International Journal of Aerospace Engineering

Volume 2017 (2017), Article ID 4768376, 13 pages

https://doi.org/10.1155/2017/4768376

## Three-Dimensional Numerical Analysis of LOX/Kerosene Engine Exhaust Plume Flow Field Characteristics

Department of Space Equipment, Equipment Academy, Beijing 101416, China

Correspondence should be addressed to Wan-sheng Nie

Received 28 November 2016; Accepted 1 August 2017; Published 5 November 2017

Academic Editor: Wen Bao

Copyright © 2017 Hong-hua Cai et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

Aiming at calculating and studying the flow field characteristics of engine exhaust plume and comparative analyzing the effects of different chemical reaction mechanisms on the engine exhaust plume flow field characteristics, a method considering fully the combustion state influence is put forward, which is applied to exhaust plume flow field calculation of multinozzle engine. On this basis, a three-dimensional numerical analysis of the effects of different chemical reaction mechanisms on LOX/kerosene engine exhaust plume flow field characteristics was carried out. It is found that multistep chemical reaction can accurately describe the combustion process in the LOX/kerosene engine, the average chamber pressure from the calculation is 4.63% greater than that of the test, and the average chamber temperature from the calculation is 3.34% greater than that from the thermodynamic calculation. The exhaust plumes of single nozzle and double nozzle calculated using the global chemical reaction are longer than those using the multistep chemical reaction; the highest temperature and the highest velocity on the plume axis calculated using the former are greater than that using the latter. The important influence of chemical reaction mechanism must be considered in the study of the fixing structure of double nozzle engine on the rocket body.

#### 1. Introduction

Engine exhaust plume brings a variety of problems for the design and launch of rocket, such as [1] (1) the bottom convective heat transfer problems; (2) the bottom radiation heat transfer problems; (3) the radar signal attenuation problem; and (4) the ground thermal shock problem during the take-off of the rocket. The study of rocket engine exhaust plume flow field characteristics has the following important application value [2]: (1) the obtaining mature theory and method which can be used to help study tracking large missile [3, 4] and (2) studying the attenuation effect of exhaust plume on radio frequency communication signal [5].

Using CFD (Computational Fluid Dynamics) software for exhaust plume flow field calculation has the significant advantages, such as three-dimensional numerical simulation, choosing the turbulence model, obtaining detailed flow field parameters, and so on; it has been widely developed and applied. William and Calhoon’s simulation [6] analyzed the rocket exhaust plume flow field using the structured and compressible N-S flow solver software GASP (the General Aerodynamic Simulation Program); the simulation study of Saturn V heavy-lift launch vehicle plume was carried out [7] using the CFD calculation procedures—OVERFLOW. Staged calculation method [2] was used to calculate exhaust plume flow fields: first, get the stagnation temperature and other parameters which can be the inlet boundary condition of second stage using the CEA (Chemical Equilibrium with Applications) from NASA for the zero-dimensional numerical analysis and then calculate exhaust plume flow fields with CFD software FLUENT. Three-dimensional numerical simulation of pure gas-phase single-nozzle [8] and four-nozzle [9] exhaust flame flow fields was calculated using the method of large eddy simulation (LES) under the premise of ignoring the chemical reaction influence. FLUENT was used to validate the simplified flow field model of Tomahawk cruise missiles BGM-109 [10]. The method of exhaust plume flow field calculation above is conducted without considering the influence of internal combustion state on exhaust plume flow field characteristics. Cai et al. and Feng et al. [11, 12] developed an integrated calculation method of the inner flow field and the plume field of the engine; the effects of combustion chamber combustion model and the nozzle inside surface type on the plume flow field characteristics were studied. The integrated calculation method considered the effect of engine internal combustion state, but it needs a greater number of repeated calculations when calculating the multinozzle engine exhaust plume flow field.

In this paper, a method fully considering the combustion state influence based on the CFD software FLUENT is put forward, which is applied to exhaust plume flow field calculation of multinozzle engine. First of all, the simulation of engine internal flow field is carried out, and the nozzle throat section parameters are as the inlet boundary. Then the calculation of single-nozzle and multinozzle engine exhaust plume flow fields is carried out. Based on the method, numerical analysis of effects of different chemical reaction mechanisms on single-nozzle and double-nozzle LOX/kerosene engine exhaust plume flow field characteristics is carried out.

#### 2. Mathematical and Physical Model

##### 2.1. Governing Equations

Multicomponent chemical reaction and conservative three-dimensional N-S equations are used as the flow, the exchange of matter and energy, and the control equation of combustion of the model. The following is the general form of it.
where is the conservative variable vector; is the time variable; , , and are the convection term vector; , , and are the viscous term vector; and is the source term vector. The equation above consists quality equation, momentum equation, energy equation, and equation of components in the direction of *x*, *y*, and *z*, respectively.

##### 2.2. Chemical Reaction Mechanism

There are hundreds of components in kerosene, so it is difficult to describe the actual chemical reaction process accurately. In this paper, single-step global chemical reaction mechanism and multistep chemical reaction mechanism are studied.

The first part is the single-step global chemical reaction, and the actual combustion process of kerosene can be simplified by the alternative fuel C_{12}H_{23}, by one-step oxidation process; the reaction produces H_{2}O and CO_{2}, and the chemical reaction rate is calculated by
where is the temperature, the unit is in K; [KERO] is the molar concentration of kerosene, the unit is in ; and [O_{2}] is the molar concentration of oxygen, the unit is in . The specific values of other parameters are shown in Table 1.