plug aero spike

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AE3450 Plug/Aerospike Nozzles -1

School of Aerospace Engineering

Copyright © 2001 by Jerry M. Seitzman. All rights reserved.

• Internal expansion (converging-diverging) nozzles with

 fixed Ae

/At

have ~isentropic expansion (no shocks) for

only one value of pa/po (pe=pa)

• Problem for rocket nozzles in launch vehicles

 – large change in pa

with altitude

 – only get near optimum

thrust for small range of pa (pe≈ pa)

Standard Atmosphere

0.1

1

10

100

0 10 20 30

Altitude (km)

   P  r  e  s  s

  u  r  e

   (   k   P  a   )   design pe

 – bigger thrust loss when

overexpanded(low altitude)

overexpanded

under-expanded

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AE3450 Plug/Aerospike Nozzles -2

School of Aerospace Engineering

Copyright © 2001 by Jerry M. Seitzman. All rights reserved.

• Alternate approach

 – nozzle geometries where expansion is controlled more by

ambient pressure rather than nozzle walls

• Plug/Spike nozzle

 – flow expands alongcontoured centerbody

 – external outer wall ends at

(approx.) throat – design condition (pa,design),

expansion waves intersect

centerbody tip, ~1-d flow

1st use: Me 262

WW II turbojet

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AE3450 Plug/Aerospike Nozzles -3

School of Aerospace Engineering

Copyright © 2001 by Jerry M. Seitzman. All rights reserved.

• pa<pa,design (underexpanded) “under”

“over”

• Expansion controlled by pa, not by nozzle walls

 – p=pa before plug ends

 –   weak 

shocks and expansions downstream – better than CD in “overexpanded” case

   T   h  r  u  s   t

pa (back pressure)

CD Nozzle

Plug Nozzle

Designpa 

 – ptip = pa,design, keeps expanding

 – no shocks, slight flow misalignment

• pa>pa,design (overexpanded)

• Problem: keeping spike/plug cool

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Plug/Aerospike Nozzles -4

School of Aerospace Engineering

Copyright © 2001 by Jerry M. Seitzman. All rights reserved.

Lockheed-VentureStar test (2001)

• Cut-off end of plug/spike

 – flat ended plug

• Flow lower temperature

(coolant) through plug

 – cools plug and preventsrecirculation in plug wake

 – inner flow “takes the place”of the rest of the plug

From Hill and Peterson (4451 text)

• Linear Aerospike engine

 – uses modular arrays ofcombustors to form 2-daerospike