Chapter 6
Hypersonic Wind Tunnels
6.1 Types of Hypersonic Wind Tunnels
Hypersonic wind tunnels are intended for studying the aerodynamics of hypersonic aircraft, space launchers, missiles, projectiles and the atmospheric re-entry
of space vehicles. In principle, there are no differences between the operation of
a hypersonic and a supersonic wind tunnel, except that the contraction ratio of the
nozzles, A/A c reaches very high values for higher Mach number, for instance an
A/A c = 586 is needed to achieve a Mach number of 10. Hence throat dimensions
are so small that two-dimensional nozzles are most often abandoned in favour of
axisymmetric nozzles. In addition, establishment of the flow requires considerable
upstream/downstream pressure ratios, approximately 3300 for Mach 10, obtained
by compressing air upstream and expanding it downstream while filling a vacuum
tank. The energy required to run such a facility makes it such that the hypersonic
wind tunnels are most often of the blow down type. The energy required for a test is
usually stored in the form of a compressed gas or a flywheel rotating at high speed
which is a time-consuming process, but then released for a very short time during the
experiment. As a result, the duration of a test is limited, from a few seconds and could
reach even several minutes, for “cold” installations, but to a hundred milliseconds
for “hot” installations.
At high Mach number adiabatic expansion in the nozzle is accompanied by an
intense cooling necessitating heating of the air to prevent liquefaction. Thus, the
minimum level of upstream temperature allowed at Mach 10 is 1100 K (~830 °C),
which leads to a temperature in the test section of 52 K (~ −220 °C), at the limit
of the liquefaction of oxygen. Such facilities, where the gas is heated just enough
to prevent its liquefaction during the expansion, are called “cold” hypersonic wind
tunnels. In such wind tunnels, the duration of the test ranges from a few seconds to
several minutes depending on the conditions of the run and the characteristics of the
components of the facility, including the diffuser.
© Springer Nature Switzerland AG 2020
B. Chanetz et al., Experimental Aerodynamics,
Springer Tracts in Mechanical Engineering,
https://doi.org/10.1007/978-3-030-35562-3_6
135
Hypersonic Wind Tunnels
6.1 Types of Hypersonic Wind Tunnels
Hypersonic wind tunnels are intended for studying the aerodynamics of hypersonic aircraft, space launchers, missiles, projectiles and the atmospheric re-entry
of space vehicles. In principle, there are no differences between the operation of
a hypersonic and a supersonic wind tunnel, except that the contraction ratio of the
nozzles, A/A c reaches very high values for higher Mach number, for instance an
A/A c = 586 is needed to achieve a Mach number of 10. Hence throat dimensions
are so small that two-dimensional nozzles are most often abandoned in favour of
axisymmetric nozzles. In addition, establishment of the flow requires considerable
upstream/downstream pressure ratios, approximately 3300 for Mach 10, obtained
by compressing air upstream and expanding it downstream while filling a vacuum
tank. The energy required to run such a facility makes it such that the hypersonic
wind tunnels are most often of the blow down type. The energy required for a test is
usually stored in the form of a compressed gas or a flywheel rotating at high speed
which is a time-consuming process, but then released for a very short time during the
experiment. As a result, the duration of a test is limited, from a few seconds and could
reach even several minutes, for “cold” installations, but to a hundred milliseconds
for “hot” installations.
At high Mach number adiabatic expansion in the nozzle is accompanied by an
intense cooling necessitating heating of the air to prevent liquefaction. Thus, the
minimum level of upstream temperature allowed at Mach 10 is 1100 K (~830 °C),
which leads to a temperature in the test section of 52 K (~ −220 °C), at the limit
of the liquefaction of oxygen. Such facilities, where the gas is heated just enough
to prevent its liquefaction during the expansion, are called “cold” hypersonic wind
tunnels. In such wind tunnels, the duration of the test ranges from a few seconds to
several minutes depending on the conditions of the run and the characteristics of the
components of the facility, including the diffuser.
© Springer Nature Switzerland AG 2020
B. Chanetz et al., Experimental Aerodynamics,
Springer Tracts in Mechanical Engineering,
https://doi.org/10.1007/978-3-030-35562-3_6
135