theory and experiment in terms of lift and drag estimation was good. Planform optimization using the extended numerical lifting line theory indicated that at the test conditions and using the selected airfoil section, a planform that differs from straight taper or elliptic may be most efficient.

STUDY OF DRUG FORCE AND THE FLOW FIELD ON ROAD VEHICLES Khalid M. Sawoud

Improving road vehicles performance needs to deep understanding the science of aerodynamics, in order to control flow field by means of active and passive control techniques. The airflow behavior when passes over the road vehicles surfaces will be changes in patterns and resulting in different pressure regions. This pressure region causes drag force and thereby increases in fuel consumption of the road vehicles. This paper include experimental study to investigate the effect of road vehicles for three most common rear end configurations design such as (square, notch and fastback) on drag force, drag coefficient and pressure distribution. The experiments were carried out an open, low speed, and three dimensional wind-tunnel, on geometrical similarity to the prototype (Audi 80 1987) in scale down (1:18) wooden models for four different velocities (11.31, 13.86, 17.89 and 22.98) m/sec. The results obtained from the wind-tunnel investigations showed that the drag force increases with the increasing of free-stream velocities. The minimum drag coefficient can be achieved with fastback configuration, comparing with the other tested models and result in approximately 16% and 48% lower than that for notch and square back configurations, respectively. These results are demonstrated by the pressure distribution curves which provide a deep understanding of the flow behavior above the tested models.

Buffeting Wind Load on Antennas with Rooftop Site

Most of the mobile phone antennas are located in urban areas. An economical solution is to place the antennas on top of existing buildings. In practice, any effect that the building has on the antenna wind load is neglected. Wind tunnel investigations and numerical simulations show that the wind loading might increase in some cases by up to 30% compared with the free flow.

A wind tunnel investigation into the effects of roof curvature on the aerodynamic drag experienced by a light goods vehicle

Roof curvature is used to increase ground vehicle camber and enhance rear–body boat–tailing to reduce aerodynamic drag. Little aerodynamic data is published for light goods vehicles (LGVs) which account for a significant proportion of annual UK licensed vehicle miles. This paper details scale wind tunnel measurements at Re = 1.6 × 106 of a generic LGV utilising interchangeable roof panels to investigate the effects of curved roof profile on aerodynamic drag at simulated crosswinds between −6° and 16°. Optimum magnitudes of roof profile depth and axial location are suggested and the limited dataset indicates that increasing roof curvature is effective in reducing drag over a large yaw range, compared to a flat roof profile. This is primarily due to increased base pressure, possibly from enhanced mixing of longitudinal vortices shed from the rear–body upper side edges and increased turbulent mixing in the near–wake due to the increased effective boat–tail angle.