BMW’s Energy and Environment Test Centre (EVZ) was built to enhance and upgrade an already formidable collection of test capabilities within the BMW Group. The EVZ is a complex, comprising three large climatic wind tunnels, two smaller test chambers, nine soak rooms, and a complete support infrastructure. Within the multiple test facilities that make up the EVZ, nearly all environmental conditions can be simulated, which in turn reduces the dependence on on-road testing. Even more importantly, test conditions can be created accurately and with great repeatability, regardless of the time of year.
The EVZ complex is located in Munich at the BMW "FIZ," the primary technology and development center within the BMW group, and is physically situated next to the new aerodynamic complex, the AVZ. This arrangement brings together vehicle development and validation to a single location, the advantages of which are numerous: the primary one being the proximity of a multitude of engineering and technology experts to a full range of test facilities.
The initial planning of the EVZ facility began at the same time as the AVZ in 2003, but more fully evolved in 2006 when various firms were given study contracts to provide a schematic design for the facility. The design brief was to fit three climatic wind tunnels, a climatic chamber, an altitude chamber, preconditioning rooms, and various work areas into a pre-defined building envelope. To respond to the study, a joint venture was formed between MCE Stahl & Machinenbau, Imtech Deutschland GmbH & Co. KG, and Aiolos Engineering Corp. Upon completion of the study, in December 2006, this joint venture was awarded a contract to design and build the final facility.
The three wind tunnel airlines are geometrically identical, but each wind tunnel fulfills different requirements. This arrangement allowed for a savings in capital cost (e.g. cooling systems and specific test equipment such as solar simulation or rain simulation), while maintaining test flexibility.
Of the three wind tunnels, the environmental wind tunnel (UWK) offers simulation over the largest range of environmental conditions. The temperature range of this wind tunnel is from -20 to +55°C (-4 to +131°F), with humidity control up to 95% RH (non-condensing conditions) for positive temperatures. The UWK includes a full-spectrum solar simulation system, a rain simulation system, and a snow simulation system. In addition, this wind tunnel is equipped with a flat-belt drive for motorcycle testing.
The environmental range of the thermal wind tunnel (KWK) is the most restricted. In this wind tunnel, the primary tests are conducted on cooling system performance and cooling airflow in which the KWK temperature range of 20 to 45°C (68 to 113°F) is sufficient. This wind tunnel does not have a solar simulation system, nor the ability to control humidity. The thermal wind tunnel can reach the highest wind speed, 280 km/h (174 mph), compared to a maximum wind speed of 250 km/h (155 mph) in the other two wind tunnels.
The temperature range of the climatic wind tunnel (EWK) is from -10 to +45°C (+14 to +113°F) and it includes humidity control for temperatures above freezing. A full-spectrum solar simulation system is also included in this airline. In the EWK, thermal operational safety, cooling system performance, climatic control, and brake cooling tests are performed. Additionally, the EWK main fan is equipped with carbon-fiber blades, lowering fan inertia allowing for quicker wind speed response during highly dynamic tests.
The two test chambers are much smaller than the wind tunnels and, therefore, offer a greater compromise on the aerodynamic simulation. These chambers will be used for tests that are less sensitive to aerodynamic influences. However, both chambers are equipped with a full four-wheel chassis dynamometer, manufactured and installed by Maha.
The climatic chamber (KK) is the smallest chamber, with a nozzle area of just 1 m² (11-ft²). The climatic chamber will be used for cold-start tests, developmental tests of the interior heating and cooling system, and to test defrost and dehumidification cycles within the interior and at the front windscreen. The KK has a temperature range of -30°C to +30°C (-22 to +86°F), a top wind speed of 130 km/h (81 mph), and is equipped with full-spectrum solar simulation.
The altitude chamber (EK) has a 2-m² (22-ft²) nozzle, a top wind speed of 250 km/h (155 mph), a temperature range of -30 to +45°C (-22 to +113°F), a full-spectrum solar simulation system, and is equipped with humidity control for non-freezing temperatures. The primary function of this facility is altitude simulation through the control of static pressure. Altitudes from 100 m (328 ft) below sea level to 4200 m (13,780 ft) above sea level can be simulated within the EK.
Climatic wind tunnels have always been smaller than wind tunnels designed for aerodynamic development; it is not feasible to build such large climatic wind tunnels. As a result, the aerodynamic simulation within a climatic wind tunnel is compromised—i.e. boundary influences will be more prevalent. But, as more of the tests that have traditionally been performed on test tracks are moved into the climatic wind tunnel, the quality of the aerodynamic simulation becomes more and more important. To meet the needs of BMW today and in the future, the climatic wind tunnels were built to aerodynamic specifications that are comparative to (and in some cases, exceed) many purely aerodynamic facilities in use today, exclusive of nozzle size.
After completion of the aerodynamic commissioning and before actual vehicle testing, verification and correlation studies were carried out by BMW. These studies involved instrumenting several vehicles with temperature and flow measurement equipment for comparison studies to other test facilities, including the new AVZ, and to on-track measurements.
In general, the test fidelity of the EVZ wind tunnels could be verified through flow comparisons to the AVZ and temperature comparisons to on-road tests. Small temperature deviations could usually be attributed to external sources or known limitations, such as slightly differing starting temperatures. However, slight temperature deviations could be consistently seen at the rear underbody of many of the test vehicles, indicating boundary layer influences.
The validation tests were carried out in each of the EVZ wind tunnels. Several different vehicles were instrumented with thermocouples in various areas, including the engine, gearbox, cooling system, carriage, exhaust system, fuel tank, and fire protection. The general procedure required at least two independent measurements at the BMW test center in Miramas, France, and two measurements in at least one of the EVZ wind tunnels. The test matrix used speeds between 35 and 250 km/h (22 and 155 mph) and included matching environmental loads, such as uphill and downhill grades. In all cases, the operating modes (gear selection, engine speed, air-conditioning settings, temperature, and humidity) were all matched in the EVZ.
In repeatability tests within the EVZ for air-conditioning and cooling system tests, it has been found that 95% of the measured temperatures are within a repeatability of ±1°C (1.8°F).
This article is based on SAE International technical paper 2011-01-0167 by Trevor Bender, Aiolos Engineering Corp.; and Peter Hoff and Roland Kleemann, BMW AG.