The main use of climatic wind tunnels today is for thermal studies of vehicles, in particular for studying the cooling systems of the engine, transmission and brakes. In addition, the tunnels are used for testing vehicle air conditioning systems. They are also used to eliminate the need for carrying out measurement on roads and tracks as far as possible, therefore saving time and work.

       However, wind tunnel measurements must also be of the highest quality before they can be used in order to reproduce the results of road driving. Numerous test systems and vehicle parameters play a role here and must be taken into consideration Vehicle manufacturers are constantly presenting greater demands in their testing specifications, as seen for example in the dynamic simulation of driving cycles and route profiles. The required high speeds and repid accelerations require a high level of performance and accuracy in the testing equipment and highly developed testing techniques. Differences between road and wind tunnel testing can typically be avoided with a state-of-the-art test facility and refined methods.

       Modine has operated climatic wind tunnels t central locations in the USA, Asia and Europe since 1941. The climatic center in Filderstadt/Bonlanden, Germeny, went into operation in 2004. This state-of-the-art facility comprises a climatic wind tunnel and a climate chamber.

       The test cells are used primarily for internal development and for validation, but can also be made available to external customers for their own testing purposes. Figure 1 shows the view through the nozzle of the climatic wind tunnel, while Figure 2 illustrates the climatic chamber.

       Climatic wind tunnels have primarily been used for measurement under steady-state operating conditions; that is, at constant velocities and whit constant engine loads. However, changes in testing requirements have made it increasingly necessary to show driving cycles as well.

       These changes have taken the form of laws requiring specific velocity cycles over a period of time, as in the New European Drive Cycle (NEDC). In addition to these velocity cycles, which tend on the whole to be moderate, certain types of tests also call for high accelerations or extreme reductions of speed, as in the case of brake tests. In addition, vehicle manufacturers want to see typical profiles of behavior on the road in order to evaluate their vehicles. This may involve mountain driving (over the Grofsglockner Mountain in the Swiss Alps, the Towns Pass, through the Black Forest in Germany, the Ardennes Forest in Belgium) or even test drives on speed tracks such as Germany’s Nurburgring.
More and more, these tests are also being demanded in the wind tunnel. This requires a preliminary reference drive over actual roads for the purpose of recording not only the vehicle’s data (driving speeds, engine rpm, gears, etc.), but also in order to record via GPS a profile of the road. Data on elevations, recorded all along the distance traveled, also make it possible to correctly simulate the effect of gradients in the wind tunnel. The vehicle’s driver assistance system and a monitor in the vehicle give the driver all the information he needs to reproduce the road conditions in the form of target speeds, real speeds, gears used, and gradients.

       Figure 3 shows an animated roadway view as seen from the driver’s seat. The driver can use this to adjust for approaching gradient changes. It is possible to reproduce the reference measurement results-for example in hot desert conditions-and roadway-conditioned drives with different vehicles.

       Figure 4 helps to shows the progression of roll speeds of the front and rear rollers (dynamometers) under rapid acceleration and braking. The test vehicle in this case was a standard production sports car with rear-wheel drive. At first the vehicle was accelerated at full power in sixth gear, then braked abruptly, then accelerated at full power in fifth gear and so on. At the end, the vehicle was again set in motion in first gear. The front roller was also controlled at the test cell control panel. The acceleration capability of the dynamometers and the excellent synchronization between the front and rear rollers are clearly noticeable. Only between shifting gears were there brief deviations; these tended to be recognizable only with very small axis values.

      Experience has shown that the excellent roller synchronization makes it unnecessary to turn off electronic systems for driving stabilization (ESP). This is also true of four –wheel drive vehicles. The rollers are capable of withstanding very high tension and braking forces, so that acceleration and braking tests (for example retarding operations) can be carried out even with heavy truck applications at up to 40kN for brief periods. Tire slip is avoided by a special coating of the roller surface.

      Wind speed has to be simulated simultaneously with the dynamometer speed. However, acceleration of the fan may be somewhat slower. If the fan just follows the dynamometer, a time lag of a few seconds may occur. In order to compensate for that, the fan can be started earlier and controlled independently. Wind speed synchronization within one or two seconds can be achieved using this method.

      Plenum temperature can be kept close to the setpoint, the deviation typically being within 1K. This also applies to the humidity.

      Modine has increased the maximum speed capacity of the dynamometers in the wind tunnel to 280km/h (173mph).

      With a new nozzle insert, wind speeds up to 268km/h (166mph) can be reached. Nozzle size is 4.8m2. Velocity distribution over the whole speed range is excellent: the standard deviation with the empty plenum at 100km/h (62mph) is 0.2%.