A Numerical Comparison of the Flow in Conventional and Dual Bell Nozzles in the Presence of an Unsteady External Pressure Environment

Perigo, David; Schwane, Richard; Wong, Henry Y. W.

doi:10.2514/6.2003-4731

Cited by 21 publications

(11 citation statements)

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“…However, most of the previously reported results are from tests conducted in the absence of ambient pressure fluctuations until recently [22]. Under real-flight conditions, however, the launch vehicle experiences significant ambient pressure fluctuations while passing through the buffeting phase of flight.…”

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confidence: 84%

Effect of Ambient Pressure Fluctuations on the Dual-Bell Transition Behavior

Verma¹,

Stark²,

Haidn³

2012

48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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An experimental investigation was conducted to study the effect of ambient pressure fluctuations on dual-bell transition behavior. Back pressure fluctuations of frequency (f = 0.5, 1.0, 1.5, 2 and 3Hz) were artificially introduced inside the HASC using three magnetic valves. The dual-bell transition behavior is found to be very sensitive to P b fluctuations of magnitude > 20% which triggers a flip-flop phenomenon that is observed to continue as long as the fluctuations prevail. The tests show that for frequencies >2Hz, although significant fluctuations in P w in the nozzle extension can be felt, no full transition is achieved. This behavior too is not favorable as it can lead to a delay in transition. These preliminary test results suggest that the dual-bell nozzle can present problems in real-flight operation as the launcher experiences the buffeting phase of flight. The only solution therefore lies in increasing the DB stability corridor to a value greater than the magnitude of P b fluctuations (of 20%) so as to avoid the NPR range that will set the dual-bell into a flip-flop mode during buffeting.

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confidence: 84%

Effect of Ambient Pressure Fluctuations on the Dual-Bell Transition Behavior

Verma¹,

Stark²,

Haidn³

2012

48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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“…[6][7][8] Both the base and the extension have been designed with the method of characteristics. 6 The nozzle is characterized by a subsonic inflow boundary condition (a total temperature of 300 K and 15 (whose height is four times the nozzle exit radius), and an assigned constant back pressure on the right side (whose distance from the nozzle exit is equal to six times the nozzle exit radius). The total length of the external domain L D is equal to 0.4 m.…”

Section: Test Case Descriptionmentioning

confidence: 99%

“…In fact, the ambient environment is characterized by unsteadiness. Previous work 15,18 has shown that the base region of a typical launcher is subject to pressure oscillations of about 10% around the mean value, in the initial phase of the flight trajectory. The dominating frequencies are between 30 Hz and 100 Hz.…”

mentioning

confidence: 99%

“…The original aspect of the present study, compared to Perigo et al, 15 is that the nozzle pressure ratio is chosen in such a way that the separation point is located in the inflection region. Attention is focused on the excursion length of the separation point and on its comparison with the inflection region length.…”

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confidence: 99%

“…The excursion of the separation shock movement, which depends on this amplification factor, has a great influence on the onset of side loads, with the possible occurrence of structural fatigue. 15 The interest in the behavior of the dual bell nozzle in the presence of external pressure fluctuations is reported in few papers in literature. 15,18 In Perigo et al 15 the nozzle pressure ratio was such that the separation point and the shock system were not very sensitive to external pressure fluctuation, while in Verma et al 18 attention is focused on the possibility that an external perturbation can trigger a transition/retransition cycle (called flip-flop behavior).…”

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confidence: 99%

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Flow Separation Response to Unsteady External Disturbances in Dual Bell Nozzles

Martelli¹,

Betti²,

Nasuti³

2014

50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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The dual bell nozzle belongs to the family of Altitude Compensating Nozzles (ACN), which constitutes an option of great interest to improve launcher first stage performance. The internal flow of this nozzle adapts to the external pressure by separating at the wall inflection at low altitude (first operating mode) and by full flowing at high altitude (second operating mode). Therefore the dual bell nozzle operates with a separated flow at take off and in the initial portion of the flight trajectory. This characteristic is of important concern since the external flow is neither steady nor axisymmetric, and its coupling with the internal flow separation can cause dangerous side loads. This work presents the results of a time accurate numerical analysis of the effect of unsteady ambient pressure on the separation point and on the shock system inside the dual bell nozzle, operating in the first mode. The external computational domain is characterized by an acoustically open downstream boundary. The numerical simulations show that the oscillation of the separation point is very sensitive to frequencies near the acoustic wave characteristic frequencies

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