6 Wind and Water Tunnel Equipment
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mostly closed-section. If the blow-down low-speed wind tunnel is openjet, an airtight chamber must be placed outside the open test section.
Otherwise, since the fan is located behind the test section, air will flow
directly into the test section, resulting in transverse flow in the test section.
The loop wind tunnel is divided into a circular loop and an ordinary
single loop. A loop wind tunnel is usually a pressure wind tunnel. This
wind tunnel requires the total pressure of the gas in the wind tunnel to be
0.125−25 times the atmospheric pressure before the wind tunnel works.
The Reynolds number can be increased when the pressure is high, and
the Mach number can be increased when the pressure is low. The cave of
this kind of wind tunnel can withstand the pressure difference between
inside and outside. Common single-loop wind tunnels, including open
and closed test sections, are familiar. Most low-speed wind tunnels in the
world are horizontal, that is, the center line of the wind tunnel is on
the horizontal surface. If the center line of the test section of the wind
tunnel is in the vertical direction, the wind tunnel is vertical. Aircraft tailspin test, manned spacecraft re-entry module-parachute system dynamic
stability test, etc. need to be carried out in vertical wind tunnel.
In the field of aeronautics and astronautics, low-speed wind tunnels are
classified according to their purposes, mainly as follows:
(1) Two-dimensional wind tunnel (binary wind tunnel). The cross section
of the test section of this wind tunnel is rectangular, and the ratio of
the length on both sides is 2.5−4. The two-dimensional wind tunnel
is mainly used to study the aerodynamic characteristics of airfoils.
(2) Three-dimensional wind tunnel (ternary wind tunnel), namely the
general wind tunnel. In this kind of wind tunnel, a full-machine
model or semi-model test can be carried out, mainly used to measure
the aerodynamic force, pressure distribution, and velocity field acting
on the model, which is the most widely applied wind tunnel.
(3) Low-turbulence wind tunnel. The turbulence of the airflow in the test
section of the wind tunnel is very low and can be adjusted. Generally, the turbulence in the cleared atmosphere is about 0.01−0.03%.
The turbulence in a normal medium-large low-speed reflux wind
tunnel can reach 0.1−0.5% or more, while the turbulence in a lowturbulence wind tunnel should be less than 0.05%. Low-turbulence
wind tunnels are mainly used to study the flow phenomena that are
greatly affected by turbulence, such as boundary layer transition, separation flow, vortex rupture, and other experimental studies. Such wind
tunnels can be two-dimensional or three-dimensional, characterized
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mostly closed-section. If the blow-down low-speed wind tunnel is openjet, an airtight chamber must be placed outside the open test section.
Otherwise, since the fan is located behind the test section, air will flow
directly into the test section, resulting in transverse flow in the test section.
The loop wind tunnel is divided into a circular loop and an ordinary
single loop. A loop wind tunnel is usually a pressure wind tunnel. This
wind tunnel requires the total pressure of the gas in the wind tunnel to be
0.125−25 times the atmospheric pressure before the wind tunnel works.
The Reynolds number can be increased when the pressure is high, and
the Mach number can be increased when the pressure is low. The cave of
this kind of wind tunnel can withstand the pressure difference between
inside and outside. Common single-loop wind tunnels, including open
and closed test sections, are familiar. Most low-speed wind tunnels in the
world are horizontal, that is, the center line of the wind tunnel is on
the horizontal surface. If the center line of the test section of the wind
tunnel is in the vertical direction, the wind tunnel is vertical. Aircraft tailspin test, manned spacecraft re-entry module-parachute system dynamic
stability test, etc. need to be carried out in vertical wind tunnel.
In the field of aeronautics and astronautics, low-speed wind tunnels are
classified according to their purposes, mainly as follows:
(1) Two-dimensional wind tunnel (binary wind tunnel). The cross section
of the test section of this wind tunnel is rectangular, and the ratio of
the length on both sides is 2.5−4. The two-dimensional wind tunnel
is mainly used to study the aerodynamic characteristics of airfoils.
(2) Three-dimensional wind tunnel (ternary wind tunnel), namely the
general wind tunnel. In this kind of wind tunnel, a full-machine
model or semi-model test can be carried out, mainly used to measure
the aerodynamic force, pressure distribution, and velocity field acting
on the model, which is the most widely applied wind tunnel.
(3) Low-turbulence wind tunnel. The turbulence of the airflow in the test
section of the wind tunnel is very low and can be adjusted. Generally, the turbulence in the cleared atmosphere is about 0.01−0.03%.
The turbulence in a normal medium-large low-speed reflux wind
tunnel can reach 0.1−0.5% or more, while the turbulence in a lowturbulence wind tunnel should be less than 0.05%. Low-turbulence
wind tunnels are mainly used to study the flow phenomena that are
greatly affected by turbulence, such as boundary layer transition, separation flow, vortex rupture, and other experimental studies. Such wind
tunnels can be two-dimensional or three-dimensional, characterized