Dual Bell Nozzle Research Articles

Optimizing the design of a supersonic Planar Dual Bell Nozzle (PDBN)

Dual bell nozzles present a promising solution for maximizing propulsion efficiency at high altitudes, while also mitigating dangerous side loads at lower altitudes. Such nozzles are comprised of two distinct contours, with the first optimized for low altitude operation, and the second tailored for high altitude conditions. These contours are interconnected at an inflexion point. The present study focuses on optimizing the contour design of a planar dual bell nozzle. Leveraging the commercial ANSYS-Fluent software, we conducted an investigation into the influence of the inflection angle on the transition between the two operating modes, examined the flow behavior inside the nozzle, and assessed the impact of the inflection angle on the thrust coefficient.

Результати проектування надзвукового сопла з подвійним розширенням для рідинного ракетного двигуна першого ступеня методами обчислювального аналізу

The subject of this study is dual-bell supersonic nozzles of liquid rocket engines. The goal is to design a dual-bell supersonic nozzle that will provide maximum thrust for a liquid rocket engine in the first stage of a launch vehicle by solving an optimization problem using numerical simulation methods. The goal of the study is to choose the exit pressures of each part of the dual-bell nozzle based on the known flight trajectory of the launch vehicle, set and solve the problem of optimizing the dual-bell nozzle contour, and assess the impact of the use of a dual-bell nozzle on the efficiency of a liquid-propellant rocket engine. The methods used are: numerical methods for solving the hyperbolic system of unsteady equations of gas dynamics and multidimensional minimization problems. The following results were obtained. The formulation and solution of the optimization problem of the contour of a dual-bell supersonic nozzle, considering the design limitations in the form of a fixed length of the nozzle, is carried out. By analyzing the flight path of the first stage of the launch vehicle, a first approximation of the nozzle contour was obtained. For further calculations, both sections were approximated by parabolas, the coefficients of which, together with the lengths of the sections, formed a vector of optimized parameters. An expression for the axial component of thrust with the opposite sign was used as the objective function to solve the minimization problem. Because of solving the optimization problem, a dual-bell nozzle contour was designed to provide maximum thrust. An assessment of the effectiveness of his work was also conducted. The calculated value of the average along the trajectory of the specific impulse when using a dual-bell nozzle was higher by 1.6% than when using a standard nozzle. Conclusions. The scientific novelty of the obtained results is as follows: the design of the dual-bell nozzle contour was performed by solving the problem of multidimensional optimization, taking into account the design constraints, and using computational analysis methods

Study on wall pressure and hysteresis behaviors of a novel dual-bell nozzle

Study on wall pressure and hysteresis behaviors of a novel dual-bell nozzle

Parametrical Investigation of Transverse Injection in a Dual-Bell Nozzle During Altitude-Varying Conditions

The dual-bell nozzle (DBN) is a rocket nozzle concept that could provide a substantial payload gain. The present paper focuses on the impact of radial secondary injection on DBN behavior during its ascent and descent in the atmosphere. The influence of the secondary injection settling chamber (cavity) volume is discussed. The positive influence of the cavity volume on the DBN behavior during transition phases has been exposed, and its effects during retransition were shown to be negligible. The use of secondary injection allowed the transition nozzle pressure ratio to be increased by nearly 24%, and the lateral forces were reduced to less than 1% of the nozzle thrust. A first approach regarding secondary injection optimization is finally proposed.

Design Process and Flow Field Analysis of a Double Divergent Supersonic Nozzle: Enhancing Efficiency and Performance

The dual bell nozzle concept's primary goal is to increase performance through the idea of selfadaptation for two operating regimes without mechanical activation. The dual bell nozzle type known asthe planar double divergent nozzle (DDN) has a rectangular cross section. In this study we propose anumerical method for the design of the nozzle profile with double planar divergent. The design of the doubledivergent nozzle is carried out in two parts. The first divergent is a contour of a two-dimensional supersonicnozzle with a sharp-edged throat that gives uniform parallel flow at the exit. The method of characteristicapplied to the two-dimensional isentropic flow of an ideal gas was used for the design of a supersonic planarnozzle. The contour of the second divergent (nozzle extension) is a polynomial. This is achieved using thedirect method of characteristics. A numerical analysis of a double divergent nozzle, and a planar nozzlewith the same area ratio and the same length using ANSYS-Fluent software. The analysis's findingsindicated that the double divergent nozzle had a weight decrease of 0.61%. The thrust increase is estimatedat 3.88% in the low-altitude operating mode for the double divergent nozzle.

Altitude-compensating axisymmetric supersonic nozzle design and flow analysis

Altitude-adapted nozzles are designed to facilitate flow adaptation during rocket ascent in the atmosphere, without requiring mechanical activation. As a consequence, the performance of the nozzle is significantly improved. The aim of this study is to develop a new profile of axisymmetric supersonic nozzles adapted at altitude (Dual Bell Nozzle with Central Body), which is characterized by an E-D nozzle as a basic profile. The performances obtained for this nozzle (E-D Nozzle) are then compared to those of a Plug nozzle. The E-D nozzle shows significant performance advantages over the Plug nozzle, including a 13.02% increase in thrust, knowing that the length of the E-D nozzle is half that of the Plug nozzle under the same design conditions. Finally, viscous calculations using the k-ω SST turbulence model were conducted to compare the performance of the dual bell nozzle with central body (DBNCB) and the E-D nozzle with the same cross-sectional ratio, and to assess the impact of nozzle pressure ratio (NPR) variations on the operation mode of the DBNCB. The results obtained show that the DBNCB offers the best performance in most phases of flight.

Numerical Investigation of Supersonic Flows on Innovative Nozzles (Dual Bell Nozzle)

The Dual Bell Nozzle is the most ambitious of several supersonic, altitude-compensating nozzle concepts for rocket engines. This design's objective is to enhance performance in two different evolving regimes (Sea-Level and High Altitude Mode) by self-adaptation with no mechanical control. The concept is simple in theory, but the structural efforts involved are significant. The study carried out in this paper is a simulation of the flows in this type of nozzle. Computational fluid dynamics (CFD) is increasingly used as an analytical tool in research and industry. Simulation is not a substitute for experimentation but a complement to it; it allows the analysis of the problem in real conditions (reproduce tests that are done in experimentation to better understand them and at lower cost) or, on the contrary, in extreme or marginal test conditions (extreme climates, installation defects, etc.). Through simulation, the studied system becomes more flexible. We can easily make parametric studies. Simulation almost always takes the form of a program or computer tool. These are commonly called simulation environments. Developments and progress over the past two decades have led to the emergence of a methodology that has become standard. As for any complex system, the control of a phenomenon is based on the identification and modularization of the tasks. Currently, the standard methodology divides the simulation process into four distinct tasks: geometric modeling, meshing, solving, and finally analysis and visualization. In this study, we will present a test case used to validate our computational models that will be used to optimize the profile of a dual bell nozzle. We will use the Ansys-ICEM environment to generate the meshes and the Ansys-Fluent environment to solve the equations of our models. Our results will then be compared with experimental and numerical data from our literature review.

Effect of the length of truncated nozzle with a tip on its thrust characteristics

Nowadays, for solving new problems, rocket engine nozzle developers are increasingly turning to non- traditional nozzle configurations that differ from the classic Laval one. A relatively new line in the design of supersonic nozzles is the development of the so-called bell-shaped nozzle, which, unlike the classical Laval nozzle, has a larger angle of entry into the supersonic part of the nozzle. In this case, dual bell nozzles, which have two flow expansion sections in their supersonic part, are considered. However, the effect of the length ratio of the two flow expansion sections of a truncated nozzle on its characteristics has not yet been studied. The goal of this work is to determine the effect of the length of the upstream conical supersonic section on the static pressure distribution in the nozzle and its thrust characteristics with the shape of the bell-shaped tip kept unchanged. The nozzle characteristics were studied using the ANSYS Fluent computing package. It was shown that the flow patterns in the nozzle (velocity fields) change with the length of the conical part upstream of the tip and the underexpansion degree. Under terrestrial conditions (Pн = 1 bar), all variants show a developed separation zone that starts from the corner point where the tip is connected to the conical part. In this case, the pressure on the nozzle wall is nearly equal to the ambient pressure. At a large flow underexpansion degree (P0 = 300 bar) and in low-pressure conditions conditions (Pн =0.1 bar), the flow in the tip is adjacent to the wall. At a large flow underexpansion degree, the pressure in the nozzle increases from the corner point to the tip exit, and the pressure at the tip exit increases with decreasing tip length. The nozzle thrust coefficient decreases with increasing flow underexpansion degree, and it reaches a constant value after the flow becomes adjacent to the tip wall downstream of the corner point where the tip is connected to the nozzle. At high flow underexpansion degrees, the nozzle thrust coefficient is higher for a nozzle with a longer conical part. The calculated results are in good agreement with experimental data on nozzles of this type.

Unsteady Flow in a Dual-Bell Nozzle with Displacement of an Extendible Section from the Initial to Working Position

Unsteady Flow in a Dual-Bell Nozzle with Displacement of an Extendible Section from the Initial to Working Position

Design and Development of a Cold-Flow Test-Bench for Study of Advanced Nozzles in Subsonic Counter-Flows

As advanced nozzles may offer alternative solutions to conventional nozzles for the future class of reusable launch vehicles, a critical aspect is to tailor these novel technologies to current recovery strategies, more specifically to vertical landing sustained by retro-propulsion. Researchers at Technische Universität Dresden have developed a dedicated test-bench for the vacuum wind tunnel facility, where Advanced Nozzle Concepts (ANCs), such as aerospike and dual-bell nozzles, are tested in cold-gas configuration while invested by subsonic counter-flows. The main objective of the test campaign is to evaluate the performance and altitude–compensation characteristics of such ANCs by simulating a vertical landing manoeuvre through the variation of ambient pressure experienced during the landing burn. A detailed description of design and development of the test-bench, together with preliminary results from the commissioning activities, are here offered to the reader. The force measurements, together with pressure and temperature data, contribute to evaluate thrust levels and coefficients, as well as the monitoring of the interaction between the nozzle cold-flow and the opposing free-stream. A background-oriented schlieren system allows to visualise the external flow-field. In conclusion, an outline of the upcoming test campaign and a description of the expected results is offered.

Flow and thrust characteristics of an expansion–deflection dual-bell nozzle

Expansion–deflection nozzle (EDN) and dual-bell nozzle (DBN) are the designs of altitude compensation nozzles that are currently widely studied. The cold flow subscale experiments and two-dimensional axisymmetric Reynolds-averaged numerical simulations were performed to explore the flow characteristics and the altitude compensation performance of an expansion–deflection dual-bell nozzle (EDDBN), which combines an EDN and DBN. The experimental results, supported by numerical simulation results, showed that the EDDBN is in the sea level closed mode under the experimental nozzle pressure ratios. The transition characteristics of the EDDBN and the DBN were simulated by continuously changing the nozzle inlet total pressure. In wider ranges of nozzle pressure ratios, owing to the lower wall pressure of the extension nozzle, the EDDBN has a higher mode transition pressure ratio than the DBN. Compared with the DBN with the same design pressure ratio, the EDDBN can further improve the thrust performance of the exhaust system during the mode transition, confirming the application value of the proposed nozzle design.

Dual-bell nozzle with fluidic control of transition for space launchers

The dual-bell nozzle is a promising concept for improving the performance of space launchers. It is characterised by the presence of two altitude-dependent working modes which allow to reduce non-adaptation losses. However, the transition between the two working modes usually takes place prematurely and dangerous side loads might be observed. In this work, fluidic control is investigated as a potential method to delay the transition and limit the risk of side loads. A launcher configuration similar to the Ariane 5 with a dual-bell nozzle in the core engine is considered. First, a parametric optimisation is performed to identify the dual-bell geometry that maximises the payload mass delivered into geostationary transfer: a preliminary model is adopted to describe the dual-bell mode transition and a fast and reliable in-house trajectory optimisation code is used to optimise the ascent trajectory. The flow field in the optimal geometry is then investigated by CFD simulations to verify the effectiveness of fluidic control. Finally, the CFD study results are used to model the dual-bell mode transition and trajectory optimisation is performed again. The proposed solution is characterised by a large payload gain (approximately 1.5 metric tons) with respect to the reference launcher. The simulations showed that fluidic control reduces the order of magnitude of side loads which can arise during transition, showing its potential as enabling technology for the application of dual-bell nozzles on real launchers.

デュアルベルノズル内部における剥離点の制御

Dual bell nozzle has a structure that combines two bell nozzles with different expansion ratios, consisting of a base nozzle with a low expansion ratio and an extension nozzle with a high expansion ratio. In this paper, axisymmetric two-dimensional unsteady numerical calculations were performed using two types of dual bell nozzles. There was a difference whether there is a step at inflection point of the nozzle, and the conditions for controlling separation inside the nozzle and creating a stable flow were investigated. The step size is 0.01 times the throat radius. Grid points of the nozzle were 800 in the axial direction and 200 in the radial direction. The static pressure at the outlet was set to 3kPa, and the total pressure at the inlet was linearly increased from 3kPa to 600kPa in 0.3 second. Injection of nozzle inflection point with step were set to no injection, 50 kPa and 100 kPa. The working fluid was ideal gas air. The calculation results were arranged by the nozzle pressure ratio (NPR), and the thrust coefficient and the wall pressure were compared. As a result, it was found that adding a step to the inflection point of the dual bell nozzle has little effect on the nozzle performance. In addition, the separation point inside the nozzle could be controlled by the injection from the nozzle inflection point.

Unsteady flow simulation of compressible turbulent flow in dual-bell nozzle with movement of extendible section from its initial to working position

The use of extendible nozzles in propulsion systems is one of the ways to increase the geometric degree of expansion of the nozzle and the thrust. Numerical simulation of a supersonic turbulent flow of a viscous compressible gas in an extendible nozzle is considered. The simulations performed take into account the movement of the extendible part of the nozzle from the its initial to the working position. The Reynolds-averaged Navier–Stokes equations and the equations of the SST turbulence model discretized on moving meshes are used for numerical calculations. The unsteady flowfield formed when the nozzle is brought to the working position is studied, and the topological features of the flow (separation, mixing, reattachment, secondary flow), and the spatial and temporal distributions of flow quantities are investigated. The distributions of pressure at different times and the axial force applied to the inner walls of the nozzle during the outflow of a supersonic underexpanded jet from the nozzle are discussed. The distributions of flow quantities computed with unsteady and quasi-state formulations of the problem are compared.

Computational investigation of cooling effectiveness for film cooled dual-bell exhaust nozzle for LO2/LH2 liquid rocket engines

ABSTRACT A dual bell nozzle (DBN) consists of two bell nozzles of different geometric area ratios attached at the region called inflection. This distinct geometry modification allows the nozzle to adapt to altitudes through its different operating modes. A numerical investigation with hot flow is done on a 2-dimensional axisymmetric model of a DBN having coolant injection at its inflection. Analysis has considered the secondary injection of gaseous hydrogen film into the gas mixture resulting from the combustion of liquid hydrogen and liquid oxygen in the thrust chamber of a LO2/LH2 engine. Model gave a root mean square deviation of 0.0012 from the experimental result at 30 NPR. Flow phenomena inside the nozzle are studied for different altitudes with and without coolant injection. Shift of separation location inside the nozzle on changing the quantity of gaseous hydrogen injected for three nozzle pressure ratios in the range of operation of the nozzle is calculated. The nondimensional shift in separation location is estimated to be 1.34 at 30 NPR, 1.10 at 45 NPR and 0.70 at 60 NPR. Temperature distribution on nozzle wall and cooling effectiveness of coolant on nozzle wall is determined with varying coolant mass flow rate for LO2/LH2 and LO2/RP1 rocket engines and the results are compared. The effectiveness of coolant for LO2/LH2 engine reduces from 1 to 0.78 on moving downstream of the nozzle whereas it reduces from 1 to 0.27 for LO2/RP1 engine. The study also predicts reduction in specific impulse of 5% for LO2/LH2 engine and 3.3% for the LO2/RP1 engine at MR = 15 due to the film cooling.

Supersonic Several Bells Design of Minimum Length Nozzle Contours for More Altitudes Level Adaptations

This wok focuses to develop a numerical computation program allowing to design new contours of a supersonic nozzle having several bells, adapted to several levels of different altitudes, going from sea level and progressively with the altitude up to space, giving a supersonic uniform and parallel flow to the exit section and a maximum possible thrust without loss, aiming to reduce considerably the side loads caused in the conventional and the dual bell nozzles when the ambient pressure decrease with the altitude. The first bell has a sonic, uniform and parallel inlet to the throat, and a sea level adaptation with a reduced supersonic Mach number, while the other bell have a supersonic, parallel and uniform inlet and an adaptation to a given altitude with a progressed increase of supersonic Mach number. The transition from one level of adaptation to another adjacent is done without mechanical activation. The purpose of this type of nozzle is to have the possibility of flying in several supersonic regimes adapted to several different altitudes with a reduced side loads. This type of nozzle is named by Several Bell Nozzle and has inflection points between bell and adjacent other. The design is done in the context of a calorically and thermally perfect gas. The problem is to design a typical bell having a uniform and parallel supersonic inlet and exit with two given Mach numbers. The design is made by the use of the Method of Characteristics. The resolution of the equations is done numerically by the finite difference corrector predictor algorithm. The validation of the results is controlled by the convergence of the ratio of the critical sections, calculated numerically, to that given by the theory. In this case, all the design parameters converge automatically to the desired solution. The application is made for axisymmetric MLN having 3, 4, 5 and 10 bells.

Experimental investigation of forced flow regime transition in a dual bell nozzle by secondary fluidic injection

Experiments on an axisymmetric dual-bell nozzle were performed at EDITH nozzle test facility of CNRS in Orléans, France. The main purpose of the study was to explore the possibility of controlling the flow regime transition by a secondary fluidic injection in the dual bell nozzle. The main focus of the present paper is to investigate the impact of the secondary injection parameters on the flow regimes transition in such nozzles. Secondary injection has been found to effectively control the flow regime transition and consequently to increase the propulsive performance of the device. It has also been pointed out that even a very low injected secondary mass flow rate leads to the control of the transition and contributes to reducing the lateral loads which can exist, moreover, when transitions are operated without injection.

Effect of Throttling on Dual-Bell Sneak-Transition Side Loads

An experimental investigation has been conducted on a subscale dual-bell nozzle to study the effect of throttle settings on sneak-transition side loads. The results are from a cold-gas test campaign conducted in a high-altitude simulation chamber for three throttle settings of 1, 2, and . An analysis is carried out by correlating the simultaneously acquired side-load measurements and real-time wall pressure data from transducers mounted in the vicinity of the wall inflection. The study reveals that the longer is the time duration of separation front in the region of wall inflection, the higher is the amplitude of overall sneak-transition side loads. Increasing the throttle settings from 1 to significantly reduces not only the overall sneak-transition duration but also the amplitude of flow unsteadiness in the region of wall inflection during the intermittent flow condition of the sneak transition and, hence, the associated side loads. It is further observed that even though the total transition time decreases with an increase in throttle settings, the actual transition side-load peak amplitude remains more or less similar irrespective of throttle setting.

Numerical Analysis of Side-loads Reduction in a Sub-scale Dual-bell Rocket Nozzle

A calibrated delayed detached eddy simulation of a sub-scale cold-gas dual-bell nozzle flow at high Reynolds number and in sea-level mode is carried out at nozzle pressure ratio NPR = 45.7. In this regime the over-expanded flow exhibits a symmetric and controlled flow separation at the inflection point, that is the junction between the two bells, leading to the generation of a low content of aerodynamic side loads with respect to conventional bell nozzles. The nozzle wall-pressure signature is analyzed in the frequency domain and compared with the experimental data available in the literature for the same geometry and flow conditions. The Fourier spectra in time and space (azimuthal wavenumber) show the presence of a persistent tone associated to the symmetric shock movement. Asymmetric modes are only slightly excited by the shock and the turbulent structures. The low mean value of the side-loads magnitude is in good agreement with the experiments and confirms that the inflection point dampens the aero-acoustic interaction between the separation-shock and the detached shear layer.

Controlled flow regime transition in a dual bell nozzle by secondary radial injection

With the ever rising demands for cheaper payload delivery to orbit, dual bell nozzle with a potential theoretical performance gain of up to 10% can represents one of the major ways of advance to achieve the goal. The well-known transition unsteadiness in a dual-bell rocket nozzle represents one of the major concerns for the development of such altitude compensating type nozzle (ACN). The present study proposes and investigates the possibilities of secondary radial injection for flow regime transition control. Present experimental results demonstrate potential effects of secondary injection on transition and re-transition control even with a relatively low secondary injection mass flow rates. Doing so, the transition and retransition process were significantly delayed towards the ideal transition point. In addition, side loads have been found to be greatly decreased or even eliminated.