Kevin R. Cooper

Correction of distortion effects caused by tubing systems in measurements of fluctuating pressures

Abstract Methods of reducing and correcting for the distortion effects introduced by pressure tubing systems in measurements of fluctuating pressures are discussed. A new technique is described, involving a digital correction technique using the known tubing transfer function. It allows considerably longer tubes and higher frequency response to be obtained than with other methods, and furthermore, phase distortion is effectively eliminated. The simpler technique of inserting restrictors in tubing systems is evaluated and found to reduce the distortion to acceptable levels for short tube lengths.

Truck Aerodynamics Reborn - Lessons from the Past

During the late 1970s and early 1980s considerable effort was expended in the improvement of truck aerodynamics to reduce fuel consumption. This first-generation effort focused on aerodynamic drag reduction obtained from add-on aerodynamic aids to the cab or the trailer, from improved cab shaping and from body/trailer front-end edge rounding. Rising fuel prices have renewed interest in further aerodynamic improvements. This paper will review past developments and show that several unused concepts offer potential as second-generation, add-on, fuel-saving technology. It will raise the issue of finding successful means for bringing them profitably into service, which will require concerted action by the trucking industry, manufacturers and government.

Windthrow in riparian buffer strips: effect of wind exposure, thinning and strip width

This paper discusses the effects of topography, riparian buffer strip width and thinning on the amount of windthrow over 9 years in balsam fir (Abies balsamea) stands. Monitoring of windthrow was conducted in 25 riparian areas representing five treatments: uncut control, thinned 20 m strip, unthinned 20, 40 and 60 m strips. Wind tunnel measurements were made on a topographical model of the study area to provide an estimate of local wind behaviour. A cluster analysis performed on the wind speed data led to the identification of four major topographic units of similar wind behaviour. Wind speed in valleys varied greatly depending upon the direction of the approaching winds and the presence of small topographic features. When the wind blows perpendicularly to the valley, wind speed tends to be lower but more variable than when it blows parallel to the valley. Windthrow was not related to strip width or thinning. The field study showed that windthrow 5 years after cutting was found to be correlated with the speed of winds blowing roughly perpendicular to the strips. Windthrow after 7 and 9 years, following an unusual wind event that occurred between years 5 and 7, was no longer correlated with this wind direction. High levels of damage were observed where the valley widened, offering less shelter to the buffer strips.

THE EFFECT OF FRONT-EDGE ROUNDING AND REAR-EDGE SHAPING ON THE AERODYNAMIC DRAG OF BLUFF VEHICLES IN GROUND PROXIMITY

Wind tunnel measurements on a rectangular vehicle-like shape and on two detailed, scale-model trucks have been employed to define the front and rear edge geometries that minimize aerodynamic drag. Optimum configurations are identified with sufficient detail for commercial vehicle design purposes. Comparisons of the model-scale measurements with limited measurements on a full-scale straight truck in a large wind tunnel support the interpretation of these test results.

Dual luminophor pressure-sensitive paint: III. Application to automotive model testing

Porphyrins play key roles in natural energy conversion systems, including photosynthesis and oxygen transport. Because of their chemical stability, unique optical properties and synthetic versatility, porphyrins are well suited as chemical sensors. One successful application is the use of platinum porphyrin (PtP) in pressure-sensitive paint (PSP). Oxygen in the film quenches luminescence, and oxygen pressure was initially monitored by measuring the ratio of I(wind-off)/I(wind-on). But this ratio is compromised if there is model motion and if the paint layer is inhomogeneous. Furthermore it requires careful monitoring and placement of light sources. Moreover, this method is seriously affected by temperature. The errors caused by model motion and temperature sensitivity are eliminated or greatly reduced using dual luminophor paint. This paper illustrates a successful application of a dual luminophor PSP in auto model testing. The PSP is made from an oxygen sensitive luminophor, Pt tetra(pentafluorophenyl)-porpholactone, which provides Isen, and Mg tetra(pentafluorophenyl)porphine, which provides temperature-sensitive paint (TSP) as the pressure-independent reference. The ratio PSP/TSP in the FIB polymer produced ideal PSP measurements with a very low-temperature dependence of −0.1% °C−1.

Full-Scale Wind Tunnel Tests of Production and Prototype, Second-Generation Aerodynamic Drag-Reducing Devices for Tractor-Trailers

The National Research Council of Canada (NRC) has completed the second round of full-scale wind tunnel tests on Class-8 tractor-trailer combinations. The primary intent of the program is to effect a reduction in greenhouse-gas emissions by reducing the fuel consumption of trucks through aerodynamic drag reduction. Add-on aerodynamic components developed at the NRC several decades ago have become important contenders for drag reduction. This program has encouraged the commercialization of these technologies and this round of tests evaluated the first commercial products. Three primary devices have been evaluated, with the combination able to reduce fuel consumption by approximately 6,667 liters (1,761 US gal) annually, based on 130,000 km (81,000 miles) traveled per tractor at a speed of 100 km/hr (62 mi/hr).

Comparison of quasi-static and dynamic wind tunnel measurements on simplified tractor-trailer models

Abstract The results from a series of wind tunnel experiments are presented, intended to measure dynamic forces and moments on simplified commercial vehicle type models rotating about their vertical centre line axis in smooth, uniform flow. These results are compared with quasi-static measurements on the same models over a range of fixed yaw angles (the conventional technique for wind tunnel test on this type of vehicle) in order to assess the significance of attempting to simulate the essentially dynamic nature of the full scale flowfield in a wind tunnel. It is shown that the magnitude of drag and yawing moment coefficients do not change significantly even at rotational rates as high as 64° s −1 . However the dynamic coefficient versus yaw angle curves appear displaced, relative to the yaw angle axis, compared to the static data. The magnitude and sign of this “phase shift” are seen to be dependent on both yaw rate and model geometry and are evident at rotational rates as low as 0.25° s −1 .

Bluff-body aerodynamics as applied to vehicles

Abstract This paper discusses the aerodynamics of surface vehicles viewed as bluff or quasi-bluff bodies from the perspective of the wind tunnel practitioner. It summarizes current wind tunnel techniques and illustrates the broad range of contemporary applications through examples drawn primarily from the authors experience.

An examination of the effects of wind turbulence on the aerodynamic drag of vehicles

Abstract Data from wind-tunnel and full-scale measurements of the aerodynamic drag on trucks are used to illustrate the effects of wind turbulence. An attempt has been made to estimate these effects using a quasi-steady average of smooth-flow wind-tunnel data, allowing the data to be adjusted to better represent road conditions. The theory does not completely explain the behaviour observed in turbulence conditions although some of the general trends found in turbulent-flow wind-tunnel tests are predicted.

Unsteady aerodynamic force measurements on a super-tall building with a tapered cross section

The unsteady wind loads acting on a super-tall building with a tapered cross section and beveled corners were measured as functions of reduced velocity and motion amplitude. The model amplitude was controlled by an hydraulic actuator and the unsteady sectional aerodynamic loads were measured using manifolded pressure taps. The damping components of the along-wind and cross-wind unsteady aerodynamic forces were obtained from the time histories of fluctuating aerodynamic force. The vertical distribution of damping component dependent on amplitude and reduced frequency are discussed. The obtained aeroelastic damping is compared with those from aeroelastic response measurement and those predicted by quasi-steady theory.