Centre for Hypersonics

X2 banner

This is the next generation super-orbital expansion tube after X1.  It is capable of operating at similar conditions to X1 but has a larger diameter (85 mm) facilitating larger models.  The driver section in X2 has a compound piston allowing for a shorter compression tube than would be otherwise necessary.

Details
  • A pilot expansion tube designed and constructed to test concepts for the larger X3 tube
  • Features a compound-piston driver which consists of a light outer piston and a heavier inner piston. The latter separates from the outer piston after some initial compression and the inner piston continues down a smaller diameter compression tube to complete the driver compression process.

X2

The conditions to be expected in the flow assuming equilibrium are given in the following table:

Parameter

Moderate Enthalpy
High Enthalpy (Nitrogen)
Free-stream
Normal Shock
Freestream
Normal Shock

Pressure (kPa)

67
1890
3.3
220

Temperature (K)

4900
8500
4800
11500

Density (kg/m3)

0.046
0.52
0.0022
0.030

Enthalpy (MJ/kg)

27
27
61
61

Velocity (km/s)

6.55
0.6
10.3
0.7

Mach Number

4.8
0.3
7.3
0.2

Diss. fraction N2

-
0.47
0.06
1.0

Ion. fraction N

-
-
-
0.06
Shock Standoff Distances for Spheres

X2 was used in 2011 to measure standoff distances at conditions that are representative of re-entry of objects into the earth's atmosphere. As a baseline test case for analytical and CFD modelling, a 60 mm diameter sphere was located in a 10.0 km/s flow and the resulting video is linked here.

 

Fun with Hypersonics - World's Fastest Sports Balls

To demonstrate the flow that would occur if a golf ball was hit really, really hard, a golf ball was held in the test section of X2 and a flow of 8.4 km/s was passed over it. A video was taken with the high speed camera at a 125 kHz sampling rate. After the steady flow when the shock standoff distance remains constant,  you can see small pieces of the mylar diaphragm (that initially separates the test gas in the shock tube from the acceleration gas in the acceleration tube) bouncing off the surface of the golf ball and interacting with the flow.

What we really need to do is to come up with a secret weapon to help Australia win back the Ashes from England. Therefore, a cricket ball was placed in the same flow (for an inswinging delivery). We now just need to develop a bowler who can propell a ball at this speed. We expect that this would be a difficult delivery to play.

These videos were taken during the UQ Open Day in August 2011.