CHAPTER-1

INTRODUCTION

Nozzle is a main component in Rocket that is used to convert the Chemical-Thermal Energy generated in the Combustion Chamber into Kinetic energy. The Nozzle converts the low velocity, High Pressure, High Temperature gas in the thrust Chamber into High Velocity gas of lower Pressure and temperature. De Laval Nozzle found that the most efficient conversion occurred when the nozzle first narrowed, increasing the speed of the jet to the speed of sound. Computational Fluid Dynamics (CFD) is an engineering tool that assists experimentation .Its scope is not limited to fluid dynamics.CFD could be applied to any process which involves transport phenomena with it. To solve an engineering problem we can make use of various methods like the analytical method Experimental methods using prototypes. The analytical method is very complicated and difficult. The experimental methods are very costly .If any errors in the design were detected during the prototype testing, another prototype is to be made clarifying all the errors and again tested.

A nozzle is a device that increases the velocity of a fluid at the expense of pressure. Nozzle is a part of rocket which is used for the expansion of combustion gases through it and produces thrust. Nozzle is a passage used to transform pressure energy into kinetic energy. During the combustion of fuel, chemical energy is converted into thermal energy and pressure energy. The combustion gases at this stage are at a high pressure and temperature and these gases under such high pressure expand through the nozzle during which the pressure energy is converted into kinetic energy which in turn moves the vehicle in a direction opposite to that of the exhaust gases, according to Newton’s third law of motion. Two primary functions of nozzle are – First, they must control the engine back pressure to provide the correct and optimum engine performance, which is done by jet area variations. Second, they must efficiently convert potential energy of the exhaust gas to kinetic energy by increasing the exit velocity, which is done by efficiently expanding the exhaust gases to the atmospheric pressure.

A new application of the CFD and optimization method is established in the present case for process development for optimization converging-diverging nozzle flow by expecting the highest level of accuracy. This work is divided into two parts. First, a validation and verification of the nozzle model using experimental and computational data is presented. Afterwards the paper deals with the optimization of nozzle contours for having the maximum thrust by using the numeric-cal model to be constructed. The nozzle optimization problem can be defined as the following: given a set of external parameters and geometric con-strains, find a nozzle wall contour such as the resulting thrust produced by the nozzle is maximal. The external parameters are: ambient pressure, temperature and chamber pressure, temperature. The geometric constraints are the nozzle length and throat diameter. Air as ideal gas has been used for the operational fluid.

Nozzle is used to convert the chemical-thermal energy generated in the combustion chamber into kinetic energy. The nozzle converts the low velocity, high pressure, high temperature gas in the combustion chamber into high velocity gas of lower pressure and temperature. Swedish engineer of French descent who, in trying to develop a more efficient steam engine, designed a turbine that was turned by jets of steam. The critical component – the one in which heat energy of the hot high-pressure steam from the boiler was converted into kinetic energy – was the nozzle from which the jet blew onto the wheel. De Laval found that the most efficient conversion occurred when the nozzle first narrowed, increasing the speed of the jet to the speed of sound, and then expanded again. Above the speed of sound (but not below it) this expansion caused a further increase in the speed of the jet and led to a very efficient conversion of heat energy to motion. The theory of air resistance was first proposed by Sir Isaac Newton in 1726. According to him, an aerodynamic force depends on the density and velocity of the fluid, and the shape and the size of the displacing object. Newton?s theory was soon followed by other theoretical solution of fluid motion problems. All these were restricted to flow under idealized conditions, i.e. air was assumed to posses constant density and to move in response to pressure and inertia. Nowadays steam turbines are the preferred power source of electric power stations and large ships, although they usually have a different design-to make best use of the fast steam jet, de Laval?s turbine had to run at an impractically high speed. But for rockets the de Laval nozzle was just what was needed.

Computational Fluid Dynamics (CFD) is an engineering tool that assists experimentation. Its scope is not limited to fluid dynamics; CFD could be applied to any process which involves transport phenomena with it. To solve an engineering problem we can make use of various methods like the analytical method, experimental methods using prototypes. The analytical method is very complicated and difficult. The experimental methods are very costly. If any errors in the design were detected during the prototype testing, another prototype is to be made clarifying all the errors and again tested. This is a time-consuming as well as a cost-consuming process. The introduction of Computational Fluid Dynamics has overcome this difficulty as well as revolutionised the field of engineering. In CFD a problem is simulated in software and the transport equations associated with the problem is mathematically solved with computer assistance. Thus we would be able to predict the results of a problem before experimentation. The current work aims at determining an optimum divergent angle for the nozzle which would give the maximum outlet velocity and meet the thrust requirements. Flow instabilities might be created inside the nozzle due to the formation if shocks which reduce the exit mach number as well as thrust of the engine. This could be eliminated by varying the divergent angle. Here analysis has been conducted on nozzles with divergent angles Experimentation using the prototypes of each divergent angle is a costly as well as a time consuming process. CFD proves to be an efficient tool to overcome these limitations. Here in this work the trend of various flow parameters are also analysed.

Computational Fluid Dynamics (CFD) is an engineering tool that assists experimentation. Its scope is not limited to fluid dynamics; CFD could be applied to any process which involves transport phenomena with it. To solve an engineering problem we can make use of various methods like the analytical method, experimental methods using prototypes. The analytical method is very complicated and difficult. The experimental methods are very costly. If any errors in the design were detected during the prototype testing, another prototype is to be made clarifying all the errors and again tested. This is a time-consuming as well as a cost-consuming process. The introduction of Computational Fluid Dynamics has overcome this difficulty as well as revolutionized the field of engineering. In CFD a problem is simulated in software and the transport equations associated with the problem is mathematically solved with computer assistance. Thus we would be able to predict the results of a problem before experimentation. The current work aims at determining an optimum divergent angle for the nozzle which would give the maximum outlet velocity and meet the thrust requirements. Flow instabilities might be created inside the nozzle due to the formation if shocks which reduce the exit mach number as well as thrust of the engine. This could be eliminated by varying the divergent angle. Here analysis has been conducted on nozzles with divergent angles Experimentation using the prototypes of each divergent angle is a costly as well as a time consuming process. CFD proves to be an efficient tool to overcome these limitations. Here in this work the trend of various flow parameters are also analyzed.

The modern research considering computational fluid dynamics is that it involves software testing and no prototype is need to build during designing stages and hence solution can be obtained faster and at less cost. Computational Fluid Dynamics become a popular tool for solving various problems and the physical aspects are governed by three aspects.

• Mass is conserved.

• Newton’s Second law is observed.

• Energy is conserved.

These factors are expressed in terms of the equation which is either integrals or differential equations. CFD is the art of study of replacing theses integrals or differential equations in terms of discredited algebraic forms which in turn are solved to obtain a number for flow field’s values at the discrete point in time or space. The final product of the study of CFD is a collection of the numbers in contrast to closed form analytic solution which is applicable in the practical solution. Flows and related phenomenon can be described by the partial differential equation, which cannot be solved analytically except in some special cases. To obtain the approximate solution, we have to use a Discretization technique which approximated the differential equation that can be later be solved by computer. The present work goes for deciding an ideal focalized point approached rocket engine nozzle used in a rocket Engine. The acceleration of the combustion gases from exit nozzle at hypersonic velocities is considered by COMSOL software. This CFD specialized beta CAE software system presents in detail all the steps taken to read a CAD file of a geometry simplification, in order to create a good quality shell mesh, Improve the mesh by manually optimizing the shape of the Macro Area and Disparate edge and throat span of the nozzle, which would give the most extreme outlet acoustic flow speed and meet the push prerequisites. This could be disposed of by various the divergent edges. Here investigation has been directed on the nozzle with disparate points with angles.

The nozzle is used to convert the chemical-thermal energy generated in the combustion chamber into kinetic energy. The nozzle converts the low velocity, high pressure, high temperature gas in the combustion chamber into high velocity gas of lower pressure and temperature.

The inlet Mach number is less than one, Convergent section accelerates it to sonic velocity at the throat and further accelerated to supersonic velocities by the diverging section.

Figure 1 – Convergent-divergent nozzle

In this project the designing and analysis of CD nozzle geometry is done in the CFD (Computational Fluid Dynamics software). Firstly the design of nozzle is made in Gambit software and then the nozzle geometry is further analyzed in fluent software in order to analyze the flow inside the CD nozzle and to get the view of the behavior of fluid inside the convergent-divergent section of nozzle.

A multidisciplinary analytic model of a aerospike rocket nozzle has been developed, this model includes predictions of nozzle thrust, nozzle weight, and effective vehicle gross-liftoff weight (GLOW). The linear aerospike rocket engine is the propulsion system proposed for the X-

2 The model has been developed to demonstrate multidisciplinary design optimization (MDO) capabilities for relevant engine concepts, assess performance of various MDO approaches, and provide a guide for future application development1.

Fluid–structure interaction (FSI) is the interaction of some movable or deformable structure with an internal or surrounding fluid flow. Fluid–structure interaction problems and multiphysics problems in general are often too complex to solve analytically and so they have to be analyzed by means of experiments or numerical simulation. Research in the fields of computational fluid dynamics and computational structural dynamics is still ongoing but the maturity of these fields enables numerical simulation of fluid-structure interaction. There are Two main approaches exist for the simulation of fluid– structure interaction problems:

II. Monolithic approach: In monolithic approach consisting the equations, governing the flow and the displacement of the structure are solved simultaneously, with a single solver. This approach becomes complicated but requires less time.

JJ. Partitioned approach: the equations governing the flow and the displacement of the structure are solved separately, with two distinct solvers. We shall used partitioned approach where fluid dynamic equations are solved using separate solver i.e. CFD and structural equations are solved using Finite element method in ANSYS. For industrial designing purpose this methodology is more reliable than the monolithic approach as design criteria for flow design and structural design is satisfied individually but it takes more time.

There are many parameters including rocket, such as thrust chamber assemble, thrust chamber injector, oxidizer zone, Gimbal bearing, thrust chamber body, Thrust chamber nozzle extension, nozzle, hypergol cartridge, etc lots of parameters are included there. But till we will study on aerospike nozzle, because our aim is to getting higher thrust. Therefore we had selected nozzle as the main parameter for this work. The thrust chamber nozzle extension increases the expansion ratio of the thrust chamber from 10:1 to 16:1. It is detachable unit that is bolted to the exit end ring of the thrust chamber. The interior of the nozzle extension is protected from the engine exhaust gas environmental by film cooling, using turbine exhaust gases as the coolant. The gases enter the

1.2. Project Objective

The objectives of this project are:

1. To obtain the optimized throat radius for nine different convergent and divergent angles in a rocket engine nozzle using CFD.

2. To get the optimal Mach number of nozzle by applying the optimized throat radius for two different static pressures using CFD.

3. To compare the optimal Mach number with numerically and experimentally.