112
4 Transonic Wind Tunnels
Fig. 4.19 Operating domains of the ETW wind tunnel in Cologne (© ETW)
size of the working section and the environmental conditions helps in attaining similar conditions achieved during cruise conditions which makes this tunnel the most
strategic for the aerospace industry.
The operating ranges with respect to each Mach number can be summarised
into an overall ETW performance envelope expressed as Reynolds number against
Mach number in Fig. 4.19. Pure Reynolds number or aerodynamic loads variations
at constant Mach number can be achieved by adjusting the total pressure and temperature accordingly. Testing at ambient temperature allows data comparison with
conventional low- or high-speed tunnels.
Up to the Mach number of 0.7 (Mach number 1 if the second throat is fully open),
the flow speed is controlled by the fan speed. From the Mach number of 0.7–1,
the second throat is used to control the Mach number of the flow in the test section.
Beyond the Mach number of 1, the supersonic nozzle is the main element controlling
the flow speed. With full-span aircraft models a Reynolds number of about 50 million
can be reached, and when a larger ceiling mounted half (semi-span) model is used
then Reynolds numbers of up to 85 million can be achieved. These Reynolds numbers
are based on the mean aerodynamic cord of the respective wing. The upper Reynolds
number limit is obtained at the minimum temperature and at the first reach of either
the maximum pressure or the maximum drive power.
To ensure the operation in the cold environment, the ETW team has developed a
transportable model interchange system based on a cart containing the model and its
support, the top wall of the test chamber, the access hatch and the instrumentation
box, the full assembly being moved by a carrier. The models are prepared in two halls:
one with ambient air and a second “dry” hall filled with dry air at room temperature
whose dew point is kept low enough to prevent icing and ice formation on the cold
model. The two halls are separated by a transfer air locked, where the model and its
4 Transonic Wind Tunnels
Fig. 4.19 Operating domains of the ETW wind tunnel in Cologne (© ETW)
size of the working section and the environmental conditions helps in attaining similar conditions achieved during cruise conditions which makes this tunnel the most
strategic for the aerospace industry.
The operating ranges with respect to each Mach number can be summarised
into an overall ETW performance envelope expressed as Reynolds number against
Mach number in Fig. 4.19. Pure Reynolds number or aerodynamic loads variations
at constant Mach number can be achieved by adjusting the total pressure and temperature accordingly. Testing at ambient temperature allows data comparison with
conventional low- or high-speed tunnels.
Up to the Mach number of 0.7 (Mach number 1 if the second throat is fully open),
the flow speed is controlled by the fan speed. From the Mach number of 0.7–1,
the second throat is used to control the Mach number of the flow in the test section.
Beyond the Mach number of 1, the supersonic nozzle is the main element controlling
the flow speed. With full-span aircraft models a Reynolds number of about 50 million
can be reached, and when a larger ceiling mounted half (semi-span) model is used
then Reynolds numbers of up to 85 million can be achieved. These Reynolds numbers
are based on the mean aerodynamic cord of the respective wing. The upper Reynolds
number limit is obtained at the minimum temperature and at the first reach of either
the maximum pressure or the maximum drive power.
To ensure the operation in the cold environment, the ETW team has developed a
transportable model interchange system based on a cart containing the model and its
support, the top wall of the test chamber, the access hatch and the instrumentation
box, the full assembly being moved by a carrier. The models are prepared in two halls:
one with ambient air and a second “dry” hall filled with dry air at room temperature
whose dew point is kept low enough to prevent icing and ice formation on the cold
model. The two halls are separated by a transfer air locked, where the model and its