432
P. Liu
high temperature up to 6000 K or even higher. Since the temperature is
higher than 600 K, the temperature rises further, gas molecules can appear
and so also the phenomena such as vibration, dissociation, and ionization,
which changes the nature of the air. The specific heat ratio no longer remains
constant but changes as the temperature changes. The perfect gas equation of
state is no longer applicable. Isentropic relationship fails. Enthalpy no longer
linearly increases with the temperature and is under the influence of the pressure at the same time. This real gas effect obviously has a considerable impact
on the aerodynamic characteristics of the shuttle. It is very difficult to fully
simulate the shuttle’s return to the various stages of flight in an experimental
facility. In the hypersonic continuous flow region, the main parameters for
simulation in the space shuttle aerodynamic test are Mach number, Reynolds
number, and enthalpy. Hypersonic wind tunnel can simulate high Mach
number (5−14) but cannot simulate high enthalpy. Hypersonic wind tunnel
refers to a wind tunnel where the Mach number range of the test section is
about 5−14, and the flow temperature is high enough to prevent the liquefaction of the test section when the isentropic expansion of the flow reaches
the above Mach number, but not high enough to produce real gas effect.
Comparing hypersonic wind tunnel with supersonic wind tunnel, the similarity is that hypersonic wind tunnel also has two types of continuous and
temporary impact. The difference is that an air heater needs to be installed in
the hypersonic wind tunnel. If the heater adopts the resistance type, the total
air temperature can be heated to about 1500 K. This temperature can prevent
the flow from liquefaction in the range of Mach number less than 14, but it
can only simulate the enthalpy value when the Mach number is less than 6
and cannot simulate the enthalpy value when the Mach number is higher in
the hypersonic range.
Wind tunnels with high enthalpy and hypersonic (Ma is about 5–20)
are simulated. At present, there is no experimental equipment that can fully
simulate the Mach number, Reynolds number, and enthalpy of the space
shuttle flight, as shown in Fig. 6.61. The Mach number of the hypersonic
wind tunnel is about 5−20 and has a high enthalpy value. Shock wind tunnel
is a kind of common hypersonic wind tunnel and is developed on the basis
of the shock tube. The shock tube is a device that generates shock waves
and compresses the experimental gas. It is a closed tube with a diaphragm
(shock diaphragm) separating the tube into two sections called a highpressure chamber and a low-pressure chamber. Before the experiment, the
driven gas with high pressure and the driven gas with low pressure are, respectively, filled in the high- and low-pressure chambers to meet the experimental
requirements, and the pressure ratio in the two chambers reaches a certain
P. Liu
high temperature up to 6000 K or even higher. Since the temperature is
higher than 600 K, the temperature rises further, gas molecules can appear
and so also the phenomena such as vibration, dissociation, and ionization,
which changes the nature of the air. The specific heat ratio no longer remains
constant but changes as the temperature changes. The perfect gas equation of
state is no longer applicable. Isentropic relationship fails. Enthalpy no longer
linearly increases with the temperature and is under the influence of the pressure at the same time. This real gas effect obviously has a considerable impact
on the aerodynamic characteristics of the shuttle. It is very difficult to fully
simulate the shuttle’s return to the various stages of flight in an experimental
facility. In the hypersonic continuous flow region, the main parameters for
simulation in the space shuttle aerodynamic test are Mach number, Reynolds
number, and enthalpy. Hypersonic wind tunnel can simulate high Mach
number (5−14) but cannot simulate high enthalpy. Hypersonic wind tunnel
refers to a wind tunnel where the Mach number range of the test section is
about 5−14, and the flow temperature is high enough to prevent the liquefaction of the test section when the isentropic expansion of the flow reaches
the above Mach number, but not high enough to produce real gas effect.
Comparing hypersonic wind tunnel with supersonic wind tunnel, the similarity is that hypersonic wind tunnel also has two types of continuous and
temporary impact. The difference is that an air heater needs to be installed in
the hypersonic wind tunnel. If the heater adopts the resistance type, the total
air temperature can be heated to about 1500 K. This temperature can prevent
the flow from liquefaction in the range of Mach number less than 14, but it
can only simulate the enthalpy value when the Mach number is less than 6
and cannot simulate the enthalpy value when the Mach number is higher in
the hypersonic range.
Wind tunnels with high enthalpy and hypersonic (Ma is about 5–20)
are simulated. At present, there is no experimental equipment that can fully
simulate the Mach number, Reynolds number, and enthalpy of the space
shuttle flight, as shown in Fig. 6.61. The Mach number of the hypersonic
wind tunnel is about 5−20 and has a high enthalpy value. Shock wind tunnel
is a kind of common hypersonic wind tunnel and is developed on the basis
of the shock tube. The shock tube is a device that generates shock waves
and compresses the experimental gas. It is a closed tube with a diaphragm
(shock diaphragm) separating the tube into two sections called a highpressure chamber and a low-pressure chamber. Before the experiment, the
driven gas with high pressure and the driven gas with low pressure are, respectively, filled in the high- and low-pressure chambers to meet the experimental
requirements, and the pressure ratio in the two chambers reaches a certain