6 Wind and Water Tunnel Equipment
403
of the tunnel, longitudinal ribs and tunnel supports are arranged in many
places. Rubber pads are added between the flanges at the joints of each
section of the wind tunnel to eliminate and alleviate the vibration caused
by gas flow and fan section. In order to adapt to the deformation caused by
temperature, the two ends of the tunnel can be expanded freely. In order to
reduce the vibration and noise, the foundation of fan section, test section,
and cave section is poured separately. At the same time, vibration isolation
material is used at the bottom of the fan section to reduce the sound and
vibration transmission through the foundation. The motor is arranged in
the fan fairing to avoid the long shaft connection passing through the
corner deflector and affecting the airflow quality and uniformity in the
fan room.
In addition to the requirements of flow field quality, the aeroacoustic
wind tunnel also has acoustic field quality, including low background
noise and non-reflection free field conditions, as well as sufficient space
size to satisfy far-field acoustic measurements. In D5 wind tunnel, the
background noise level of the wind tunnel is reduced by laying acoustic
liner material on the tunnel wall, and no reflection condition and farfield sound measurement are achieved by building an anechoic chamber
outside the test section. The background noise in the wind tunnel test
section can usually be divided into two parts: one is the rotating noise
and eddy noise generated by the axial flow fan in the wind tunnel during
the operation process. The other is the regenerative noise generated by
the airflow in the wind tunnel during the flow process as the secondary
sound source. The background noise includes both broadband noise and
discrete noise. Therefore, necessary noise reduction methods should be
taken to acoustically treat the wind tunnel loop and achieve the goal of
reducing background noise. The D5 wind tunnel adopts a noise reduction scheme with the combination of a single-channel resistive silencer
and micro-perforated plate silencer to reduce the background noise (as
shown in Fig. 6.20). A micro-perforated plate silencer is used in the fan
power section to eliminate the low- and medium-frequency band noise
generated by the fan, and a single-channel resistive silencer is used in the
tunnel wall to eliminate the medium- and high-frequency band noise.
The background noise of the D5 wind tunnel is measured in the
anechoic chamber during operation in the open test section. The measured
position is located outside the airflow field, 1.5 times the wind tunnel
diameter (1.5 m) from the central axis of the wind tunnel and 1 m from
the downstream of the nozzle, flush with the central axis of the wind
tunnel. In the test, the background noise value at the speed of 20−80 m/s
403
of the tunnel, longitudinal ribs and tunnel supports are arranged in many
places. Rubber pads are added between the flanges at the joints of each
section of the wind tunnel to eliminate and alleviate the vibration caused
by gas flow and fan section. In order to adapt to the deformation caused by
temperature, the two ends of the tunnel can be expanded freely. In order to
reduce the vibration and noise, the foundation of fan section, test section,
and cave section is poured separately. At the same time, vibration isolation
material is used at the bottom of the fan section to reduce the sound and
vibration transmission through the foundation. The motor is arranged in
the fan fairing to avoid the long shaft connection passing through the
corner deflector and affecting the airflow quality and uniformity in the
fan room.
In addition to the requirements of flow field quality, the aeroacoustic
wind tunnel also has acoustic field quality, including low background
noise and non-reflection free field conditions, as well as sufficient space
size to satisfy far-field acoustic measurements. In D5 wind tunnel, the
background noise level of the wind tunnel is reduced by laying acoustic
liner material on the tunnel wall, and no reflection condition and farfield sound measurement are achieved by building an anechoic chamber
outside the test section. The background noise in the wind tunnel test
section can usually be divided into two parts: one is the rotating noise
and eddy noise generated by the axial flow fan in the wind tunnel during
the operation process. The other is the regenerative noise generated by
the airflow in the wind tunnel during the flow process as the secondary
sound source. The background noise includes both broadband noise and
discrete noise. Therefore, necessary noise reduction methods should be
taken to acoustically treat the wind tunnel loop and achieve the goal of
reducing background noise. The D5 wind tunnel adopts a noise reduction scheme with the combination of a single-channel resistive silencer
and micro-perforated plate silencer to reduce the background noise (as
shown in Fig. 6.20). A micro-perforated plate silencer is used in the fan
power section to eliminate the low- and medium-frequency band noise
generated by the fan, and a single-channel resistive silencer is used in the
tunnel wall to eliminate the medium- and high-frequency band noise.
The background noise of the D5 wind tunnel is measured in the
anechoic chamber during operation in the open test section. The measured
position is located outside the airflow field, 1.5 times the wind tunnel
diameter (1.5 m) from the central axis of the wind tunnel and 1 m from
the downstream of the nozzle, flush with the central axis of the wind
tunnel. In the test, the background noise value at the speed of 20−80 m/s