Comparative Studies between CFD and Wind Tunnel Measurements of Cooling Performance and External Aerodynamics for a Heavy Truck

Abstract

Reducing the harmful effect of vehicles on the environment is a key question for vehicle manufacturers today. Constantly increasing oil prices and stricter emission legislations are also important factors for the vehicle industry to consider. There are many factors affecting the fuel consumption of a vehicle. One of the major ones is the aerodynamic resistance. In fact, above 80km/h, the aerodynamic drag is the most significant resistance for a truck driving at constant speed, according to Lögdberg [1]. Hence the importance of working with the aerodynamic properties of trucks is apparent.Cooling drag is a part of the total aerodynamic drag, arising as a consequence of air flowing through the grille, cooling module and the irregular under-hood area. Hallberg [2] states that the trend is towards more and more cooling being required, not only as a consequence of increased engine power, but also for ABSTRACT Nowadays, much focus for vehicle manufacturers is directed towards improving the energy efficiency of their products. The aerodynamic drag constitutes one major part of the total driving resistance for a vehicle travelling at higher speeds. In fact, above approximately 80km/h the aerodynamic drag is the dominating resistance acting on a truck. Hence the importance of reducing this resistance is apparent. Cooling drag is one part of the total aerodynamic drag, which arises from air flowing through the heat exchangers, and the irregular under-hood area.When using Computational Fluid Dynamics (CFD) in the development process it is of great importance to ensure that the methods used are accurately capturing the physics of the flow. This paper deals with comparative studies between CFD and wind-tunnel tests.In this paper, two comparative studies are presented. One is a comparison between cooling performance simulations and chassis dynamometer measurements; the other study is a comparison between external aerodynamics simulations and wind-tunnel measurements.The purpose of this study was to evaluate and develop methods and models for determining aerodynamic drag and cooling performance, which ultimately will be used to develop more energy-efficient cooling of heavy trucks.The results from the two comparative studies showed that there was in general good agreement between CFD and wind-tunnel measurements. For the cooling performance simulations, the analysed parameters were very close to the measured values. For the external aerodynamics simulations, the results were not easy to analyse. The overall results were still satisfactory; for the simulated yaw angles, the drag coefficient (C D ) values were less than 4.1% different from measured data.

Influence of Rotating Wheels and Moving Ground Use on the Unsteady Wake of a Small-Scale Road Vehicle

“…For the current setup, this was chosen atypically small (0.13 W) to minimise any likelihood of significant flow unsteadiness, not related to the wake flow, developing and degrading load cell signal quality. With such a small gap however, lower pressures are known to develop in this region producing two similar, but opposing effects: increased tractor drag due to exposure to its back surface, and reduced trailer drag from exposure to its front face (Martini et al 2014;Pankajakshan et al 2016). Frank and Turney (2016) also show this effect can be significant, with a trailer absent any undercarriage/wheel contributions (similar to the current setup) being an overall negative contributor to total drag.…”

“…However, many details of how, if at all, these processes are affected by such additions continue to remain unresolved. This is particularly evident for tests performed at high model solid blockage ratios characteristic to many previous HGV investigations (Britcher et al 2014;Leuschen 2013;Martini et al 2014;Stephens and Babinsky 2016;Storms et al 2001).…”

“…One of many factors can account for this result. Martini et al (2014), McCallen et al 2000, Frank and Turney (2016), and Pankajakshan et al 2016all highlight a strong dependence of tractortrailer gap on trailer drag. For the current setup, this was chosen atypically small (0.13 W) to minimise any likelihood of significant flow unsteadiness, not related to the wake flow, developing and degrading load cell signal quality.…”

Upstream wind tunnel model mounting: The forgotten method for road vehicle aerodynamics

“…In such a configuration, lower surface pressures are known to act on the trailer front, promoting reduced trailer-alone drag results. [60][61][62] Also shown in Table 3 is trailer drag being larger for the top mounting (C DT ' 0.017) in comparison to the side (C DT ' 0.011) and front (C DT ' 0.006) setups. These changes are very subtle, with all lying within the experimental uncertainty (60.010).…”

Numerical investigation and experimental test on aerodynamic noises of the bionic rear view mirror in vehicles

“…For example, wind tunnel experiments require very high cost and long experimental time, so that repeatability of experimental results is not high, and collection of experimental data is greatly limited. Secondly, computer simulation technologies are used for numerical simulation [15][16][17]. Numerical simulation technologies could select any structural parameter of a studied object to conduct in-depth researches, and have good computational effects.…”