Velocity triangles example velocity triangles example april 12, 2012 mechanical and aerospace engineering department 2. Velocity triangle for degree of reaction 12 in a turbine this reduces the tendency of boundary layer separation from the blade surface avoiding large stagnation pressure losses. V f1 is the velocity of flow at entrance, so it is perpendicular to the direction of blades motion and it does not any work, but this is the component which is fully responsible for flow of steam through the turbine. Reaction occurs when the water is accelerated or decelerated over the vanes. Variation in the shape of the velocity triangles with radius the desired radial variation in degree of reaction rr and enthalpy change dh or i. What is the difference in velocity triangles of impulse. In reaction turbine fixed blade angle is equal to blade exit angle i. Hence for a zero reaction impulse turbine flow angle at the exit of the blade will be the same as that at the inlet.
Zweifel investigated the ratio of the tangential force f t to an idealised tangential force f tid and found a common value of. State briefly the reasons for fitting a draft tube to a reaction turbine and sketch three common types. The inlet pipe is axial, and fluid enters the eye, that is the center of the impeller with little, if any, whirl component of velocity. That is, the blade pushes and turns the fluid in the direction of the blade motion, thereby doing work on the fluid. In this article, we are going to discuss the hydraulic turbine along with its definition, classification, advantages. In an impulse turbine, the degree of reaction is zero, meaning that the gas expands and accelerates as it turns in the stator passages, and then is merely redirected at constant thermodynamic state by the moving rotor blades. In reaction turbines, the pressure of the steam is reduced as it moves over the moving blades that gives rise to an increase in kinetic energy. Assuming the velocity of flow as constant and equal to 2. The velocity diagram will show clear symmetry in the relative frame. The fixed blade angles of the two reaction turbines equal to the given inlet angle. A triangle used in the analysis of turbomachinery to determine the velocity w of the working fluid relative to a rotor, usually at the inlet or outlet of a stage. The absolute component of velocity will be denoted by, c. The velocity vector diagram at inlet and out of the runner of a francis turbine is shown in fig.
Each stage consists of a nozzle and blade row where the kinetic energy of the jet is absorbed into the turbine rotor as useful work. Axial turbine stage comprises a row of fixed guide vanes or nozzles often called a stator row and a row of moving blades or buckets a rotor row. In this turbine, the work is broken down into various stages. Velocity triangle for moving blade of an impulse turbine slideshare. Classification, single stage impulse turbine, condition for maximum blade efficiency, stage efficiency, need and methods of compounding, multistage impulse turbine, expression for. Considering the exit discharge as radial, determine the a the peripheral velocity at inlet, and b blade angle at outlet. An axial turbine has a similar construction as an axial compressor, but it operates in the reverse, converting flow of the fluid into rotating mechanical energy a set of static guide vanes or nozzle vanes. Gas with an absolute velocity c 1 making an angle a 1, angle measured from the axial direction enters the nozzle in impulse turbine or stator blades in reaction turbine. The optimum rotational speed of the turbine was in. May 26, 2015 note that a singlestage turbine can also satisfy these conditions for a repeating stage. Reaction turbine parsonss turbine, condition for maximum utilization factor, reaction staging. In the diagram for a reaction turbine, the sides of the triangle represent.
Velocity triangle for moving blades of a reaction turbine let vb liner velocity of the moving bladeba v absolute velocity of steam entering the moving bladebc, vr relative velocity of. You will also draw the blade pro les for the rotor ans stator stator and rotor. For r 1, the utilization factor does not reach unity but reaches some maximum finite value. The axial flow turbine can be classified as 1 impulse and 2 reaction.
The impulse turbine is a reaction turbine with a degree of reaction of zero r 0. The picture shows combined velocity triangle of steam turbine. Changes in the flow direction and velocity are easy to understand with the help of the velocity triangles. In steam turbines, enthalpy of the steam is first converted into kinetic energy in nozzlesblade passage. Velocity triangle for degree of reaction 12 in a turbine. The stationary blades are designed in such a fashion that the passages between them form the flow areas of nozzles, so they become nozzles with full steam admission around the rotor periphery. Francis turbine velocity triangles, design parameters, runner.
In pure reaction turbines, the last two terms only will be present. In this video, i explained velocity triangle and work done of francis turbine with animation and following topic. Velocity triangle for moving blade of an impulse turbine. Figure 3 velocity triangle v1, v2 absolute velocities at inlet and outlet. Velocity triangles are used to illustrate the flow in the bladings of turbo machinery. The fixed blades act as nozzles and accelerate the steam to a moderate velocity due to the partial pressure drop. Impulse and reaction turbines turbines machines fluid. Table 1 axial flow compressor characteristics type of application type of flow inlet relative velocity mach number pressure ratio per stage ef. If the rotor discharge velocity is axial, the turbine operates in the so called maximum utilization regime, and c u3 0 and w u3 u, therefore 2 2.
The francis turbine is a mixed flow reaction turbine. The moving blades of impulse turbines do not have a change in flow area. What is the difference in velocity triangles of impulse and. Steam turbines, turbine blades, velocity diagrams, impulse, reaction. According to the newtons second law of motion,the direction of force in the blades, work done in the direction of motion of the blades, mathematically, axial thrust on the wheel is the velocity difference between inlet and outlet steams flow. Mechanical and aerospace engineering department florida institute of technology. The stage velocity triangles are shown in fig 1, which also includes the case of a 50% reaction turbine for comparison. In the last lecture we discussed the basic mechanisms of energy exchange in compressors and drew some simple velocity triangles to show how we go from the stationary coordinate system to one in the moving blades. The 2nd and 3rd stage of the turbine are 50 % reaction stages. Francis turbine diagram, working, parts, advantages.
In most designs, the reaction of the turbine varies from hub to shroud. In reaction turbines, the pressure of the steam is reduced as it moves over the moving blades that gives rise to an increase in. Compressor velocity triangles ut aerospace engineering. Velocity triangles for turbine and compressor design. It has three stages, each composed of a row of fixed blades and row of moving blades. This reduces the tendency of boundary layer separation from the blade surface avoiding large stagnation pressure losses. Types and classification, equation for velocity and mass flow rate.
Impulse turbine efficiency calculation methods with organic. Velocity triangles are used to illustrate flow conditions. The inlet velocity triangle the outlet velocity triangle at the inlet there is no component of absolute velocity in the direction of rotation. Francis turbines are probably used most extensively because of their wider range of suitable heads, characteristically from three to 600 metres. Francis turbine is a mixed flow reaction turbine in which water enters radially and leaves axially at its center. Francis turbinevelocity triangleanimation,work done. Velocity triangles elementary analysis of axial compressors begins with velocity triangles. Stages satisfying these requirements are often referred to as normal stages.
Pelton turbine velocity triangles, design parameters, maximum efficiency. Turbomachine notes 15me53 turbo machines subject code. Let us draw a diagram of the steam turbine velocity. Fluid enters the stator with absolute velocity c 1 at angle. The analysis will be carried out at the mean height of the blade, where the peripheral velocity or the blade speed is, u. At the highhead range, the flow rate and the output must be large. For 50 % reaction turbine, the velocity diagram is symmetric i. The stage loading coefficient of the zero reaction turbine. Here v w1 denotes the velocity of whirl at entry of moving blades and since it is the same direction of the motion of moving blades so it is the actual component which does work on blades. As a result of pressure decrease in the moving blade, a reaction force will be produced. At the lowhead end, propeller turbines are usually more efficient unless. If the vane is smooth then vr1 vr2, and k 1 8 note. Velocity diagrams and analysis of impulse and reaction turbines. The high velocity steam impinges on the curved blades which change the flow direction of steam.
They do not therefore change the velocity of the steam but only change its direction. The 2nd and 3rd stage of the turbine are 50 % reaction. Ame415 fall 2020 lecture 3 page 14 means that at the same speed of rotation u and same nozzle discharge angle. Vu1, vu2 tangential component of absolute velocities at inlet and outlet. Another impulse turbine is the pressure compound or ratteau turbine. Turbines are subdivided into impulse and reaction machines.
The air that leaves the moving blades enters the next set of nozzles where the enthalpy decreases further, and the velocity is. That is, the blade pushes and turns the fluid in the direction of the blade motion, thereby doing. Fundamentals of fluid mechanics chapter 12 pumps and turbines. The three velocity vectors namely, blade speed, absolute velocity and relative velocity in relation to the rotor are used to form a triangle called velocity triangle.
Mathematical model the following figure 5 is an enthalpyentropy diagram mollier diagram 3 of the expansion process for a radial turbine with a diffuser where 1, 2, 3 and 4 represent the entry to the stator, entry to the rotor, exit from the rotor and exit. On this channel you can get education and knowledge for general issues and topics. Reaction for axial discharge velocity if we impose zero exit velocity at the rotor discharge, there is a. Design point totaltototal efficiency and deflection angle contours for a turbine stage of 50 percent reaction. One tangential component v w1 and another axial component v f1. In reaction turbines, the rotor inlet pressure is higher than the outlet pressure. The flow is uniform along the circumference and is steady. In impulse reaction turbines of radial flow type, all the terms will be present. Jan 18, 2018 now let us draw the velocity triangles at inlet and outlet tips of the moving blade as shown in fig. The velocity diagram of a reaction stage is symmetrical as is evident from figure 6. In it the steam from the boiler, under a high pressure and temperature, is distributed around the fixed bladesguide mechanism. All the blades are symmetrical in impulse turbine i. For this type of turbine, several useful relationships can be derived relating the shapes of the velocity triangles to the flow coefficient, stage loading, and reaction parameters.
A force is needed to do this and the reaction to this force acts on the vanes. An axial turbine is a turbine in which the flow of the working fluid is parallel to the shaft, as opposed to radial turbines, where the fluid runs around a shaft, as in a watermill. Reaction turbine reaction turbines are invited by c. Rishi raj design of an impulse turbine blades hasan2. Actual velocity triangle of francis turbine by anupamiit, cc bysa 3. The change in flow direction of steam causes a force to be. The details of the airfoil shape require aerodynamic. Where v1, v2 absolute velocity of fluid at inlet and outlet. Impulse turbine began employing reaction of upto 20% at the root of the moving blades in order to counteract the poor efficiency incurred from zero or even negative reaction. The utilization factor for a fixed nozzle angle will increase as the reaction approaches 100%. It also should be remembered that the gas turbine axial flow compressor consumes between 55%65% of the power produced by the turbine section of the gas turbine. Turbine velocity triangles ced, cecos university, peshawar.
The velocity triangles in this case are shown in figure 4. An axial turbine has a similar construction as an axial compressor, but it operates in the reverse, converting flow of the fluid into rotating mechanical energy. Steam turbine is widely use as a prime mover in power plants, refineries, petrochemical plants, food processing plants etc. Velocity triangles the three velocity vectors namely, blade speed, absolute velocity and relative velocity in relation to the rotor are used to form a triangle called velocity triangle. High velocity jet from nozzles produce an impulse on the moving blade and jet coming out from still higher velocity from moving blades produces a reaction. Theory of turbo machinery turbomaskinernas teori chapter 4. This turbine is used for medium heads with medium discharge. Impulsive and reaction forces are determined by examining the changes in velocity magnitude and direction when the water.
The runner of this turbine essentially consists of a set of curved blades mounted symmetrically in the runner wheel. Turbine exercice draw the velocity triangles for a full periodic turbine stage. In a vertical francis turbine, the runner speed is 380 r. Kaplan turbine used when load on turbine remains constant. Rishi raj design of an impulse turbine blades hasan1. The shape of the moving blades however is not the same for impulse and reaction turbines.
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