Experimental Study on Flow Transition in Dual Bell Nozzles

Nürnberger-Génin, Chloé; Stark, Ralf

doi:10.2514/1.47282

Cited by 54 publications

(24 citation statements)

References 5 publications

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“…For all cases, the maximum velocity is reached in the middle of the contour inflection. This agrees with the experimental observations [4]. After reaching the maximum, the velocity decreases again until the exit plane of the nozzle is reached.…”

Section: Transient Transition Behaviorsupporting

confidence: 89%

“…The location and angles of the shock pattern were extracted from the schlieren images and used for validation of the numerical results. Detailed information about the experimental setup is given by Génin and Stark [4].…”

Section: Methodsmentioning

confidence: 99%

“…The flow separates at the vicinity of the contour inflection point. At NPR 38, the so-called sneak transition [4] starts. The flow separation position slowly moves inside the nozzle extension.…”

Section: B Steady-state Transition Behaviormentioning

confidence: 99%

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Numerical Investigation of Flow Transition Behavior in Cold Flow Dual-Bell Rocket Nozzles

Schneider

Génin

2016

Journal of Propulsion and Power

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The dual-bell nozzle is an altitude-adaptive nozzle concept. It combines the advantages of a nozzle with small area ratio under sea-level conditions and a large area ratio nozzle under high-altitude conditions. Reynolds-averaged Navier-Stokes and unsteady Reynolds-averaged Navier-Stokes simulations on two-dimensional axisymmetric grids were conducted at DLR, German Aerospace Center in Lampoldshausen to investigate the transition from one mode to the other of a dual-bell nozzle model with positive pressure gradient extension. A cold flow test campaign conducted at DLR's cold flow test facility P6.2 provided validation data for the numerical approach. The present study investigates the influence of different turbulence models and feeding pressure gradients on the dual-bell flow transition behavior. Better results were achieved for the Spalart-Allmaras and Reynolds stress turbulence model. A clear impact of the feeding pressure ramp on the dual-bell transition pressure ratio and the flow separation position velocity was shown. The transition nozzle pressure ratio was predicted with an accuracy of 1%. For the hysteresis between transition and retransition nozzle pressure ratio, an accuracy of approximately 10% was reached. The calculated values of the experimental and numerical transition duration were on the same order of magnitude. Nomenclature A = area, m 2 H = hysteresis gap, % L = length, m R = radius, m y = dimensionless wall spacing α = angle, deg ϵ = expansion ratio Subscripts b = base nozzle e = nozzle extension i = inflection retr = retransition t = total th = nozzle throat tr = transition

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Section: Transient Transition Behaviorsupporting

confidence: 89%

Section: Methodsmentioning

confidence: 99%

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Numerical Investigation of Flow Transition Behavior in Cold Flow Dual-Bell Rocket Nozzles

Schneider

Génin

2016

Journal of Propulsion and Power

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“…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%

“…A lot of useful studies have been conducted in the past and have added vital information in understanding the various factors on which the characteristics of DB transition depend on, such as the wall inflection angle, length, and contour of the nozzle extension; film cooling in the vicinity of the wall inflection; etc. [8,9,15]. However, none of these studies, other than that of Proshchanka et al [16], focuses on the unsteady flow physics prevalent specifically during the phase of sneak transition, which forms an important part of the flight condition between the two operational modes.…”

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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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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