The LDWT is an open-circuit wind tunnel, originally designed to create continuous hypersonic flow at low pressure (~10-1 -100 mbar). The concept is straightforward: There is a test chamber which is 1.5 m in diameter by ~1.5 m wide. Air (or other gas being used) is let in from one side of the test chamber through a carefully designed nozzle. At the other side of the test chamber lies a powerful vacuum pumping system.
The pumping system consists of:
1x 90kW vapour booster pump (Edwards special model 100B4)
1x Roots-type booster pump (Edwards 1R80)
3x rotary piston pumps (Edwards H1SC3000)
These can be viewed quite clearly in this view from above:
(note the chair, near the centre of the picture, for scale)
The system has been used in the past to test the aerodynamics of cones in rarified hypersonic flows. For example, it was used to test the heat transfer properties of the Mars Pathfinder aeroshell during its aerobraking maneuvers. Also, it was used to model the separation of the HyperX scramjet vehicle from a Pegasus booster at Mach 7-10. For these tests, sting effects are avoided by using a magnetic suspension balance to mainatin the model in the test position at the correct angle of attack.
This view shows the front of the test chamber, including the magnetic
suspension system:
The wind tunnel has been thoroughly cleaned inside and out since these pictures were taken, and has been re-equipped with more modern instrumentation. A more recent picture can be seen here...