INTERNATIONAL JOURNAL OF PROFESSIONAL ENGINEERING STUDIES Volume 9 /Issue 2 / SEP 2017 DESIGN AND CFD ANALYSIS OF CONVERGENT AND DIVERGENT NOZZLE 1P.VINOD KUMAR,2B.KISHORE KUMAR 1 PG Scholar, Department ofMECH,NALANDA INSTITUTION OF ENGINEERING AND TECHNOLOGY KantepudiSattenapalli, GUNTUR,A.P, India, Pin: 522438 2 Assistant Professor, Department of MECH,NALANDA INSTITUTION OF ENGINEERING AND TECHNOLOGY,Kantepudi,Sattenapalli, GUNTUR,A.P, India, Pin: 522438 Abstract narrowed, increasing the speed of the jet to the speed Nozzle is a device designed to control the of sound, and then expanded again. Above the speed rate of flow, speed, direction, mass, shape, and/or the of sound (but not below it) this expansion caused a pressure of the Fluid that exhaust from them. further increase in the speed of the jet and led to a Convergent-divergent nozzle is the most commonly very efficient conversion of heat energy to motion. used nozzle since in using it the propellant can be The theory of air resistance was first proposed by Sir heated incombustion chamber. In this project we Isaac Newton in 1726. According to him, an designed a new Tri-nozzle to increase the velocity of aerodynamic force depends on the density and fluids flowing through it. It is designed based on velocity of the fluid, and the shape and the size of the basic convergent-Divergent nozzle to have same displacing object. Newton’s theory was soon throat area, length, convergent angle and divergent followed by other theoretical solution of fluid motion angle as single nozzle. But the design of Tri-nozzle is problems. All these were restricted to flow under optimized to have high expansion co-efficient than idealized conditions, i.e. air was assumed to posses single nozzle without altering the divergent angle. In constant density and to move in response to pressure the present paper, flow through theTri-nozzle and and inertia. Nowadays steam turbines are the convergent divergent nozzle study is carried out by preferredpower source of electric power stations and using SOLID WORKS PREMIUM 2014.The nozzle large ships, although they usually have a different geometry modeling and mesh generation has been design-to make best use of the fast steam jet, de done using SOLID WORKS CFD Software. Laval’s turbine had to run at an impractically high Computational results are in goodacceptance with the speed. But for rockets the de Laval nozzle was just experimental results taken from the literature. what was needed. 1. Introduction to nozzle A nozzle is a device designed to control the direction or characteristics of a fluid flow (especially Swedish engineer of French descent who, in trying to to increase velocity) as it exits (or enters) an enclosed develop a more efficient steam engine, designed a chamber. A nozzle is often a pipe or tube of varying turbine that was turned by jets of steam. The critical cross sectional area and it can be used to direct or component – the one in which heat energy of the hot modify the flow of a fluid (liquid or gas). Nozzles are high-pressure steam from the boiler was converted frequently used to control the rate of flow, speed, into kinetic energy – was the nozzle from which the direction, mass, shape, and/or the pressure of the jet blew onto the wheel. De Laval found that the most stream that emerges from them. A jet exhaust efficient conversion occurred when the nozzle first produces a net thrust from the energy obtained from IJPRES INTERNATIONAL JOURNAL OF PROFESSIONAL ENGINEERING STUDIES Volume 9 /Issue 2 / SEP 2017 combusting fuel which is added to the inducted air. gases is directly backwards, as any sideways This hot air is passed through a high speed nozzle, a component would not contribute to thrust. propelling nozzle which enormously increases its 2. Literature review kinetic energy. The goal of nozzle is to increase the CONVERGENT-DIVERGENT nozzle is kinetic energy of the flowing medium at the expense designed for attaining speeds that are greater than of its pressure and internal energy. Nozzles can be speed of sound. the design of this nozzle came from described as convergent (narrowing down from a the area-velocity relation (dA/dV)=-(A/V)(1-M^2) M wide diameter to a smaller diameter in the direction is the Mach number ( which means ratio of local of the flow) or divergent (expanding from a smaller speed of flow to the local speed of sound) A is area diameter to a larger one). A de Laval nozzle has a and V is velocity The following information can be convergent section followed by a divergent section derived from the area-velocity relation – and is often called a convergent-divergent nozzle 1. For incompressible flow limit, i.e. for M tends to ("con-di nozzle"). Convergent nozzles accelerate zero, AV = constant. This is the famous volume subsonic fluids. If the nozzle pressure ratio is high conservation equation or continuity equation for enough the flow will reach sonic velocity at the incompressible flow. narrowest point (i.e. the nozzle throat). In this 2. For M < 1, a decrease in area results in increase of situation, the nozzle is said to be choked. velocity and vice vera. Therefore, the velocity Increasing the nozzle pressure ratio further increases in a convergent duct and decreases in a will not increase the throat Mach number beyond Divergent duct. This result for compressible subsonic unity. Downstream (i.e. external to the nozzle) the flows is the same as that for incompressible flow. flow is free to expand to supersonic velocities. Note 3. For M > 1, an increase in area results in increases that the Mach 1 can be a very high speed for a hot of velocity and vice versa, i.e. the velocity increases gas; since the speed of sound varies as the square root in a divergent duct and decreases in a convergent of absolute temperature. Thus the speed reached at a duct. This is directly opposite to the behavior of nozzle throat can be far higher than the speed of subsonic flow in divergent and convergent ducts. sound at sea level. This fact is used extensively in 4. For M = 1, dA/A = 0, which implies that the rocketry where hypersonic flows are required, and location where the Mach number is unity, the area of where propellant mixtures are deliberately chosen to the passage is either minimum or maximum. We can further increase the sonic speed. Divergent nozzles easily show that the minimum in area is the only slow fluids, if the flow is subsonic, but accelerate physically realistic solution. sonic or supersonic fluids. Convergent-divergent One important point is that to attain supersonic nozzles can therefore accelerate fluids that have speeds we have to maintain favorable pressure ratios choked in the convergent section to supersonic across the nozzle. One example is attain just sonic speeds. This CD process is more efficient than speeds at the throat, pressure ratio to e maintained is allowing a convergent nozzle to expand (Pthroat / P inlet)=0.528. supersonically externally. The shape of the divergent section also ensures that the direction of the escaping IJPRES INTERNATIONAL JOURNAL OF PROFESSIONAL ENGINEERING STUDIES Volume 9 /Issue 2 / SEP 2017 Table1: speeds vs mach number 3.1 Conical Nozzles Reg Subs Trans So Super Hyper High- ime onic onic nic sonic sonic hyper Ma <1.0 0.8- 1.0 1.0- 5.0- sonic ch 1.2 5.0 10.0 >10.0 From table.1 at transonic speeds, the flow field around the object includes both sub- and supersonic Fig3.1 conical nozzles parts. The transonic period begins when first zones of 1. Used in early rocket applications because of M>1 flow appear around the object. In case of an simplicity and ease of construction. airfoil (such as an aircraft's wing), this typically 2. Cone gets its name from the fact that the walls happens above the wing. Supersonic flow can diverge at a constant angle decelerate back to subsonic only in a normal shock; 3. A small angle produces greater thrust, because it this typically happens before the trailing edge. (Fig.a) maximizes the axial component of exit velocity and As the speed increases, the zone of M>1 flow produces a high specific impulse increases towards both leading and trailing edges. As 4. Penalty is longer and heavier nozzle that is more M=1 is reached and passed, the normal shock reaches complex to build the trailing edge and becomes a weak oblique shock: 5. At the other extreme, size and weight are the flow decelerates over the shock, but remains minimized by a large nozzle wall angle – Large supersonic. A normal shock is created ahead of the angles reduce performance at low altitude because object, and the only subsonic zone in the flow field is high ambient pressure causes overexpansion and flow a small area around the object's leading edge separation The governing continuity, momentum, and energy 6. Primary Metric of Characterization: Divergence equations for this quasi one-dimensional, steady, Loss isentropic flow can be expressed, respectively 3.2 BELL and Dual Bell 3. Types of nozzles Types of nozzles are several types. They could be based on either speed or shape. a. Based on speed The basic types of nozzles can be differentiated as • Spray nozzles • Ramjet nozzles b. Based on shape The basic types of nozzles can be differentiated as Fig3.2 (1): BELL and Dual Bell • Conical This nozzle concept was studied at the Jet Propulsion • Bell Laboratory in 1949. In the late 1960s, Rocket dyne • Annular IJPRES INTERNATIONAL JOURNAL OF PROFESSIONAL ENGINEERING STUDIES Volume 9 /Issue 2 / SEP 2017 patented this nozzle concept, which has received 2.
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