Ludwieg tube

A Ludwieg pipe is a cheaper and simpler experimental setup to produce supersonic and hypersonic flows. Mach numbers up to 4 can be reliably achieved without additional heating; with a preheating of the expansion gases Mach numbers to 11 can be achieved.

Operation

A Ludwieg pipe is a wind tunnel, allowing the short-term measurements in over-or hypersonic flows. A large evacuated pressure vessel is separated by a fast-switching valve or a diaphragm behind a convergent- divergent nozzle connected ( before the nozzle arrangement is also possible). There is a long cylindrical tube having a cross-section is significantly larger than the cross section of the nozzle on the other side of the nozzle. For commissioning the pressure is increased in the expansion tube and - if necessary - the gas heated. To start the measurement, the valve is suddenly opened and the diaphragm destroyed ( mechanically by a pointed body ). This forms in the vacuum tank, a shock wave, and a rarefaction wave runs into the expansion tube. While forming a subsonic flow in the direction of the nozzle in the pressure accumulator ( expanding tube), where the gas is accelerated in the supersonic. The resulting flow is stationary, until the expansion fans is reflected by the rear end of the expansion pipe and reaches the nozzle. Typical measurement times are of the order of 100 milliseconds, which is sufficient for most measurements.

History

The Ludwieg tube was invented by Hubert Ludwieg (1912-2000) in 1955. He developed it as a contribution to a contest in which the design of a transonic or supersonic channel should be developed which can reach high Reynolds numbers to small operating costs. Professor Ludwieg demonstrated and explained to the strong influence of the sweep of wings in the transonic region on the flow resistance (Dissertation of 1937).