1. Turbomachinery Class 12

2. Turbine
Compressor

3. Compressor
Turbine

5. Radial Inflow Turbines
Radial turbines largely used in power system applications
Primitive design, easy to fabricate
Capable of large per stage shaft work with low mass flow rate
Low sensitivity to tip clearance
Bulky / heavy

6. Low Cost Radial Compressor – Ex. 4, p. 83

7. Low Cost Radial Machines

8. Low Cost Radial Machines

9. Low Cost Turbine – Ex. 5 p. 85

10. Axial vs. Radial Machines
Need to determine what type of turbine is most efficient for application
- function of Ns for both compressors and turbine

11. Need to determine what type of turbine is most efficient for application
- function of Ns for both compressors and turbine

12. Radial Inflow [900 IFR] Turbines
Kinematic view
Thermodynamic view
Exit part of rotor (exducer) is curved to remove most of tangential component of velocity
Advantage of IFR turbine: efficiency equal to axial turbine, greater
amount of work per stage, ease of manufacture, ruggedness

13. Radial Flow Turbines
Radial Inflow Turbine with Scroll or Distributor

14. Radial Flow Turbines
Radial Inflow Turbine Stator/Rotor

15. Radial Flow Turbines
Radial Inflow Turbine Stator/Rotor [No shroud]

16. Radial Flow Turbines Radial Inflow Turbine Scroll
Scroll or distributor
- streamwise decreasing cross flow area
- provide nearly uniform properties at exit

17. Radial Flow Turbines

18. Radial Flow Turbines Scroll Design Principles
Mass balance rVr=constant
Free vortex rV=constant

19. Radial Flow Turbines
Radial Inflow Turbine Scroll - Stator

20. Radial Flow Turbines Radial Inflow Turbine Impeller Note
- direction of rotation
- rotor rearward curvature

21. Radial Flow Turbine Design
Nominal Stator / Rotor Design:
Station 1 – Inlet to Stator
Station 2 – Exit of Stator, Inlet to Rotor
[Radially inward]
Station 3 – Exit of Rotor
[Absolute velocity is axial]
Station 4 - Exit of Diffuser
Rotor inlet relative velocity is radially inward
- For Zero Incidence at Rotor Inlet, W2=Cr2 and Cq2=U2
Rotor exit absolute flow is axial
- For Axial Flow at Rotor Exit, C3=Cx3 and Cq3=0 C2
Cm2=Cr2=W2 U2
Cm3=C3=Cx3 U3 W3  

22. Radial Flow Turbine Design- 900 IFR
For adiabatic irreversible [friction] processes in rotating components
From the Alternate Euler Equation:
and

23. Radial Flow Turbine Design
substituting:
Thus from Alternate Euler’s Equation :

24. Specific Speed & Diameter Indicates Flowpath Shape

25. Specific Speed Indicates Flowpath Shape (Cordier Diagram)
From Logan
Ns is dimensionless
From Wright and Balje

26. Radial Flow Turbine Design
Example: Dixon 8.1
The rotor of an IFR turbine, designed to operate at nominal condition,
Diameter is cm and rotates at 38,140 rev/min.
At the design point the absolute flow angle at the rotor entry is 72 deg.
The rotor mean exit diameter is ½ the rotor diameter
The relative velocity at the rotor exit is twice the relative velocity at the inlet.

27. Radial Flow Turbine Design
Example: Dixon 8.1

28. Radial Flow Turbine Design
Example: Dixon 8.1

29. Radial Flow Turbine Design
Example: Baskharone p
0=inlet =stator exit =rotor inlet 3=rotor exit
Stator / nozzle exit Mach number M1=0.999

30. Radial Flow Turbine Design
Example: Baskharone p
0=inlet =stator exit =rotor inlet 3=rotor exit
Stator / nozzle exit Mach number M1=0.999

31. Radial Flow Turbine Design
Example: Baskharone p cont’d
In constant area interstage duct, apply free-vortex condition to flow from stator exit to rotor inlet

32. From Centrifugal Compressor Notes
Slip: flow does not leave impeller at metal angle [even for inviscid flow]
If absolute flow enters impeller with no swirl, =0.
If impeller has swirl (wheel speed) , relative to the impeller the flow has an angular velocity -  called the relative eddy [from Helmholtz theorem].
Effect of superimposing relative eddy and through flow at exit is one basis for concept of slip.
Relative eddy
Relative eddy with throughflow

33. Radial Flow Turbine Design
Static pressure gradient across passage causes streamline to shift flow towards suction surface
In reality, the incidence to the rotor varies over the pitch of the rotor as:
due to
Potential and wake interaction with the vane.
Relative eddy effect seen at exit of compressor
Effect produces a LE slip factor
This variation over the pitch leads to an
- optimal incidence and
- optimal number of blades
where the efficiency of the rotor is a maximum.
P=pressure
S=suction

34. Radial Flow Turbine Design
Rotor Inlet Velocity Triangle (with incidence):
Average relative velocity W and avg. relative incidence 2
If we define an incidence factor, l [like  slip factor in compressors]: C2 W2
CR2=CM2
CU2 U2

35. Radial Flow Turbine Design
From the work of Stanitz regarding slip factors:
Note: More Blades,  goes to 1 and inflow becomes radial
Then from the rotor inlet velocity triangles, the inlet flow angle to the rotor is:

36. Radial Flow Turbine Design
Criteria for the Optimal Number of Blades:
Jamieson model

37. Radial Flow Turbine Design
Criteria for the Optimal Number of Blades:
Optimum blade number balances loading & friction
Rohlick model uses (quantities at the inlet to rotor):
Jamieson model

38. Radial Flow Turbine Design
Other Correlations for Optimal Number of Blades (Rohlick results similar to Jamieson):
from Dixon

39. This is to clarify some of the confusing notation in Dixon regarding blade count
Stanitz correlation
uses blade number and flow coefficient to calculate the relative radial turbine exit flow angle.
Other correlations
uses semi-empirical expressions for calculating the optimum [minimum] blade count Z for an optimum efficiency design, where
For such a design the exit flow will be radial [in the absolute frame], therefore 2=0 and the correlations are in terms of the corresponding absolute frame air angles [2], e.g.

40. This is to clarify some of the confusing notation in Dixon regarding blade count
Jamieson
Rohlik