Lect- 35 - NPTELnptel.ac.in/courses/101101058/downloads/Lec-35ppts.pdf · developed the radial...
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1 Lect- 35
Transcript of Lect- 35 - NPTELnptel.ac.in/courses/101101058/downloads/Lec-35ppts.pdf · developed the radial...
1
Lect- 35
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 2
Lect-35
In this lecture...
• Radial flow turbines• Types of radial flow turbines• Thermodynamics and aerodynamics• Losses in radial flow turbines
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 3
Lect-35
Radial turbines
• Development of radial flow turbines dates back to 1830’s by Fourneyron, who developed the radial outflow type turbine.
• Later on Francis and Boyden developed the radial inflow type turbine.
• The inward-flow radial (IFR) turbine covers tremendous ranges of power, rates of mass flow and rotational speeds.
• IFR turbines are used in a variety of applications ranging from hydroelectric power plants to small gas turbines.
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 4
Lect-35
Radial turbines• There are two types of inward flow radial
turbines• Cantilever turbine• 90o IFR turbine
• Cantilever turbine• Similar to the impulse type turbine • Little change in relative velocity across the rotor• Aerodynamically very similar to the axial impulse
turbine• Can be designed in a similar manner as axial
turbines.
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 5
Lect-35
Radial turbines
Nozzle blades
Rotor blades
Flow
12
3
C2 V2
U2
V3
U3
Ca3
Cantilever turbine arrangement and velocity triangles
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 6
Lect-35
Radial turbines• 90o IFR turbine
• This turbine has a striking similarity with a centrifugal compressor.
• The flow direction and blade motion are reversed.
• The flow enters the turbine radially and exits the turbine axially.
• Straight radial blades are generally preferred as curved blades would incur additional stresses.
• The rotor or impeller ends with an exducer. • Usually the flow exiting the rotor passes through
a diffuser to recover KE, which would otherwise be wasted.
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 7
Lect-35
Radial turbines
Nozzle blades
Rotor blades
Flow
1
2
3Diffuser
4
Volute/Scroll
C2 V2
U2
V3
U3
Ca3
α2 β3
90o IFR turbine arrangement and velocity triangles
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 8
Lect-35
Thermodynamics of radial turbines
• We shall consider a 90o IFR turbine. • Components include: nozzle, radial bladed
rotor and diffuser.• We shall assume complete adiabatic
expansion in the turbine.• Frictional processes cause the entropy to
increase in all the components.• There is no change in stagnation
enthalpy/temperature across the nozzle and the diffuser.
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 9
Lect-35
Thermodynamics of radial turbines
s
T01
203
1
3
P02
P3
P2
P01
P1
pcV2
22
T-s diagram for an IFR turbine
pcC2
23
T01=T02
P4
4
P03 P04
02
02rel
2
22U
T03=T04
3ss3s
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 10
Lect-35
Radial turbines
Nozzle blades
Rotor blades
Flow
1
2
3Diffuser
4
Volute/Scroll
C2 V2
U2
V3
U3
Ca3
α2 β3
90o IFR turbine arrangement and velocity triangles
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 11
Lect-35
Thermodynamics of radial turbines
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 12
Lect-35
Thermodynamics of radial turbines
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 13
Lect-35
Thermodynamics of radial turbines
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 14
Lect-35
Thermodynamics of radial turbines
• Nominal design• Defined by a relative flow of zero
incidence at the rotor inlet (V2=Cr2).• An absolute flow at the rotor exit that is
axial (C3=Ca3). • Therefore, with Cw3=0 and Cw2=U2, the
specific work for nominal design is ∆W=U2
2 .
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 15
Lect-35
Thermodynamics of radial turbines
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 16
Lect-35
Thermodynamics of radial turbines
s
T01
203
1
3
P02
P3
P2
P01
P1
pcV2
22
T-s diagram for an IFR turbine
pcC2
23
T01=T02
P4
4
P03 P04
02
02rel
2
22U
T03=T04
3ss3s
03ss
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 17
Lect-35
Thermodynamics of radial turbines
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 18
Lect-35
Thermodynamics of radial turbines
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 19
Lect-35
Thermodynamics of radial turbines
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 20
Lect-35
Losses in radial turbines
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 21
Lect-35
Losses in radial turbines
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 22
Lect-35
Losses in radial turbines
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 23
Lect-35
Losses in radial turbines
• In general, losses in a IFR turbine can be classified as:• nozzle blade row boundary layers,• rotor passage boundary layers,• rotor blade tip clearance,• disc windage (on the back surface of the
rotor),• kinetic energy loss at exit.
• The above sources of losses are of significance for determining the optimum design geometry.
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 24
Lect-35
Losses in radial turbines
• Incidence losses• At off-design conditions, the fluid is likely to
enter the rotor at a relative flow angle different from the optimum angle.
• This leads to an additional loss component due to incidence angles.
• Often defined as equal to the kinetic energy corresponding to the component of velocity normal to the rotor vane at inlet.
• There is an increase in entropy and hence a corresponding loss in enthalpy due to incidence.
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 25
Lect-35
Losses in radial turbines
s
T01
203
1
3
P02
P3
P2
P01
P1
pcV2
22
T-s diagram for an IFR turbine
pcC2
23
P4
4
P03 P04
02
02rel
2
22U
3ss3s
V2 β2, opt
V’2
β2
2: after entry to rotor
1: before entry to rotor
Prof. Bhaskar Roy, Prof. A M Pradeep, Department of Aerospace, IIT Bombay 26
Lect-35
In this lecture...
• Radial flow turbines• Types of radial flow turbines• Thermodynamics and aerodynamics• Losses in radial flow turbines
