International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 08 Issue: 08 | Aug 2021 www.irjet.net p-ISSN: 2395-0072 © 2021, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page 4167 Modelling and Analysis of a Convergent – Divergent Nozzle Fareen Nizami 1 , Dr. Basawaraj 2 , Sanjeev G Palekar 3 , Prashant Channaveere 4 1 P.G. Student, Department of Aerospace Propulsion Technology, Visvesvaraya Technological University-Centre for Post Graduate Studies, Bengaluru Region, VIAT, Muddenahalli, Chickballapur, Karnataka, India 2 Associate Professor& Chairman, Department of Aerospace Propulsion Technology, Visvesvaraya Technological University-Centre for Post Graduate Studies, Bengaluru Region, VIAT, Muddenahalli, Chickballapur, Karnataka, India 3 Assistant Professor, Department of Aerospace Propulsion Technology, Visvesvaraya Technological University- Centre for Post Graduate Studies, Bengaluru Region, VIAT, Muddenahalli, Chickballapur, Karnataka, India 4 Assistant Professor, Department of Aeronautical Engineering, East West College of Engineering, Yelahanka New Town, Bangalore, Karnataka, India. ---------------------------------------------------------------------***---------------------------------------------------------------------- Abstract - Nozzle is a part of the propulsion system which is used to accelerate the hot gases flowing through it. The nozzle geometry is highly important because it directly affect the overall performance of propulsion system. Also, design of nozzle is an important aspect for achieving the maximum Mach number or supersonic speed. To achieve supersonic speed a type of nozzle called Convergent - Divergent nozzle or otherwise known as the de Laval nozzle or CD nozzle is used which converts the high temperature, high pressure, and low velocity gas into high velocity and low pressure gas at the exit. The main aim of this work is to model Convergent – Divergent nozzle and analyse the variation in flow parameters that are static pressure, velocity, static temperature and Mach number by modifying the nozzle divergent angle, keeping same throat and inlet diameter and by using the optimum convergent angle of 28.5°. Analysis is carried out for divergent angles 5°, 10°, 15° and 20° using computational fluid dynamics software(CFD). CFD results were compared with the theoretical results. Variation in flow parameters at the nozzle outlet is studied so as to find the optimum divergent angle for the optimum convergent angle. By considering the results of all the divergent angles 20° gave maximum Mach number that will lead to improve performance of the nozzle and thereby the power and efficiency of a propulsion system. Key Words: Convergent – Divergent nozzle, Divergent angle, Convergent angle, CFD analysis, ANSYS Fluent 1.INTRODUCTION Nozzle is a very essential component of the propulsion system whose function is to accelerate the hot gases flowing through it. It controls the rate of flow, direction and pressure. It also converts pressure energy into kinetic energy. The performance of nozzle greatly affects the efficiency of propulsion system. Generally, there are different types of nozzles. Convergent – Divergent nozzle are among the one which are in great demand in order to achieve supersonic speeds, required in various fields of engineering. The Convergent-Divergent or CD nozzle is used in rocket engines, supersonic jet engines and in some steam turbines. It is also known as the de-Laval nozzle. The gas passing through a CD nozzle is isentropic and adiabatic in nature. From Figure 1 we can see that first the flow is subsonic. This happens at the convergent section of the nozzle followed by the throat where the area is the smallest and the Mach number is 1. Here the flow becomes sonic in nature. This phenomenon is called “Choked Flow”. Next as the gas passes through the divergent section, the nozzle cross-sectional area increases. The gas undergoes expansion and reaches supersonic velocity. The performance of this nozzle depends upon the flow parameters which are affected by the geometry of the nozzle. Fig -1: Convergent-Divergent nozzle Many researchers have worked to obtain an optimum geometry of the Convergent – Divergent nozzle. Karna S. Patel [1] has modelled different geometries of a Convergent - Divergent nozzle with 5°, 10° and 15° divergent angle have undergone analysis using computational fluid dynamics software (CFD), in which 15° geometry gave the efficient results. Biju Kuttan P et al., [2] have carried out work to analyse the variations of flow parameters like the static pressure, Mach number, turbulent intensity by taking 4°, 7°, 10°, 13° and 15° as divergent angles were 15° was considered the good nozzle design. I. Mir et al., [3] have carried out analysis on different geometrical configurations of a Convergent - Divergent nozzle by varying convergent section length from 602 mm to 655 mm and convergent angle from 28° to 30°, the geometry with 640 mm convergent length and 28.5° convergent angle was giving the maximum thrust. B.V.V. Naga Sudhakar et al., [4] have