Role of Wall Shape on the Transition in Axisymmetric Dual-Bell Nozzles

Nasuti, Francesco; Onofri, Marcello; Martelli, Emanuele

doi:10.2514/1.6524

Cited by 60 publications

(30 citation statements)

References 6 publications

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“…1b). This flow condition was first identified by Nasuti et al [5] as the sneak transition and occurs between the two modes of dual-bell operation [5][6][7]. At a certain altitude when the design transition nozzle pressure ratio (NPR; P 0 ∕P a ) is achieved, the separation front jumps downstream and attaches itself close to the nozzle exit and a full forward transition is achieved (Fig.…”

Section: Introductionmentioning

confidence: 91%

“…Since the early 1990s, a lot of computational [5,9] and experimental [6][7][10][11][12][13][14][15] studies have been initiated to understand the various flow phenomenon associated with DB operation and looked for possible means to control them. The renewed interest in this nozzle research is primarily due to the fact that the DB nozzle is the most promising and feasible candidate for an altitude-compensating cryogenic main engine.…”

Section: Introductionmentioning

confidence: 99%

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Unsteady Flow Conditions During Dual-Bell Sneak Transition

Verma

Hadjadj

Haidn

2015

Journal of Propulsion and Power

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A cold-gas test campaign was conducted on a subscale dual-bell nozzle operating under sea-level conditions to study the unsteady flow conditions encountered during sneak transition, which is a phenomenon prevalent just before final transition occurs. The study reveals that the flow during sneak transition is highly unsteady and is the major source of side-load generation in the dual-bell nozzle preceding the final transition. Statistical analysis suggests that, as the separation front moves into the region of wall inflection, the separated shear layer gradually comes in close proximity to the nozzle extension wall that alters the flow development process in the recirculation/backflow region considerably. This sets the entire backflow region into pressure fluctuations, making the flow conditions highly unsteady. It is further observed that the flow during sneak transition is associated with low frequencies in the vicinity of the separation location (0.8 kHz), which decreases as the sneak transition nozzle pressure ratio is approached (0.2 kHz).Nomenclature α e = wall angle at nozzle exit, deg _ m = mass flow rate of test gas, kg∕s P a = ambient pressure, bar P w = local wall pressure, bar P 0 = stagnation pressure of the test nozzle, bar r t = radius of nozzle throat, mm X = coordinate along the nozzle axis, mm α i = wall angle at the inflection point, deg α P = skewness coefficient; 1 n P n i0 P w i − P w 3 ∕σ 3 w β P = kurtosis coefficient; 1 n P n i0 P w i − P w 4 ∕σ 4 w ∈ = area ratio of the dual-bell nozzle ∈ b = area ratio of the base nozzle ∈ s = area ratio of the location of flow separation σ w = standard deviation of wall pressure fluctuations; P n i0 P w i −P w 2 n−1 r σ w ∕P w max = nondimensionalized peak value of standard deviation in the region of separation φ = angle in circumferential direction, dege

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Section: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Unsteady Flow Conditions During Dual-Bell Sneak Transition

Verma

Hadjadj

Haidn

2015

Journal of Propulsion and Power

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“…This kind of geometry is referred to as Linearly Increasing wall Pressure (LIP) dual bell nozzle and it has been widely studied in previous works of the authors. [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).…”

Section: Test Case Descriptionmentioning

confidence: 99%

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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“…Nasuti et al [11] and Martelli et al [12] studied the mode transition process of dual bell nozzles numerically with the focus on side load generation and its scalability. They identified a Reynolds number effect on inflection region length and mode transition duration.…”

Section: Introductionmentioning

confidence: 99%

Flow separation in rocket nozzles under high altitude condition

Stark

Génin

2016

Shock Waves

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The knowledge of flow separation in rocket nozzles is crucial for rocket engine design and optimum performance. Typically, flow separation is studied under sealevel conditions. However, this disregards the change of the ambient density during ascent of a launcher. The ambient flow properties are an important factor concerning the design of altitude-adaptive rocket nozzles like the dual bell nozzle. For this reason an experimental study was carried out to study the influence of the ambient density on flow separation within conventional nozzles.

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Role of Wall Shape on the Transition in Axisymmetric Dual-Bell Nozzles

Cited by 60 publications

References 6 publications

Unsteady Flow Conditions During Dual-Bell Sneak Transition

Unsteady Flow Conditions During Dual-Bell Sneak Transition

Flow Separation Response to Unsteady External Disturbances in Dual Bell Nozzles

Flow separation in rocket nozzles under high altitude condition

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