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P. Liu
(4) The stable section is a pipe section of sufficient length with a constant
cross section. It is characterized by a large enough cross-sectional
area, low airflow speed, and rectifier device in the stable section. The
function of the stability section is to stabilize the turbulent and nonuniform airflow from the upstream, so that the vortex attenuation,
velocity size, and direction distribution are more uniform.
(5) The rectifier device refers to the honeycomb device and the rectifier net (damping net). The honeycomb device is composed of many
square or hexagonal cells, such as honeycomb. The rectifier net is a
small mesh wire diameter of the small metal net, can have a layer
or several layers. The honeycomb device can guide the airflow and
reduce the scale of the large eddy and the transverse turbulence of
the airflow. The large-scale vortexes can be divided into smaller scale
vortexes by the rectifier net, while the small-scale vortexes can be
attenuated within a sufficient length of the stable section behind the
rectifier network, so that the turbulence of the airflow, especially the
axial turbulence, can be significantly reduced. In addition, the energy
loss of the airflow through the rectifier device is related to the size
of the incoming flow velocity. If the distribution of the incoming
flow velocity is not uniform in the cross section, the airflow with
high velocity loses more while the airflow with low velocity loses less.
Therefore, the rectifier device can make the distribution of the airflow
velocity become even. The turbulence, flow direction, and velocity
distribution uniformity of the airflow can be improved obviously by
the well-designed stable section, honeycomb, and rectifier net system.
(6) Contraction section: In a low-speed wind tunnel, the contraction
section is located between the stable section and the test section,
which is a smooth transition curved pipe, with the cross-sectional
area gradually decreasing along the flow direction. If the contract
period of the cross-sectional area of the entrance section is A1, crosssectional area of exit is A 0 , η = A 1
A 0 is shrinkage ratio. The
function of the contraction section is to make the airflow from the
stable section accelerate uniformly and improve the flow field quality
(airflow uniformity, turbulivity, etc.) of the test section. The design
of the contraction section should meet the following requirements:
when the air flows through the contraction section, the flow rate
increases monotonously to avoid the separation of the airflow on the
P. Liu
(4) The stable section is a pipe section of sufficient length with a constant
cross section. It is characterized by a large enough cross-sectional
area, low airflow speed, and rectifier device in the stable section. The
function of the stability section is to stabilize the turbulent and nonuniform airflow from the upstream, so that the vortex attenuation,
velocity size, and direction distribution are more uniform.
(5) The rectifier device refers to the honeycomb device and the rectifier net (damping net). The honeycomb device is composed of many
square or hexagonal cells, such as honeycomb. The rectifier net is a
small mesh wire diameter of the small metal net, can have a layer
or several layers. The honeycomb device can guide the airflow and
reduce the scale of the large eddy and the transverse turbulence of
the airflow. The large-scale vortexes can be divided into smaller scale
vortexes by the rectifier net, while the small-scale vortexes can be
attenuated within a sufficient length of the stable section behind the
rectifier network, so that the turbulence of the airflow, especially the
axial turbulence, can be significantly reduced. In addition, the energy
loss of the airflow through the rectifier device is related to the size
of the incoming flow velocity. If the distribution of the incoming
flow velocity is not uniform in the cross section, the airflow with
high velocity loses more while the airflow with low velocity loses less.
Therefore, the rectifier device can make the distribution of the airflow
velocity become even. The turbulence, flow direction, and velocity
distribution uniformity of the airflow can be improved obviously by
the well-designed stable section, honeycomb, and rectifier net system.
(6) Contraction section: In a low-speed wind tunnel, the contraction
section is located between the stable section and the test section,
which is a smooth transition curved pipe, with the cross-sectional
area gradually decreasing along the flow direction. If the contract
period of the cross-sectional area of the entrance section is A1, crosssectional area of exit is A 0 , η = A 1
A 0 is shrinkage ratio. The
function of the contraction section is to make the airflow from the
stable section accelerate uniformly and improve the flow field quality
(airflow uniformity, turbulivity, etc.) of the test section. The design
of the contraction section should meet the following requirements:
when the air flows through the contraction section, the flow rate
increases monotonously to avoid the separation of the airflow on the