Conventional Bell Nozzles Research Articles

PIV And Schlieren Measurements Of A Linear Plug Nozzle Jet Interacting With External Flow

Plug nozzles represent a promising concept as part of a propulsion system for space launchers. The ability to adapt the nozzle jet to the ambient pressure level improves thrust performance in overexpanded operating conditions compared to conventional bell nozzles. In this study, the dynamics of a jet flow of a cold air plug nozzle model are investigated by means of PIV and high-speed schlieren measurements. For a fixed nozzle pressure ratio, the jet flow is studied in an externalouter flow environment with sub-, trans-, and supersonic Mach numbers. The effect of plug truncation is analyzed as well. It is found that the outer Mach number strongly influences the flow pattern, local velocity magnitudes and aerodynamic modes. The frequency and dominance of vortex shedding and jet screeching modes are found to be highly dependent on the Mach number of the surrounding flow. A truncated plug introduces local accelerations in its base wake region, causing an increased shock strength in the jet structure. In addition,it causes severe periodic fluctuations in the flow that are transmitted to the shear layer and induce acoustic wave emissions. The impact of the plug length on the flow dynamics has been seen to decrease with increasing outer Mach number.

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.

Numerical Analysis of Aerospike Engine Nozzle Performance at Various Truncation Lengths

The aerospike engine was first devised in the early 1960s where it provided new means of reaching orbit in a single stage. The paper aimes to demonstrate the viability of the technology by showcasing the increased nozzle thrust efficiency over the conventional bell nozzle. Various truncations were applied to the nozzle and each was subjected to two conditions, an over-expansion and near optimum condition. The nozzle contour was developed using the simple approximation method and was chosen to replicate that of the XRS-2200. This anchored the data, thereby validating the computational fluid dynamics (CFD) simulation. Simulations were completed for at nozzle pressure ratios (NPR) of 58 and 15. Velocity vector plots and contours were generated in which the recirculation region can be clearly identified. This region is a result of the negative thrust contribution of the base and grows increasingly negative when the truncation applied increases in addition to when the exhaust flow is over-expanded. The results demonstrate the performance gain of the full-length aerospike nozzle, , over all other truncations. At NPRs of 58 and 15 it showed 1.5% and 10.3% gain respectively in the nozzle thrust efficiency compared to . There are, many impracticalities related to the full-length aerospike including cooling on the nozzle. Therefore, provide a realistic nozzle truncation that would be implemented. Although radical design changes to the rocket will be required for the adaptation of the aerospike engines, the changes will be beneficial in the long term. By increasing the nozzle thrust efficiency compared to bell nozzles, less fuel will be required per launch. Furthermore, removing the multi-stage method currently used, overall, the rocket will have an increased reliability due to its reduced complexity.

Study of Conical Aerospike Nozzles with Base-Bleed and Freestream Effects

Conical aerospike nozzles are advanced rocket nozzles suitable for altitude compensation. A spike nozzle has geometry that resembles a conventional bell nozzle turned inside out. Lack of a solid outer surface ensures the variation of gas expansion to match the prevailing atmospheric pressure at different altitudes. This study focuses on flow characteristics within conical aerospike nozzles with different levels of truncation and flow conditions. Full spike and truncated aerospike nozzles are numerically simulated using two-dimensional axisymmetric and full three-dimensional models. Reynolds-averaged Navier–Stokes equations are solved with the shear stress transport turbulence model. Computational results of 20, 40, and 60% truncated nozzles are studied in comparison. Base bleed is implemented at two different locations of the base in 20% aerospike nozzle. Base bleed is taken as 2% of the inlet mass flow. The freestream effect is applied to 40% aerospike nozzle for validation purpose and 20% aerospike nozzle with different base-bleed cases for evaluation. Comparison of results establishes that the introduction of base bleed assists in compensating performance loss due to truncation, with the location of bleeding playing a major role in performance improvement. Effects of freestream on the base pressure characteristics of the nozzle are also demonstrated in comparison to nozzles without freestream.

Numerical Parametric Analysis of Dual-Bell Nozzle Flows

Dual-bell nozzles permit two different operating modes, which provide higher performance than conventional bell nozzles when applied to rocket engines operating from sea level. During the low-altitude mode, the flow is separated and the separation line is located near the inflection of the nozzle wall, in a region characterized by a negative value of the wall pressure gradient, as in conventional nozzles, and in which side loads may occur. The characteristics of this region in hot full-scale applications are addressed by means of numerical simulations, and scaling laws are sought for cold subscale side-load experiments. Moreover, the flow behavior during the transition between the two operating modes is analyzed by time-accurate simulations.

Numerical flowfield analysis of the next generation Vulcan nozzle

For numerical simulations of reacting, viscous nozzle flows in advanced rocket nozzles, a numerical method has been developed. The code is based on the well-established DLR Euler/thin layer Navier Stokes code NSHYP that was originally written for hypersonic re-entry flow simulations. The code solves the three-dimensional, time-dependent Euler and thin-layer Navier- Stokes equations in conservation-law form. Hydrogen and oxygen are considered as fuel and oxidizer, respectively. The passive scalar approach accounts for the multicomponent diffusion effects. Turbulent transport is described with an algebraic eddy-viscosity, and a &-e two-equations model. Calculations of conventional bell nozzles were performed. Results of Vulcan Mark 1 nozzle flow simulations are shown and compared in detail with another wellestablished numerical approach, based on the method of characteristi cs. A modified Vulcan engine is proposed, where the gas generator exhaust gases are injected into the main nozzle. Results of an engine analysis are presented. Based on this engine analysis, numerical flowfield calculations of the modified nozzle were performed and are presented.