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7/22/2019 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
7/22/2019 Plug Aero Spike
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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