Wind Tunnel Procedure Research Articles

Aerodynamic Model Updating Using Wind-Tunnel Setup for Hummingbirdlike Flapping Wing Nanorobot

The complex wing motion of insects and small birds leads to high lift production in nature. Specific lift-enhancing mechanisms arise from the combination of a horizontal stroke motion and a secondary wing pitching motion. Research around flapping wing nano air vehicles (FWNAVs) copies this wing motion to fly small drones, in an effort to benefit from the same mechanisms. A flapping wing aerodynamic model can predict the force production of the FWNAV and helps to understand the influence of the wing kinematics thereon. This work starts from a quasi-steady model expression for the aerodynamics and proposes a wind-tunnel procedure to identify the force coefficients in the model empirically. The procedure is based on a test case performed by the AVT-202 research team that combines wing translation and wing rotation, imitating the aerodynamic condition of the flapping wing in a simplified setup. Comparison of measurements and model simulations demonstrates that the procedure can be used to update the model parameters for our specific FWNAV configuration, leading to an empirical relation for the force coefficients. Simulations with the updated model using the empirical relations show good agreement with measured force production for a wide range of input variables.

Wing-in-ground-effect craft: A case study in aerodynamics

A wing-in-ground-effect (WIGE) crafts can be deployed to fly by utilizing the ground effect, which is a natural phenomenon known to improve the efficiency of airplanes during take-off and landing approaches. In contrast, WIGE craft is not commercially viable for public transport mainly due to the difficulties in controlling its longitudinal stability. As an attempt to support the development of WIGE crafts, this paper presents a case study in aerodynamics based on certain published reports, specifically to reveal the available research data that are considered of interest and can be used as a lesson for further study and analysis. The wind tunnel procedure and testing, as well as numerical investigation of a WIGE craft, are applied and the results are then analyzed. The discussions are oriented in the perspectives of aerodynamics. Based on the tests and calculation, parameters concerning the ground effect as the WIGE crafts approaching the ground surfaces may be identified and hence their values can be determined. Thus, the static longitudinal stability may then be established and optimized for control of the WIGE craft.

Wind Load Factors for Use in the Wind Tunnel Procedure.

A 2004 Skidmore Owings and Merrill report (in Simiu E. (2011) Design of Buildings for Wind, Appendix 5, Wiley, Hoboken, NJ) notes that the ASCE 7 Standard (American Society of Civil Engineers (2002) ASCE 7-02, Reston, Va) is incomplete insofar as it provides no guidance on wind load factors appropriate for use with the Standard's wind tunnel procedure. The purpose of this paper is to contribute to such guidance. Based on a classical definition of wind load factors as functions of uncertainties in the micrometeorological, wind climatological, aerodynamics and structural dynamics elements that determine wind loads, the paper presents a simple, straightforward approach that allows practitioners to use appropriate wind load factors applicable when those uncertainties are either the same as or different from those assumed in the development of the ASCE 7 Standard. Illustrations of the approach are presented for a variety of cases of practical interest. In estimating design wind loads, the various uncertainties should not be accounted for in isolation, for example by specifying peak pressure coefficients with percentage points higher than those corresponding to their expected values. Rather, to achieve risk-consistent designs, the uncertainties should be accounted for collectively, in terms of their joint effect on the design wind loading. The design wind effect is equal to the estimated expectation of the peak wind effect times a load factor that, in most cases, is not significantly different from the load factor explicitly or implicitly specified in the ASCE 7 Standard. Notably, the load factor is not affected significantly by errors associated with interpolations required in typical Database Assisted Design applications. However, if the available wind speed records are several times shorter than, say, 20 to 30 years, the wind load factors increase by amounts of the order of 15 %.

Advances in the design of high-rise structures by the wind tunnel procedure: Conceptual framework

This paper surveys and complements contributions by the National Institute of Standards and Technology to techniques ensuring that the wind tunnel procedure for the design of high-rise structures is based on sound methods and allows unambiguous inter-laboratory comparisons. Developments that enabled substantial advances in these techniques include: Instrumentation for simultaneously measuring pressures at multiple taps; time-domain analysis methods for estimating directional dynamic effects; creation of large simulated extreme directional wind speed data sets; non-parametric methods for estimating mean recurrence intervals (MRIs) of Demand-to-Capacity Indexes (DCIs); and member sizing based on peak DCIs with specified MRIs. To implement these advances changes are needed in the traditional division of tasks between wind and structural engineers. Wind engineers should provide large sets of directional wind speeds, pressure coefficient time series, and estimates of uncertainties in wind speeds and pressure coefficients. Structural engineers should perform the dynamic analyses, estimates of MRIs of wind effects, sensitivity studies, and iterative sizing of structural members. The procedure is transparent, eliminates guesswork inherent in frequency domain methods and due to the lack of pressure measurements, and enables structural engineers to be in full control of the structural design for wind.

Assessment of ASCE 7-10 Standard Methods for Determining Wind Loads

The purpose of this paper is to discuss issues associated with ASCE 7-10 standard methods for determining wind loads on buildings and other structures that warrant comment, correction, or improvement. The assessment is intended to serve as a resource in the development of a new version of the ASCE 7 standard and to stimulate a wider participation in that development by the structural engineering community. Issues discussed in the paper include: wind speeds in nonhurricane regions; alternative analytical methods for determining wind loads and wind effects on main wind force resisting systems and components and/or cladding; aerodynamic pressure coefficients; pressures on rooftop equipment; component and cladding pressures on arched roofs; and the wind tunnel procedure. It is noted that the ASCE 49 standard essentially covers wind tunnel testing, rather than the wind tunnel procedure, of which wind tunnel testing is only a part.

Factors Influencing the Performance of Spray Delivery Systems: A Review of Recent Developments

Abstract The need for designers and users of pesticide application equipment to balance the risk of off-target contamination with high product efficacies when using the minimum dose of active ingredient has led to the requirement for more data defining the performance of such equipment. Measurements of the droplet size distribution in sprays from conventional nozzles has shown acceptable levels of consistency between data obtained with different measuring systems enabling such sprays to be classified providing that systems are calibrated with agreed reference nozzles. For sprays with air inclusions different measuring systems have been shown to give comparable and consistent results, and there is now a need to fully integrate such sprays into a revised classification scheme. Temperature of both spray liquid and the surrounding air have been shown to influence droplet size distribution measurements. It is therefore proposed that measurement protocols specify a maximum difference in temperature between the spray liquid and surrounding air of 5°C. For boom sprayers it is not possible to predict accurately the risk of drift from droplet size measurements alone because of the complex detrainment mechanisms involved. It is proposed that standardized wind tunnel procedures be defined that enable the relative risk of drift from different nozzle designs to be quantified. In the future it is likely that more of the information relating to application system performance will be delivered pre-programmed in the units control system or as part of a decision support system.

Aeroelastic analysis of bridges using FEM and moving grids

In the recent years flow around bridges are investigated using computer modeling. Selvam (1998), Selvam and Bosch (1999), Frandsen and McRobie (1999) used finite element procedures. Larsen and Walther (1997) used discrete vorticity procedure. The aeroelastic instability is a major criterion to be checked for long span bridges. If the wind speed experienced by a bridge is greater than the critical wind speed for flutter, then the bridge fails due to aeroelastic instability. Larsen and Walther (1997) computed the critical velocity for flutter using discrete vortex method similar to wind tunnel procedures. In this work, the critical velocity for flutter will be calculated directly (free oscillation procedure) similar to the approaches reported by Selvam et al. (1998). It is expected that the computational time required to compute the critical velocity using this approach may be much shorter than the traditional approach. The computed critical flutter velocity of 69 m/s is in reasonable comparison with wind tunnel measurement. The no flutter and flutter conditions are illustrated using the bridge response in time.

Stream Path and Similarity

This report is a commentary description of the foremost article “Exhartaiion for Measurement of Stream Path” on Wind engineers, JAWE No.87, and consists of the data analysis of wind pressure measurements in natural winds and the consideration of Reynolds number problem. The conception of the stream path obtained by the time integration of the wind velocity vector at the one spatial point has it significant roll for giving the geometric condition of the similarity. The curvature of the stream path produces the circulation around the obstacle in dynamic sense of the flow pattern generation. The circulation causes the lateral forte by the different mechanism from the static flow pattern due to the straight stream. The operation of viscous stress suppresses for the usual wind tunnel procedure to follow the change ofthe flow pattern induced by the curved stream path in turbulent flow

Field and Wind Tunnel Measurements of the Airborne Spray Volume Downwind of Single Flat-Fan Nozzles

Considerable effort is now being directed at using wind tunnel approaches to define the risk of drift from nozzle systems mounted on boom sprayers. The work reported here assesses the level of agreement that is likely to be obtained in such wind tunnel procedures through investigation using a simplified single-nozzle arrangement. The airborne spray volume 2·0 m downwind from two sizes of a single flat-fan nozzle was measured in field conditions and the results compared with those obtained from similar experiments conducted with two different wind tunnel configurations. Results from the field tests were also compared with predictions from a computer simulation model.Airborne spray volume measured downwind of the nozzles in field conditions was shown to increase approximately linearly with increasing wind speed as expected. The measurements of total drift in the wind tunnel reproduced the form of equivalent field results. Vertical profiles of airborne spray volume measured in both the field and wind tunnel experiments at nominal cross-wind speeds of 2·0 and 3·0 m/s appeared relatively insensitive to the vertical profile of the mean wind. Results from the computer simulation model also gave a reasonable description of the form of the airborne spray volume profiles, but the total quantity of drifting spray was under-predicted by the model by a factor of between two and three.

Wind direction and hurricane-induced ultimate wind loads

A consensus on the wind directionality issue is needed for the validation by building officials of the wind-tunnel procedure allowed by the ASCE 7-95 Standard, and for the development of provisions for wind loads that use large aerodynamic and climatological databases. As a contribution to the debate needed to achieve such a consensus, we describe an updated method for estimating wind loads that takes into account the directional dependence of the aerodynamic coefficients and the extreme wind climate, and uses the `peaks over threshold' approach for the estimation of extremes. For hurricane-prone regions, assuming epistemic uncertainties are negligible, we estimate mean recurrence intervals (MRIs) of wind loads inducing the design strength, obtained from 50 yr loads via multiplication by a factor specified by the ASCE 7-95 Standard. For typical aerodynamic coefficients with strong directional preference, depending upon location and building orientation those estimated MRIs varied between less than 1000 to more than 10 000 yr. If epistemic uncertainties were taken into account the estimated MRIs would be shorter. We also found that for loads with very large MRIs the common practice of disregarding direction effects is not necessarily conservative from a structural engineering viewpoint.

The Silsoe Structures Building: Comparisons of pressures measured at full scale and in two wind tunnels

Two independent sets of full-scale wind pressure measurements have been completed on the Silsoe Structures Building in both its configurations (featuring a conventional sharp eaves and a modern curved eaves). Results are compared with those from two 1 : 100 scale measurement programmes conducted in two leading wind tunnels on models of the building with both the sharp and curved eaves. These comparisons highlight the importance of implementing certain wind tunnel procedures in order to obtain good predictions of full-scale mean pressure coefficients. However, areas of high negative pressure still tend to be under-estimated in wind-tunnel measurements and this is considered to be associated with a Reynolds number effect.

The validity of sectional models on wind tunnel tests for vortex induced oscillation of bridges

The validity of wind tunnel procedure with sectional models used to investigate the aerodynamic stability of long-span bridges was examined by several wind tunnel tests. The vortex induced bending oscillations of some rectangular cylinders were discussed comparing the bending amplitudes, aerodynamic forces, surrounding flow patterns and unsteady pressure distributions of the sectional models with those of the taut strip models. After that, it becomes clear that there is a significant difference between the responses of 2D and 3D models for the reason of the non-linear dependence of unsteady aerodynamic force on amplitude and the existence of spanwise flow.

Wind Load Provisions Ansi #A58.1‐1982

The wind load provisions of ANSI A58.1, published in 1982, contain the latest available pertinent data and technical knowledge. Summary of changes from the previous standard and background material for wind speed map, format of the standard, importance coefficient, pressure coefficients, and wind tunnel procedure are presented. The balloting and public review process has resulted in a consensus standard.

Sting-free drag measurements on ellipsoidal cylinders at transition Reynolds numbers

The drag coefficient for a family of axially symmetric ellipses of fineness ratio 4, 5 and 8 was measured using magnetically suspended models. The Reynolds number ranged up to 106. Thus, only the blockage interference is present, which may be partially allowed for by classical wind tunnel procedures. It is expected that the drag values presented here are accurate to 1%.