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air duct

The fan, with a diameter of 3.55 m and a maximum power of 1300 kW, propels the air via the long diffuser towards the heat exchanger(face area 36 m²).

fan	air duct of the climatic wind tunnel

The tempered air flows via two corners, each equipped with guide vanes, into the settling chamber - also with a cross-section of 36 m². From there it is accelerated progressively in the nozzle, up to a maximum wind speed of 265 km/h. On entering the working section, it flows over the test vehicle and is withdrawn via the collector. The guide vane array of the lower corner (following the test section) is divided into two equal halves. By moving aside, they give test vehicles access to the test section

nozzle

In addition to the maximum wind speed the air jet section, the size and shape, are the core indicatore of the climatic wind tunnel. It is responsible for

• the dimensions of the whole wind tunnel and thus much of the capital cost;
• the power of the fan drive and of the cooling plant- and with it most of the operating costs.

Consequently the nozzle exit area should be large enough to create a flow field over the test vehicle that is as realistic as necessary, but no larger. The relation between the frontal area of the test vehicle, A_vehicle, to the exit area of the nozzle, A_nozzle, is known as the ‘blockage ratio‘ j = A_vehicle / A_nozzle. Many comparative measurements have shown that a climatic wind tunnel can have a blockage ratio much larger than that of an aerodynamic wind tunnel. For climatic wind tunnels, values of 0.3 to 0.4 have proven sufficient.

In such cases the flow field over the front part of test vehicles and the airflow in the vehicle interiors agree sufficiently well with those measured on the road, or in a big wind tunnel. For the Modine wind tunnel, the nozzle exit area, A_nozzle, was fixed at 4.7 m² (2.3 x 2.05 m). For a passenger car with a frontal area, A_vehicle, of 2.0 m² this gives a blockage ratio of j = 0.42, which is just within the range given above.

For big trucks and buses a nozzle exit area of 12 m² is provided. To enable these two very different nozzle areas to be provided in one wind tunnel, the Modine climatic wind tunnel has a ‘tandem nozzle‘. As shown in Fig., this consists of two nozzles arranged one after the other.

car nozzle (tandem nozzle)	truck & bus nozzle

When a passenger car is in the test section, both nozzles are used in series. With a nozzle exit area of 5.3 m², a maximum wind speed of 265 km/h can be reached. If a truck or bus is being tested, the second nozzle is removed sideways from the wind tunnel, and the airflow is guided laterally by two inward-folding flat walls. With just the first nozzle, with its exit area of 12 m², a wind-speed of 130 km/h can be reached. This is quite enough for testing trucks and buses.

The big advantage of the tandem-nozzle is that the wind tunnel flow field matches the different vehicles in both height and width. The change-over takes less than 30 minutes.