How to Calculate the Size of a Thrust Augmenter

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Bruno Ogorelec
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How to Calculate the Size of a Thrust Augmenter

Post by Bruno Ogorelec » Tue Aug 24, 2004 5:38 pm

The thrust augmenter is a device that mixes cool air into the hot gas jet of a pulsejet and greatly increases its thrust. It is simple to build and not terribly sensitive to exact measures. A reasonable approximation of the relations given here will be sufficient. Look at the illustration at the bottom to locate the elements depicted by the following symbols:

dj – Exhaust tube diameter

D – Ejector tube diameter

delta – Distance between exhaust tube and augmenter mouth (sorry, this program does not appear to support greek letters)

R – Radius of the augmenter lip

L – Length of augmenter

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dj is the starting parameter. Others are calculated from its value as follows:

delta = 2 dj

D = 2.5 to 3 dj

L = 10 dj

R = 0.25 D

The end of the ejector can be flared (to an arbitrary fraction of L -- indeed, even the entire duct can be conical) and the internal angle of flare should not be more than 5 degrees from centerline.
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