Contoured Rocket Nozzles

From our previous research on the side-load of the LE-7A engine, it was found that a discontinuous step in the nozzle caused large side-load. Fast movement of separation, termed was observed with such large side-load. To clarify the influence of step height and step location on the phenomenon of separation jump and on side-load peak due to the separation jump, a parametric study with cold-flow tests was conducted. Based on the test results, it was clarified that the key phenomenon ruling the separation jump is the base flow behind the step. The influence of design parameters of the step on the separation jump can be explained by the base flow characteristics. The strength of side-load was found to be related only to the location of the step. As the location of the step shifted downstream, the strength of side-load increased. Nomenclature : boundary layer thickness at 70% of nozzle length δ h : step height s x: distance from the throat x : step location s x : position of the separation sep x : distance over which the separation jumps jump L: nozzle length ca NPR: nozzle pressure ratio, P /P NPR : NPR at which nozzle flow separates at each sep position P : ambient pressure around the nozzle a P : stagnation pressure in the chamber c

The vapor-liquid equilibria with chemical reaction equilibrium of a quaternary system, acetic acid-ethanol-water-ethyl acetate, were measured in an equilibrium still by the static method. The experimental data were correlated by using the modified UNIQUAC equation to satisfy the chemical equilibrium condition as well as the vapor-liquid equilibrium condition. The UNIQUAC binary parameters were obtained from experimental vapor-liquid equilibrium data with chemical reaction equilibrium in the liquid phase of the quaternary system and existing equilibrium data for the six binary and the two ternary systems. The correlations of both the vapor-liquid equilibrium and the chemical reaction equilibrium in the liquid phase were found to be in good agreement with the experimental data.

[Abstract] During the Apollo Program, one of the critical operation considerations was the effects of a descending rocket exhaust on soils when the flight vehicles is approaching to the lunar surface. For the new exploration initiatives, it is important to re-visit the issue to ensure the safety and reliability of the vehicle descending and ascending operations. In 1966, there was a study about the soil erosion for landing rockets. Characteristic expressions of the soil erosion developed from theoretical and scaling analyses and experimental data which, along with rocket motor performance, were used to predict cratering effects during a soft earth landing. A CFD simulation software, FLUENT 6.2, was used to reproduce the experiment processes and to gain physical insight. In FLUENT, the interaction between the rocket exhaust gas and the soil surface is described by the multiphase Eulerian model. The phases can be liquid, gases, or solid (gas-solid model will be used in this study) in nearly any combination. The comparison between the existing experimental data and the new simulation results using the multiphase model is discussed.

A comparatively simple method for obtaining wall contours of supersonic nozzles of arbitrary exit cross sections from readily determined axisymmetric flows is presented. An initial axisymmetric flowfield is calculated using the method of characteristics in two dimensions from which the desired three-dimensional shape may be generated by specifying the appropriate cross section at the streamwise station giving the required overall nozzle length and exit Mach number. The describing points on the perimeter of this section are traced along corresponding streamlines back to the throat. The stream sheets formed by these streamlines then define the new nozzle contour. Elliptical and two-dimensional wedge-shaped nozzles are designed using this approach, and comparisons are reported between detailed finite-difference flowfield predictions and experimental measurement.

Complex chemical kinetics in supersonic nozzle flow

Evaluation of influential parameters for supersonic dehydration of natural gas: Machine learning approach

Chemical equilibrium for the reactive system propionic acid + ethanol + ethyl propionate + water at 303.15 and 313.15 K

Anode for a non-transferred DC plasma spray torch was designed to improve electrothermal efficiency. A theoretical calculation was made for the electrothermal efficiency in a DC plasma torch operating with argon at atmospheric pressure with power level in the range of 5.2–20 kW using energy balance equations. ANOVA for the two level factorial design was done. Plasma gas flow rate, current intensity, nozzle diameter and length were found to influence the efficiency. The efficiency was found to decrease with increase in current intensity and nozzle length and to increase with increase in nozzle diameter and gas flow rate. The overall energy balance calculations showed that the heat transfer to the plasma-forming gas decreases with increase in arc current and the same was more significant at higher flow rates. Plasma jet velocity for different flow rates, input to the torch and nozzle dimensions was calculated from the gas enthalpy. It was found that the velocity increased with increase in the power input to the torch and gas flow rate and decreased with increase in nozzle length and diameter. The current–voltage characteristics of the torch operating with argon gas were studied for different gas flow rates. The Nottingham coefficients were calculated using least – square method.

The effects of an exhaust plume and nozzle length on the flow organization of axisymmetric base flows have been studied experimentally at Mach numbers of 0.76 and 2.2 using particle image velocimetry. From the measured velocity data, the mean pressure field was computed. The application of different nozzle lengths resulted in flow cases in which the shear layer impinges on the model, on the flow downstream of the model, or intermittently on the model and on the flow. The results showed that, for intermediate nozzle lengths, the overall pressure level downstream of the base decreased in the transonic flow cases and increased in the supersonic flow cases, indicating an entrainment effect in transonic flow and a displacement effect in supersonic flow. An increase in nozzle length was found to lead to a higher local pressure at the nozzle exit, which seemed to result in more overexpanded plumes in the transonic flow cases and less underexpanded plumes in the supersonic flow cases.

This research aims at building a turbulent diffusion combustion model based on chemical equilibrium and kinetics for simplifying a complex chemical mechanism. This paper presents the combustion model based on chemical equilibrium combined with an eddy dissipation concept model (CE‐EDC); the model is validated by simulating a H2‐air turbulent diffusion flame. In the CE‐EDC model, the reaction rate of fuels and intermediate species are estimated by using the equations of the EDC model. Then, the reacted fuels and intermediate species are assumed to be in chemical equilibrium; the amounts of the other species are determined by the Gibbs free energy minimization method by using the amounts of the reacted fuels, intermediate species, and air as reactants. An advantage of the CE‐EDC model is that the amounts of the combustion products can be determined without using detailed chemical mechanisms. Moreover, it can also predict the amounts of the intermediate species. The obtained results are compared with Takagi's experimental data and the data computed by the EDC model, which uses the complex chemical mechanisms. The mole fractions of H2, O2, H2O, temperature, and velocity obtained by using our CE‐EDC model were in good agreement with the reference data without taking into account the chemical reaction rates of the O2 and H2O. Furthermore, the mole fractions of OH and H are in good agreement with the results of the EDC model at high temperatures. On the other hand, the chemical equations involving OH and H were used for predicting the mole fractions of OH and H, which were similar to those obtained from the EDC model at low temperatures. Using the present CE‐EDC model, amounts of combustion products can be calculated by using a reduced chemical mechanism and the Gibbs free energy minimization theory. The accuracy of this model is in the same order as that of the EDC model. The CE‐EDC model uses reduced chemical mechanism concerning selected species, while the result of the chemical equilibrium calculation was employed to the other species; further, the accuracy of the CE‐EDC model is the same as that of the EDC model as to major species, T, U, and k. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20296

This paper describes in detail the assessment of the CFD code CFX to predict adiabatic liquid-gas two-phase bubbly flow. This study has been divided into two parts. In the first exercise, the effect of Lift Force, Wall Force and the Turbulent Diffusion Force have been assessed using experimental data from the literature for air-water upward bubbly flows through a pipe. The data used here had a characteristic near wall void peaking which was largely influenced by the joint action of the three forces mentioned above. The simulations were performed with constant bubble diameter assuming no bubble interactions. This exercise resulted in selection of the most appropriate closure form and closure coefficients for the above mentioned forces for the range of flow conditions chosen. In the second exercise, the One-Group Interfacial Area Transport equation was introduced in the two-fluid model of CFX. The interfacial area density plays important role in the correct prediction of interfacial mass, momentum and energy transfer and is affected by bubble breakup and coalescence processes in adiabatic flows. The One-Group Interfacial Area Transport Equation (IATE) has been developed and implemented for one-dimensional models and validated using cross-sectional area averaged experimental data over the last decade by various researchers. The original one-dimensional model has been extended to multidimensional flow predictions in this study and the results are presented in this paper. The paper also discusses constraints posed by the commercial CFD code CFX and the solutions worked out to obtain the most accurate implementation of the model.

The traditional methods of Lunar/Martian rocket plume-dust simulation lack essential physics and feasibility for realistic application. The challenges arise from plume impingement flow in extra-terrestrial environment and peculiar granular behavior of irregular regolith. This paper presents significant improvement in the physics of plume-surface interaction, soil erosion and debris release through Eulerian multiphase modeling. In this approach, the rocket exhaust gas and regolith phases are coupled with inter-phase momentum and energy exchanges. Appropriate new formulations of granular flow kinetics are developed for poly-dispersed, irregular particles. The surface stresses for plume scouring and regolith roughness are refined by appropriate turbulence modeling. The numerics are built upon high-performance, adaptive mesh refinement architectures. Validation studies and applications will include cratering experiments with sand, Moon/Mars regolith simulants, reduced gravity effects and various Moon/Mars landing scenarios. This tool will provide a basis for deeper understanding of extra-terrestrial debris impact and mitigation measures for future space exploration systems.

The length of the entry blackout period during descent of the Viking Lander into the Mars atmosphere is predicted from calculated profiles of electron density in the shock layer over the aeroshell. Nonequilibrium chemistry plays a key role in the calculation, both in the inviscid flow and in the boundary layer. This is especially true in the boundary layer contaminated with ablation material, for which nonequilibrium chemistry predicts electron densities two decades lower than the same case calculated with equilibrium chemistry.

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

A comparison of homogenous and separated flow assumptions for adiabatic capillary flow