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P. Liu
6.6 Transonic Wind Tunnel
1. General
The Mach number of the transonic wind tunnel is about 0.8−1.4. The
lower limit is 0.8 because the Mach number of congestion (blockage) in
the tunnel wall (non-vented wall) of the test section is generally around
0.8. To make the Mach number more than 0.8, methods should be taken
to solve the congestion problem. The Mach number is around 1.4, and the
general supersonic nozzle and solid wall test section can be used, belonging
to the category of supersonic wind tunnel. There are three differences
between supersonic wind tunnel and transonic wind tunnel. First, the
wall of the supersonic wind tunnel test section is the solid wall, the wall
of the transonic wind tunnel test section is the breathable wall (hole or
grooved wall). The four walls are the ventilation wall or the upper and
lower two walls are the ventilation wall in transonic wind tunnel. Outside
of the ventilation wall is a cavity called a chamber. The ventilation wall
includes a perforated wall or slotted wall or a perforated and slotted wall.
The ratio of the ventilation area of the wall to the total area of the wall
is called the open-close ratio. Under certain conditions, part of the air in
the test section flows into the compartment through the ventilation wall.
Second, before the supersonic wind tunnel test section, there is a supersonic nozzle that first shrinks and then expands. During the wind tunnel
operation, the Mach number at the nozzle throat is 1, and the Mach
number at the nozzle outlet is greater than 1. The transonic wind tunnel
is different. In front of the test section, the pipe is simply contracted,
and the maximum Mach number at the outlet of the pipe is 1. Third,
to get different Mach numbers in the supersonic wind tunnel, the area
ratio of the nozzle should be changed. In a transonic wind tunnel, by
changing the ratio of static pressure at the entrance of the test section to
the static pressure at the chamber, different Mach numbers in the transonic range can be obtained by simply contracting the same pipe (i.e., the
area ratio remains unchanged). In the development history of a transonic
wind tunnel, the most important technical breakthrough is the adoption
of a ventilation wall, whose main functions are as follows: (1) to prevent
airflow congestion in the test section. In the real wall test section, when the
incoming flow approaches the sound velocity, the phenomenon of congestion will occur. The model is installed in the test section and a minimum
section is formed between the model and the cave wall. Even if there is no
model in the test section, the section with the minimum effective crosssectional area will be formed in the test section due to the existence of
P. Liu
6.6 Transonic Wind Tunnel
1. General
The Mach number of the transonic wind tunnel is about 0.8−1.4. The
lower limit is 0.8 because the Mach number of congestion (blockage) in
the tunnel wall (non-vented wall) of the test section is generally around
0.8. To make the Mach number more than 0.8, methods should be taken
to solve the congestion problem. The Mach number is around 1.4, and the
general supersonic nozzle and solid wall test section can be used, belonging
to the category of supersonic wind tunnel. There are three differences
between supersonic wind tunnel and transonic wind tunnel. First, the
wall of the supersonic wind tunnel test section is the solid wall, the wall
of the transonic wind tunnel test section is the breathable wall (hole or
grooved wall). The four walls are the ventilation wall or the upper and
lower two walls are the ventilation wall in transonic wind tunnel. Outside
of the ventilation wall is a cavity called a chamber. The ventilation wall
includes a perforated wall or slotted wall or a perforated and slotted wall.
The ratio of the ventilation area of the wall to the total area of the wall
is called the open-close ratio. Under certain conditions, part of the air in
the test section flows into the compartment through the ventilation wall.
Second, before the supersonic wind tunnel test section, there is a supersonic nozzle that first shrinks and then expands. During the wind tunnel
operation, the Mach number at the nozzle throat is 1, and the Mach
number at the nozzle outlet is greater than 1. The transonic wind tunnel
is different. In front of the test section, the pipe is simply contracted,
and the maximum Mach number at the outlet of the pipe is 1. Third,
to get different Mach numbers in the supersonic wind tunnel, the area
ratio of the nozzle should be changed. In a transonic wind tunnel, by
changing the ratio of static pressure at the entrance of the test section to
the static pressure at the chamber, different Mach numbers in the transonic range can be obtained by simply contracting the same pipe (i.e., the
area ratio remains unchanged). In the development history of a transonic
wind tunnel, the most important technical breakthrough is the adoption
of a ventilation wall, whose main functions are as follows: (1) to prevent
airflow congestion in the test section. In the real wall test section, when the
incoming flow approaches the sound velocity, the phenomenon of congestion will occur. The model is installed in the test section and a minimum
section is formed between the model and the cave wall. Even if there is no
model in the test section, the section with the minimum effective crosssectional area will be formed in the test section due to the existence of