PowerCOOL Examples
Case Study: Land Rover LR3
Measuring and analyzing cooling airflow has always been difficult, especially as driving conditions change or if underhood geometry is modified. Below you will find information regarding a simulation performed with PowerFLOW and PowerCOOL to calculate the Land Rover LR3 underhood airflow structures and cooling performance for three simulated driving conditions: idle, high velocity and maximum velocity.
Detailed geometry details are shown below. No simplifications were made to the original CAD data and even minute geometric details were considered. This is critical if we want to accurately reproduce the real world cooling airflow. Using CAD geometry without simplifications also considerably reduces case preparation time since any alterations are time consuming.
Measured thermal characteristics of heat exchangers are a very important input to cooling airflow simulations. Heat exchangers like radiators, charge-air-coolers and condensers are modeled as porous media. Heat transfer between the air and heat exchangers is governed by the heat transfer coefficient which is a measured parameter. Heat transfer coefficients are measured as a function of the air and coolant mass flow rates. The measured values can be interpolated using the “sandwich formula” which relates the heat transfer coefficient to the coolant and air mass flow rates.
Land Rover LR3: heat transfer coefficients at different coolant mass flow rates: a.) the radiator, b.) the charge-air-cooler (black dots – data, red lines – interpolations).
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The details of the Land Rover LR3 cooling package are shown below. The condenser is placed in front of the radiator. Both condenser and radiator are placed on top of the charge-air-cooler and are mostly unaffected by the hot air at its exit.
Configuration of the underhood geometry for Land Rover LR3.
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The experimentally measured operating parameters for the radiator and charge-air-cooler at three different driving conditions are shown in the table below. Radiator internal mass flow rate and heat rejection are provided. PowerCOOL is asked to calculate the inlet coolant temperature to the radiator (rather than the heat rejection) .
Land Rover LR3 case parameters
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Operating Condition
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idle
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Low Velocity
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Max. Velocity
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Air Velocity
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0 km/h
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95km/h
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179 km/h
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Ambient Air Temp.
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46.8°C
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31.3°C
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42.0°C
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Size[MFe (V/S)]
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8.2/7.7
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8.2/7/7
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8.2/7/7
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Charge Air Cooler
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0.015 kg/s
100°C
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0.097 kg/s
195°C
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0.138 kg/s
200°C
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Radiator
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0.44 kg/s
11.6 kW
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1.77 kg/s
65.2 kW
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2.44 kg/s
83.8 kW
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Condenser
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8.0 kW
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12.0kW
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12.0KW
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Fan
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1003.5 RPM
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2440 RPM
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2143.5 RPM
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The calculated air temperature fields just behind the radiator are shown in the figures below. The first figure shows the temperature in the idle case. The high temperature region around the top radiator edge and corners is due to the flow recirculation. At high velocity, a high temperature region can be observed developing from the right edge of the radiator as seen in the following figures. This is because the coolant entry location is at the right side of the radiator. Higher temperature is also due to significantly higher heat rejection than in the idle case (see previous table).
Air temperature distribution on the plane behind the radiator for the Land Rover LR3 cases: a.) idle, b.) 95GVW, and c.) Vmax.
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One of the most important and interesting effects in cooling airflows is the recirculation at low velocity and idle conditions. The time evolution of the temperature field for the LR3 idle case is shown in the next figure. Air temperature starts to rise just behind the heat exchangers (0.09s and 0.15s). Part of the air coming out of the heat exchangers returns upstream slowly carrying hot air along its path. As a result, hot air moves in both downstream and upstream directions (0.30s to 1.05s). The portion of the hot air flowing upstream re-enters the heat exchangers causing a complicated feedback between the hot air entering and exiting the heat exchangers (1.34s to 1.47s). The entire process is slow due to the low velocity of the recirculating air. The air temperature at the inlet of the radiator is a result of a very complex interaction between the cooling airflow, the heat exchangers, and the recirculating hot air. In the present case, there are no experimental air velocity and temperature measurements available that could be used for the comparison with the simulation predictions. However, the entire simulation was validated indirectly by comparing the predicted and experimentally measured radiator inlet coolant temperatures.
Evolution of the temperature field as a function of time for idle case , which is dominated by recirculation effects.
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The main parameter of interest is actually the coolant temperature at the inlet into the radiator (top tank temperature). The difference between the measured values and the predictions is shown in the table below. The largest difference can be observed for the maximum velocity case, while the least difference is in the 95GVW case.
Difference between the measured and predicted top tank temperatures for the radiator.
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Car
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Land Rover LR3
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Case
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Idle
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95GVW
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Vmax
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Difference
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2.1°C
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1.0°C
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4.3°C
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Available Publications:
1. A. Alajbegovic, R. Sengupta, W. Jensen, “Cooling Airflow Simulations for Passenger Cars Using Detailed Underhood Geometry,” SAE 2006-01-3478.
2. J. Amodeo, A. Alajbegovic, W. Jansen, “Thermal Management Simulation for Passenger Cars – Towards Total Vehicle Analysis ,” 6th MIRA International Conference, 2006.
3. A. Alajbegovic, B. Xu, A. Konstantinov, J. Amodeo, W. Jansen, “Simulation of Cooling Airflow Under Different Driving Conditions,” SAE 2007-01-0766.
