Linear Plug Nozzle Research Articles

Numerical Analysis of Flowfield in Linear Plug Nozzle with Base Bleed

A linear aerospike nozzle is a kind of altitude adaptive nozzle that has optimum performance over the entire operational range. In this work, flow characteristics of a linear plug nozzle and a truncated plug with 40% plug length are studied numerically. Different flow types associated with an increase in nozzle pressure ratio, corresponding wall pressure variation and shock patterns are studied. The effect of base pressure improvement with a secondary flow from the base (base bleed) of the truncated nozzle is also examined. Four base bleed points are considered, and the optimum bleed point is selected based on performance and base pressure improvement. The two-dimensional numerical model is solved using Reynolds-averaged Navier–Stokes equations with the Transition SST turbulence model. Validation shows that the present model is good enough at predicting the flow features associated with a linear plug nozzle. From the three different flow types associated with this nozzle, the transition from one type to other happens at lower nozzle pressure ratios with truncation due to the reduction in length of the plug. Thrust coefficient increased by 3.54% in the case of the bleed 3 configuration with a secondary flow of 2% of inlet mass flow rate when compared with 40% plug length without base bleed.

Effect of clustering on linear plug nozzle flow field for overexpanded internal jet

Experiments were carried out to analyze the flow field development of a linear plug nozzle wherein the internal nozzle was operating in the overexpanded regime. Steady and unsteady pressure measurements were taken along with the schlieren and oil flow visualization techniques to describe the flow field. Over the range of pressure ratios considered, the overexpanded shock pattern from the internal nozzle has been explained with regard to differential end conditions on either side of the core jet. The unsteady characteristics of the pressure fluctuations have been discussed with respect to the foot of the overexpansion shock on the plug surface. The effect of internal nozzle clustering on the plug nozzle flow field has been studied for two different cluster nozzles. The cluster module jet wave interactions along the spanwise direction have been explained with respect to the limiting streamline pattern on the plug surface. In addition to these, the base flow characteristics for these overexpanded internal nozzle pressure ratios have been discussed for two different truncated plug lengths.

Flow Investigation of Linear Cluster Plug Nozzle

Computational and experimental tools have been used to understand the linear cluster plug nozzle flowfield for a range of pressure ratios. The experimental cluster configuration is arrived at from a linear plug nozzle by introducing splitter plates in the primary nozzle, and computational analysis of corresponding geometry is also carried out. The flow development on the plug surface has been analyzed for two different cluster module spacings. The interactions between the cluster module jets is a complex one with a three-dimensional shock structure because of the differential end condition the shock experiences on the plug wall and freejet boundary. A prominent streamwise vorticity resulting from curvature of the shock is also seen along the length of the plug downstream of the module junctions. The out-of-phase wave interactions occurring along the module centerline and the splitter plate centerline, resulting in a wavy surface-limiting streamline pattern, particularly at lower pressure ratios, is explained.

Flowfield Analysis of Linear Plug Nozzle

Flowfield Analysis of Linear Plug Nozzle

Flowfield Analysis of Linear Plug Nozzle

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Performance Analysis of an Infinite Array Linear Clusterd Plug Nozzle

I N the challenge of realizing a new generation of space launchers, either single or two stage to orbit, an important role is played by the performance of the engine expansion system working in a varying pressure environment. In this framework a great interest has been devoted to the linear plug nozzle, which has been the subject of several studies in the last decade [1–6]. The plug nozzle is an external-expansion nozzle that yields self-adaptation of the exhaust jet to varying ambient pressure ratios, in a certain range of the launcher trajectory. This self-adapting capability allows high nozzle expansion ratios while avoiding the risks of flow separation that would exist in equivalent bell nozzles. The plug nozzle is made of a primary internal expansion nozzle, which is a conventional supersonic nozzle, and an external-expansion ramp, referred to as the plug surface. Most of the different engineering solutions proposed for plug nozzles have the following common feature: the primary expansion is made through a cluster of bell nozzles (or modules) exhausting onto a common linear plug surface [7–9]. The primary nozzle partitioning allows easier manufacturing, lower thermal loads, easier cooling and higher thrust vector capability. However, clustering causes additional performance losses due to three-dimensional flow inside the modules and to the interaction of jets exhausting from adjacent modules. For these reasons the three-dimensional features have to be studied in depth to better predict the engine performance and the expected mechanical and thermal loads for nominal operating conditions both at sea level and altitude and for differentially throttled modules as well. In fact, the thrust vectoring could be achieved by differential throttling of modules and, when thrust requirement is reduced in the final part of the ascent, some of the modules could be intentionally shut down. To this goal, the present paper studies by numerical simulation, the three-dimensional flowfield generated by themodules on a reference linear plug surface. The attention is focused on the effects of the three-dimensional flow features that take place when two different kind of modules are considered: the first module is obtained by dividing the reference two-dimensional primary nozzle by vertical walls and the second one is a full three-dimensional round-to-square nozzle. The performance analysis of these different module configurations allows weighing separately the role of clustering (i.e., just divide the primary nozzle into modules with infinitely thin flat walls) and the role of module design. A further subject of this study is the analysis of the effects produced by the shut down of a module of the cluster, for both module configurations. The analysis of the different configurations is made by comparing the thrust losses with the reference two-dimensional solution.

Flowfield analysis of a linear clustered plug nozzle with round-to-square modules

The plug nozzle is one of the advanced expansion devices proposed to improve the overall performance of launcher liquid rocket engines. The present work investigates the three-dimensional flow field generated on this kind of nozzle by partitioning the primary nozzle into modules. A linear plug nozzle has been designed together with modules having two different geometries: a rectangular cross section and round-to-square module. Numerical simulations have been carried out considering the case where all modules of the primary nozzle are active and the case where one module is turned off. The solutions are compared and specific three-dimensional flow structures taking place inside the modules and on the plug are identified. The relationship between these structures and the skin friction distribution within the module and along the plug surface is investigated. Finally, the effect on performance of these three-dimensional flow features is emphasized.

Half Model Restrictions for Linear Plug Nozzle Testing

Linearplugnozzleshavebeen receivingmoreattention sincethedevelopment ofthesinglestageto orbitreusable launch vehicle. To clarify the fundamental features of linear plug nozzle e ow, experiments have been performed with half models because the design of the plug nozzle is symmetric. Experimental and numerical results are presented to investigate the usefulness of a half model design. The experiments were conducted on a half model without external e ow and with an external e ow at a Mach number of M1 =2. The results have been used to validate computations using Navier ‐Stokes equations provided with a Baldwin ‐Lomax turbulence model and a Degani‐Schiff correction. For comparison computations were performed for a full model subjected to the same conditions. For all of these conditions, the effects of increasing or decreasing pressure ratio have been taken into account. Nomenclature A = area A ¤ = sonic area CD = drag coefe cient CF = thrust coefe cient E = thrust coefe cient error F = thrust L = full plug length M = Mach number p = pressure T = temperature X, Y, Z = coordinates ° = ratio of specie c heats µt = tilt angle of the throat Subscripts c = chamber conditions d = design conditions e = exit nb = nozzle base nr = nozzle ramp t = throat t = stagnation conditions vb = vehicle base 1 = freestream conditions

Half model restrictions for linear plug nozzle testing

Half model restrictions for linear plug nozzle testing

Methodology to Solve Flowfields of Plug Nozzles for Future Launchers

In the development of future launchers, in particular Single Stage to Orbit (SSTO), the use of plug nozzles looks promising because of the possible improvement of performance, and therefore a capability to achieve accurate evaluations of the relevant flowfields is required. Nevertheless, due to the typical flow features, analyses performed by the common Computational Fluid Dynamics (CFD) methods lead to uncertain and time consuming results. To circumvent some of these problems, an approach based on a simple simulation model that replaces the mixing layer between nozzle jet and external flow by a contact discontinuity, was recently proposed by the authors. Following this approach, the complex calculation of the turbulent mixing of flows having different thermodynamic characteristics can be avoided, while correctly accounting for the main features of the flowfield. In this paper, this simple model has been implemented to compute linear plug nozzle flowfields at different ambient conditions and for different geometries of the plug. The expected flow behavior has been well reproduced and good agreement with the theoretical nozzle performance has been achieved, thus allowing to carry out a performance analysis for some of the main characteristic parameters.