Selection of Stator-Rotor Combinations
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Transcript of Selection of Stator-Rotor Combinations
Selection of Stator-Rotor Combinations
How to Execute Conservation of Rothalpy ??Enthalpy
Kinetic Energy
Velocity Vector Field
Fluid Dynamics
Generation of Change in rate of angular momentum
(An Action)
Who Will take the Reaction ???
Shaft Torque is the final need as
Reaction
Basic Rules for Design of An Ideal Turbine Flow Path
• Created highest usable form of a resource.• Creation of initial velocity/kinetic energy using Stator.• X1 (Impulse)+X2(Reaction)+(1-X1-X2)(centripetal)
• Y1 (Radial)+(1-Y1 )(Axial)• Design of Flow Path using Conservation of rothalpy.• Design blade cascade using conservation of mass and
momentum.• A design of an Ideal Machine …..• Each stage can do finite amount of action….!!!• Many stages are needed to complete the action….
Flow in Stator-Rotor Inter stage Gaps
Geometrical Details along the Third Direction
• True flow through a turbo-machinery is three-dimensional. • Flow and tangential flow velocities are very important for
better operation of a turbo-machine.• The third component, which is normal to flow and
tangential directions is in general of no use.• This direction can better represented as blade height
direction.
Third Direction of an Axial Flow Turbo-Machines
• The third direction in an axial flow machine is the radial direction.
• The direction of Centrifugal forces!• Strong centrifugal forces are exerted on blades & fluid in
radial direction. • The centrifugal field distorts the flow velocity profiles
considerably.• Fluid particles tend to move outwards rather than passing
along cylindrical stream surfaces as classically assumed.
• Particularly in tall blade (low hub: tip) ratio designs.• An approach known as the radial equilibrium method,
widely used for three-dimensional design calculations in a an axial flow machine.
Radial Equilibrium Theory of Turbo-machines
P M V SubbaraoProfessor
Mechanical Engineering Department
A Model for Stable Operation of A Machine
A guiding equation for distribution of load along blade length ….
Radial Variation of Blade Geometry
Radial Equilibrium Theory
• Assumes that flow is in radial equilibrium before and after a blade row.
• Radial adjustment takes place through the row.• More important for Axial Flow Machines.
Radial Equilibrium Analysis
The centrifugal force = (rdrd)2r V = r
The centrifugal force is
The pressure force on the element
drdVF lcentrifuga2
rdpdFpressure
If the two forces are the only ones acting (viscous and other effects neglected), the particle will move at constant radius if:
lcentrifugapressure FF
rdrVdp 2
drdVrdpd 2
Equilibrium Condition for A Rotating Fluid
A mechanical equilibrium of a fluid elements demands thermodynamic equilibrium.The fluid must be facilitated to adjust radially as per the requirements.This process of radial adjustment of fluid parcels is well assumed to be isentropic.
0dpdhvdpdhTds
dpdh
rdrVdh 2
The radial variation of whirl velocity should be according to above equation.
How to implement on a machine?
rdrVdp 2
2222
2222
0VVV
hV
hh rf
0222
222
0
VVV
hddh rf
Implementation of Radial Equilibrium
Stagnation enthalpy should conserve, as there are not interactions with rotor at inlet or exit.
rdrVdh 2
0222
2222
0
VVV
drdrVdh rf
0222
22220
VVV
drd
rV
drdh rf
02
0 dr
dVVdr
dVVdr
dVV
rV
drdh r
rf
f
Radial component of velocity should be constant (zero) along radial direction for radial equilibrium of flow.
02
0 dr
dVVdr
dVV
rV
drdh f
f
Constant in a turbo-machine along meridoinal Plane
021 2
drrVd
rV
drdV f
Stagnation enthalpy is Constant in a turbo-machine along radial direction at intake and discharge.
Constant21: 22
,2 bladerelx UVVhIRothalpy
Twisted Blades for Large Turbines
021 2
drrVd
rV
drdV f