Search Results

This paper presents pressure drops and heat transfer rates for compact heat exchangers, where the heat exchangers are angled 90°, 60°, 30° and 10° relative to the incoming airflow. The investigation is based on three heat exchangers with thicknesses of 19mm and 52mm. Each heat exchanger was mounted in a duct, where it was tested for thermal and isothermal conditions. The inlet temperature of the coolant was defined to two temperatures; ambient temperature and 90°C. For the ambient cases the coolant had the same temperature as the surrounding air, these tests were performed for five airflow rates. When the coolant had a temperature of 90°C a combination of five coolant flow rates and five airflow rates were tested. The test set-up was defined as having a constant cross-section area for 90°, 60° and 30° angles, resulting in a larger core area and a lower airspeed through the core, for a more inclined heat exchanger.

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.

This article presents Computational Fluid Dynamics (CFD) simulations fo one period of a louvered fin, for a crossflow compact finned heat exchanger, where the incoming airflow was inclined relative to its core. Four inclinations were investigated: 90°, which was when the air flowed perpendicular to the heat exchanger, 60°, 30° and 10° angles relative to the vertical plane. The study included three heat exchanger designs, where two of them had symmetrical louvered fins and a thickness of 19mm and 52mm. The third had a thickness of 19mm and had the louvers angled in one direction. All heat exchangers have been simulated when the airflow entered both from above and below relative to the horizontal plane. Simulations have also been carried out when the airflow entered from the side, illustrating the heat exchanger to be angled relative to the vertical axis. Two air speeds have been investigated for each configuration, where the results were compared to experimental data.

Quantification of heat exchanger performance in its operative environment is in many engineering applications an essential task, and the air flow rate through the heat exchanger core is an important optimizing parameter. This paper explores an alternative method for quantifying the air flow rate through compact heat exchangers positioned in the underhood of a passenger car. Unlike conventional methods, typically relying on measurements of direct flow characteristics at discrete probe locations, the proposed method is based on the use of load-cells for direct measurement of the total force acting on the heat exchanger. The air flow rate is then calculated from the force measurement. A direct comparison with a conventional pressure based method is presented as both methods are applied on a passenger car’s radiator tested in a full scale wind tunnel using six different grill configurations. The measured air flow rates are presented and discussed over a wide range of test velocities.

Wheel and underbody aerodynamics have become important topics in the search to reduce the aerodynamic drag of the heavy trucks. This study aims to investigate, experimentally as well as numerically, the local flow field around the wheels and in the wheel housing on a heavy truck; and how different approaches to modelling the wheel rotation in CFD influences the results. Emphasis is on effects due to ground simulation, and both moving ground and wheel rotation were requirements for this study. A 1:4-scale model of part of a heavy truck geometry has been developed. During the model design numerical simulations were used to optimise the shape, in order to replicate the flow field near the wheel of a complete truck. This was done by changing the flow angles of the incoming and exiting flows, and by keeping the mass flow rates in to, and out of, the wheel housing at the same ratios as in a reference full size vehicle.

Constantly lowering emissions legislation and the fact that fuel prices have increased tremendously over recent years, have forced vehicle manufacturers to develop more and more energy-efficient vehicles. The aerodynamic drag is responsible for a substantial part of the total driving resistance for a vehicle, especially at higher velocities; thus it is important to reduce this factor as much as possible for vehicles commonly operating in these conditions. In an attempt to improve transport efficiency, longer vehicle combinations are becoming more common. By replacing some of the shorter vehicle combinations with longer combinations, the same amount of cargo can be transported with fewer vehicles; hence there is large potential for fuel savings. The knowledge of the aerodynamic properties of such vehicles is somewhat limited, and therefore interesting to study.

Passenger car fuel consumption is a constant concern for automotive companies and the contribution to fuel consumption from aerodynamics is well known. Several studies have been published on the aerodynamics of wheels. One area of wheel aerodynamics discussed in some of these earlier works is the so-called ventilation resistance. This study investigates ventilation resistance on a number of 17 inch rims, in the Volvo Cars Aerodynamic Wind Tunnel. The ventilation resistance was measured using a custom-built suspension with a tractive force measurement system installed in the Wheel Drive Units (WDUs). The study aims at identifying wheel design factors that have significant effect on the ventilation resistance for the investigated wheel size. The results show that it was possible to measure similar power requirements to rotate the wheels as was found in previous works.

Targets for reducing emissions and improving energy efficiency present the automotive industry with many challenges. Passenger cars are by far the most common means of personal transport in the developed part of the world, and energy consumption related to personal transportation is predicted to increase significantly in the coming decades. Improved aerodynamic performance of passenger cars will be one of many important areas which will occupy engineers and researchers for the foreseeable future. The significance of wheels and wheel housings is well known today, but the relative importance of the different components has still not been fully investigated. A number of investigations highlighting the importance of proper ground simulation have been published, and recently a number of studies on improved aerodynamic design of the wheel have been presented as well. This study is an investigation of aerodynamic influences of different tires.

During the development of the aerodynamic properties of fore coming road vehicles down scaled models are often used in the initial phase. However, if scale models are to be utilised even further in the aerodynamic development they have to include geometrical representatives of most of the components found in the real vehicle. As the cooling package is one of the biggest single generators of aerodynamic drag the heat exchangers are essential to include in a wind tunnel model. However, due mainly to limitations in manufacturing techniques it is complicated to make a down scaled heat exchanger and instead functional dummy heat exchangers have to be developed for scaled wind tunnel models. In this work a Computational Fluid Dynamics (CFD) code has been used to show that it is important that the simplified heat exchanger model has to be of comparable size to that of the full scale unit.

A common fan model to use in automotive under hood simulations is the Multiple Reference Frame (MRF) model and within the industry, for this specific application, this model is well known to under predict performance. In this paper we have examined the possibilities of correcting this deficiency with a simple “speed correction”. This is done by testing and simulating a production fan in the Volvo Fan Test Rig for two operating speeds, 1200 rpm and 2400 rpm. Pressure rise, fan power and static efficiency are presented as functions of volumetric flow rate. The simulations verify that using the MRF model the common behavior of under predicting pressure rise and performance of the fan occur. In addition, this work shows that; although the MRF is not predicting fan performance correctly it constitutes a reliable fan modeling strategy.

Automotive wind tunnel testing is a key element in the development of the aerodynamics of road vehicles. Continuous advancements are made in order to decrease the differences between actual on-road conditions and wind tunnel test properties and the importance of ground simulation with relative motion of the ground and rotating wheels has been the topic of several studies. This work presents a study on the effect of active ground simulation, using moving ground and rotating wheels, on the aerodynamic coefficients on a passenger car in yawed conditions. Most of the published studies on the effects of ground simulation cover only zero yaw conditions and only a few earlier investigations covering ground simulation during yaw were found in the existing literature and all considered simplified models. To further investigate this, a study on a full size sedan type vehicle of production status was performed in the Volvo Aerodynamic Wind Tunnel.

The most common fan model to use in commercial CFD software today is the Multiple Reference Frame (MRF) model. This is at least valid for automotive under hood applications. Within the industry, for this typical application, this model is commonly known to under predict performance. This under prediction has been documented by the authors' of this paper in SAE paper 2009-01-0178 and VTMS paper 2009-01-3067. Furthermore has this been documented by S.Moreau from Valeo in “Numerical and Experimental Investigation of Rotor-Stator Interaction in Automotive Engine Cooling Fan Systems”, ETC, 7th European Conference on Turbomachinery, 2007. In preceding papers a specific methodology of use has been documented and it has been shown that the MRF model under predicts performance for the airflow in a cooling system commonly with 14% in volumetric flow rate. This is for a system dominated by inertial effects.

The aim of the study was to investigate the cooling performance of two cooling package positions for distribution vehicles by using Computational Fluid Dynamics. The first cooling package was positioned in the front of the vehicle, behind the grill and the second position was at the rear of the vehicle. Each case was evaluated by its cooling performance for a critical driving situation and its aerodynamic drag at 90 km/h, where the largest challenge of an alternative position is the cooling air availability. The geometry used was a semi-generic commercial vehicle, based on a medium size distribution truck with a heat rejection value set to a fixed typical level at maximum power for a 13 litre Euro 6 diesel engine. The heat exchangers included in the study were the air conditioning condenser, the charge air cooler and the radiator. It was found that the main problem with the rear mounted cooling installation was the combination of the fan and the geometry after the fan.

The aim with this investigation was to study the aerodynamic properties of truck-trailer combinations of varying lengths. The aerodynamic properties of the combinations were evaluated in order to study similarities and differences in the flow field between different configurations. By the use of Computational Fluid Dynamics (CFD) six different types of truck-trailer combinations used for long hauling have been evaluated. The combinations have a total length varying between 10.10 m and 25.25 m and consist of either a tractor or rigid truck in combination with one or two cargo units. All of the combinations are commonly found on roads in Sweden and several other countries in Europe. The results from the simulations show that the aerodynamic properties differ significantly for the truck-trailer combinations. It was found that the longer vehicle combinations are much more sensitive to yaw conditions than the shorter combinations.

Presented are results from numerical investigations of buoyancy driven flow in a simplified representation of an engine bay. A main motivation for this study is the necessity for a valid correlation of results from numerical methods and procedures with physical measurements in order to evaluate the accuracy and feasibility of the available numerical tools for prediction of natural convection. This analysis is based on previously performed PIV and temperature measurements in a controlled physical setup, which reproduced thermal soak conditions in the engine compartment as they occur for a vehicle parked in a quiescent ambient after sustaining high thermal loads. Thermal soak is an important phenomenon in the engine bay primarily driven by natural convection and radiation after there had been a high power demand on the engine. With the cooling fan turned off and in quiescent environment, buoyancy driven convection and radiation are the dominating modes of heat transfer.

Today CFD is an important tool for engineers in the automotive industry who model and simulate fluid flow. For the complex field of Underhood Thermal Management, CFD has become a very important tool to engineer the cooling airflow process in the engine bay of vehicles. To model the cooling airflow process accurately in CFD, it is of utmost importance to model all components in the cooling airflow path accurately. These components are the heat exchangers, fan and engine bay blockage effect. This paper presents CFD simulations together with correlating measurements of a cooling airflow system placed in a test rig. The system contains a heavy duty truck louvered fin radiator core, fan shroud, fan ring and fan. Behind the cooling module and fan, a 1D engine silhouette is placed to mimic the blockage done by a truck engine. Furthermore, a simple hood is mounted over the module to mimic the guiding of air done by the hood shape in an engine bay.

This investigation is a continuing analysis of the cooling performance and aerodynamic properties of a rear-mounted cooling module on a semi-generic commercial vehicle, which was carried out by Larsson, Löfdahl and Wiklund. In the previous study two designs of the cooling package installation were positioned behind the rear wheelhouse and the results were compared to a front-mounted cooling module. The investigation was mainly focused on a critical cooling situation occurring at lower vehicle speeds for a local distribution vehicle. The conclusion from the study was that the cooling performance for one of the rear-mounted installation was favorable compared to the front-mounted cooling package. This was mainly due to the low vehicle speed, the high fan speed and to fewer obstacles around the cooling module resulting in a lower system restriction within the installation.

Today there are a large variety of drag-reducing devices for heavy trucks that are commonly used, for example, roof deflectors, cab side extenders and chassis fairings. These devices are often proven to be efficient, reducing the total aerodynamic resistance for the vehicle. However, the drag-reducing devices are usually identical for a specific pulling vehicle, independent of the layout of the vehicle combination. In this study, three vehicle combinations were analyzed. The total length of the vehicles varied between 10.10 m and 25.25 m. The combinations consisted of a rigid truck in combination with one or two cargo units. The size of the gap between the cargo units differed between the vehicle combinations. There were also three configurations of each vehicle combination with different combinations of roof deflector and cab side extenders, yielding a total number of nine configurations.

With the increase in fuel prices and the increasingly strict environmental legislations regarding CO₂ emissions, reduction of the total energy consumption of our society becomes more important. Passenger vehicles are partly responsible for this consumption due to their strong presence in the daily life of most people. Therefore reducing the impact of cars on the environment can assist in decreasing the overall energy consumption. Even though several fields have an impact on a passenger car's performance, this paper will focus on the aerodynamic part and more specifically, the wake behind a vehicle. By definition a car is a bluff body on which the air resistance is for the most part driven by pressure drag. This is caused by the wake these bodies create. Therefore analyzing the wake characteristics behind a vehicle is crucial if one would like to reduce drag.

This paper presents results and a Computational Fluid Dynamics (CFD) method for simulation of a detailed louvered fin for a multi-louvered compact heat-exchanger. The airflow was angled at 90°, +30° and −30° relative to the heat-exchanger to evaluate changes in static pressure drop and airflow characteristics. The investigation was based on three heat-exchangers with thicknesses of 52mm and two of 19mm. One period of a detailed louvered fin was simulated for two airflows for each heat-exchanger. The pressure drop data was thereafter compared to experimental data from a full-size heat-exchanger. From the pressure drop and the airflow characteristic results recommendations were made that those kinds of simulations could be defined as steady state, and with the kω-SST turbulence model. For the same heat-exchanger angle the airflow within the core was similar, with a turbulent characteristic behind it.