Simulation of thermal tests in the climatic wind tunnel CD7 at Scania Master thesis project in fluid mechanics
Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
The Swedish truck and bus manufacturer Scania has a number of test facilities to support the R&D department and for verification of vehicle properties. The latest addition is the climatic wind tunnel Chassis Dynamometer 7 (CD7) which can fit trucks and buses for full scale testing and maintain temperatures in the range from -35 to 50 degree Celsius in the flow circuit, furthermore it can generate both rain and snow conditions. This means that vehicles can be tested in a controlled and repeatable manner at many critical driving conditions. However, since CD7 is a new facility there is a need to tune and interpret the results generated in the tunnel and translate them to true, on road conditions. In this project the airflow and temperature distribution in the climatic wind tunnel were studied by means of the CFD solver PowerFLOW based on the Lattice Boltzmann method. As a first step the wind tunnel was simulated empty to check the case set up and to understand the basic flow features in the empty tunnel. In the second step a Scania truck was added to the wind tunnel set up, a truck that also exists as a physical test vehicle at Scania R&D. Thirdly, the same vehicle model was simulated in road like conditions to give a reference for comparison. Lastly, a measurement campaign was performed in the climatic wind tunnel in order to get data for comparison and validation of the simulation results. Simulation results show that CD7 displays an overestimate of wind tunnel airspeed. To match heat exchanger mass flow and recirculation temperatures at 30 km/h it is shown that CD7 should indicate closer to 35 km/h. At this low speed range 5 km/h has a strong effect on recirculation of hot air into the cooling package which translates to 1 C increase of air temperature into the charge-air cooler. It also corresponds to an increase of 2 C of the cooling capacity of the vehicle at 30 km/h. Also the temperature in the front air intake system increases by 3 C which is also a significant change that could affect the tuning of the engine. One degree Celsius is within the measurement accuracy of a thermal test at Scania. The simulations at 85 km/h give a corresponding correction of the tunnel velocity around 10 km/h, which means that it is consistently about 10 % off. The experimental results show conformity with the simulations and also support the claim that CD7 indicates an overestimate of the actual airspeed.
Place, publisher, year, edition, pages
2016. , 68 p.
Engineering and Technology
IdentifiersURN: urn:nbn:se:kth:diva-195726OAI: oai:DiVA.org:kth-195726DiVA: diva2:1045337
Alfredsson, Henrik, Professor