engineering

Ludwieg tube

Ludwieg tube is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Ludwieg tube rather than just read about it. In short: A Ludwieg tube is a cheap and efficient way of producing supersonic flow. Mach numbers up to 4 in air are easily obtained without any additional heating of the flow.

Key takeaways

Ludwieg tube belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Ludwieg tube to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Ludwieg tube from memory before moving on to harder problems.

Reference excerpt

A Ludwieg tube is a cheap and efficient way of producing supersonic flow. Mach numbers up to 4 in air are easily obtained without any additional heating of the flow. With heating, Mach numbers of up to 11 can be reached.

Principle A Ludwieg tube is a wind tunnel that produces supersonic flow for short periods of time. A large evacuated dump tank is separated from the downstream end of a convergent-divergent nozzle by a diaphragm or fast acting valve. The upstream end of the nozzle connects to a long cylindrical tube, whose cross-sectional area is significantly larger than the throat area of the nozzle. Initially, the pressure in the nozzle and tube is high. To start the tunnel, the diaphragm is ruptured, e.g., by piercing it with a suitable cutting device, or opening the valve respectively. As always when a diaphragm ruptures, a shock wave propagates into the low-pressure region (here the dump tank) and an expansion wave propagates into the high-pressure region (here the nozzle and the long tube). As this unsteady expansion propagates through the long tube, it sets up a steady subsonic flow toward the nozzle, which is accelerated by the convergent-divergent nozzle to a supersonic condition. The flow is steady until the expansion, having been reflected from the far end of the tube, arrives at the nozzle again. For practical reasons, flow times are about 100 milliseconds for most Ludwieg tubes. For many purposes, this flow duration is sufficient. However, by taking advantage of multiple quasi-static flows between expansion wave reflections, experimentation times of up to 6 seconds can be achieved.

History The Ludwieg tube was invented by Hubert Ludwieg (1912-2000) in 1955 in response to a competition for a transonic or supersonic wind tunnel design that would be capable of producing high Reynolds number at low operating cost. Professor Ludwieg was also responsible for the experimental demonstration and explanation of the large effect of sweep on the drag of transonic wings (his dissertation in 1937).

See also Shock tube Supersonic wind tunnel Hypersonic wind tunnel

References

External links Ludwieg Tube Laboratory at the California Institute of Technology Heated Ludwieg Tube at the ZARM in Bremen, Germany Operation of a transonic Ludwieg tunnel(Video)

Illustrations

Worked examples

Example 1 — a first encounter with Ludwieg tube

Start with the simplest possible case. Write down what Ludwieg tube claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Ludwieg tube before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Ludwieg tube ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Ludwieg tube

In research: Ludwieg tube appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Ludwieg tube in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Ludwieg tube is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aerodynamics, Fluid dynamics, Wind tunnels, so understanding it makes those chapters shorter.
In everyday life: Look for Ludwieg tube outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Ludwieg tube in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Ludwieg tube means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Ludwieg tube out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Ludwieg tube in simple terms?

A Ludwieg tube is a cheap and efficient way of producing supersonic flow. Mach numbers up to 4 in air are easily obtained without any additional heating of the flow.

Why does Ludwieg tube matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Ludwieg tube?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Ludwieg tube.