1. Class 9: Turbomachine Design
Turbomachine comprised of rows of stators and rotors
can be as little as single rotor row (fan)
Compressor Modeling
0D: Thermodynamic or cycle analysis
Provides inlet / exit thermodynamic and efficiency for each component
1D: Actuator disc or meanline aerodynamic analysis
First thermodynamics, then velocity triangles
specify area or Cx
model spanwise effects
no specified efficiency, but calculate losses of specified blades (CML)

2. Compressor Design
0-dimensional analysis: cycle code [NPSS, SOAPP, DIGITEM]
treat compressor as a module, element or single unit that performs performance calculations
specify inlet, outlet bleed flows
call compressor map based on experimental data
calculates unscaled performance based on user supplied maps W
Compressor
Turbine

4. Numerical Propulsion System Simulation (NPSS) NASA Glenn RC Code
NPSS is a full propulsion system simulation tool used to predict and analyze the aerothermodynamic behavior of gas turbine engines.
NPSS is a numerical "test cell" that enables engineers to create complete engine simulations.
NPSS allows engine designers to analyze different parts of the engine simultaneously, perform different types of analysis simultaneously (e.g., aerodynamic and structural).

5. JT8D-200 Series Engine

6. Ex.:Twin Spool Unmixed Flow Turbofan

7. 0D Model Set-up and Execution
Double Click on bam.bat file in bam directory
Open File “class_shaft.bam” using File Open menu.
Model is a Single Spool Turboshaft
Inlet -> High Compressor-> Burner-> High Turbine-> Nozzle
See Figure 1 for Block diagram. This graphic will appear in the lower half of the Graphical User Interface (GUI) when the model is loaded.
Design Point
Click on “Design Point” tab in GUI to vieiw design inputs.
Change viewer.switchSolverOutput value to “ON”
Change viewer.switchBasicOutput value to “ON”
Change viewer.switchCsvOutput value to “ON”
Select “Apply”.

8. 0D Model Set-up and Execution
Variable Output List
Click on “Viewer Var List” in GUI to view output parameters.
At bottom of GUI window – input desired output file name (e.g. “test”)
Select “Reset” then “Apply”.
Parameters Definitions
Click on small arrow on upper left corner of GUI to view parameter definitions and units.
Execute
Click on the “Design Point” box at the bottom of the GUI.
Click on “Execute”.
Output
test.bamout – text output.
test.csv – comma separated variable output readable in excel.

9. 0D Model Set-up and Execution
Run off-design parametrics
[1] over operating line,
[2] over constant speed,
[3] for different efficiencies to
plot PR versus mass flow.

10. Twin Spool Unmixed Flow Turbofan–Configuration
Turbofan Model at the Design Point and Offdesign
FN = 5000 lbf, OPR = 25, Wc Inlet = 1000 lbm/sec
Baseline Component Polytropic Efficiencies at 90%
Fan Pressure Ratio = 1.6, LPC PR = 2.5, HPC PR = 10.0
What are T3, T4, Wfuel, N2C25, HPC WcIn, HPC had, Fg, and Fram ?
Set up an Off-design sweep of N2HPC from 10,000 to 11,400 RPM
Plot the HPC Operating Line and HPC had vs. HPC WcIn Wc
Secondary Nozzle
Primary Nozzle T4
OPR T3

11. Design Point

13. Off-Design sweep of N2HPC
Include this code for generating the sweep of N2HPC from 10,000 to 11,400 rpm
Remember to click “Apply” before executing the run.

15. Design point and Offdesign sweep, relative to peak had
Idle
HPC Off-design Results
Maximum adiabatic efficiency occurs lower on the operating line
Peak Efficiency = 88% adiabatic
Peak Efficiency occurs near 10,900 RPM (corrected speed)
Set HPC Design Pressure Ratio to 8.31
Resize Engine to achieve HPC WcIn = 50 lbm/sec

16. Updating the HPC design data
On the “Design Point” page update the HPC design information based on the off-design run at 10,900 RPM
Remember to click “Apply”

17. Updating the HPC design speed
Remember to click “Apply”

18. Additional Balances
Under “Additional Balances” – deactivate the balances previously set-up for
Core Size
Velocity Jet Ratio
Add a new balance for HPC Inlet flow CmpH.WcIn
Remember to click “Apply” before executing the run.
balance names are user defined
The new balance allows the engine bypass ratio to be changed to meet the HPC inlet flow required at maximum had.

19. Results Interesting Results Fuel consumption decreases .06%.
Over 14,366 lbm/year fuel saved for a twin engine aircraft flying approx 18 hr/day, including 12 hours of cruise flight per day.
$68,000/yr saved (Jet A $4.73/gal)
Turbine Cooling Air Temperature decreases 6%
OPR decreases 16.8% while BPR increases 16.3%

20. Single Spool Turboshaft – Overview
Primary Cycle Parameters
Optimized to Minimize Fuel Consumption and Maximize Power
Overall Pressure Ratio (OPR or P3QP2)
Cycle Temperature (RIT or T4)
Engine “Sized” to Meet Power Demands (Design Point)
Inlet Flow (Wc) Set to Match Power Requirement
Note – Sizing is Direct Driver on Weight
Generally Speaking
Increasing T4 Reduces Engine Size for a Given Power Requirement
Increasing OPR Reduces Fuel Consumption
To a Point, then the Trend Reverses
Component Efficiencies Strongly Influence These Trades
Same Holds for Cooling Air, Parasitic Losses, etc.

21. Twin Spool unmixed flow Turbofan – Overview Engine Rematch Example
Primary Cycle Parameters
Optimize to Minimize Fuel Consumption and Cruise Thrust
Overall Pressure Ratio (OPR or P3QP2) was set at 25.0
Spool mechanical speeds set
3000 RPM for Fan, Low PC, and Low PT
12000 RPM for High PC and High PT
Bypass Ratio set 7.0
Core Size set at 8.0 lbm/sec
Jet Velocity Ratio set at 0.80 (NozSec.Vactual/NozPri.Vactual)
Component polytropic efficiencies set
Fan hp = 0.90
LPC, HPC, HPT, LPT hp = 0.90

22. Engine Rematch example
Engine “Sized” to Meet Power Demands (Design Point)
5000 lbf Net Thrust at 35,000 ft., Mach 0.80
Design Inlet Flow (Wc) Set to meet Thrust Requirement
1000 lbm/sec (NPSS will use this value at the start of solver iterations)
Generally Speaking
Increasing T4 Increase Cycle Efficiency and Reduces Engine Size However, the turbines are subjected to higher temperatures
Increasing OPR Reduces Fuel Consumption
However, the temperature of the engine cooling air increases
More air required to achieve required cooling
Reduced part life at elevated operating temperatures
In this example we will examine the effects of resetting the HPC operating parameters at the design point (to highest had)

23. Turbofan Cruise to Midflight Idle

24. Turbofan Cruise to Midflight Idle

25. Turbofan Cruise to Midflight Idle

26. Turbofan Cruise to Midflight Idle

28. Single Spool Turboshaft Configuration
Construct and Execute a Cycle for the Following
T4 = 2000° R, OPR = 12, 100#/s Wc
Baseline Component Efficiencies =85% (HPC and HPT)
Burner Pr Loss = 5%, Nozzle PR = 1.05
What Flow is Required to Produce SHP
What is the Impact of Changing T4 +500°
What About Increasing Component Efficiency 5% Wc
OPR
Burner
Pr Loss T4
Nozzle PR

29. Thermodynamic View of the Gas Turbine Cycle
Ideal Brayton Cycle
Realistic Brayton Cycle With Nonisentropic
Compression and Expansion Paths
Constraints on Gas Turbine Cycle Parameters

30. Design Constraints Coupling Compressor & Turbine
Minimum (ambient) and maximum (turbine metalography limits) temperature levels set design cycle
Low compressor Pr [cycle 1-K1-K2-K3-K4]
absorbs little work and turbine produces little work.
High compressor Pr [cycle 1-B2-B3-B4]
results in high compressor exit temperature  little heat can be added (by combustor) without exceeding turbine limits

31. Typical HPC (N2) Compressor Map Over Range of Operation

32. Meanline Calculations
Meanline is the midpoint between hub and tip
Meanline represents the first solution for velocity triangles of machine
Calculations performed at one radial location for each axial station
Many Uses for Meanline Calculations
Predict efficiency potential
Optimize configurations
Predict off-design trends
Convert P0 & T0 data to Loss & Velocity diagrams, stage characteristics
Basis for stability analysis

33. Meanline Calculations
Meanline Calculation Types
Design - Given Po & To, calculate velocity diagrams & select airfoils
Off-design - Given airfoils, calculate velocity diagrams,
P0 & T0
Cascade data correlations available in meanline
programs

34. Design Meanline Calculations
Known for Rotor Leading Edge:
P01 T01 m (flow)
Aan1 Aan2 (Annulus area)
1 U1 = U2 = U
 R hp
Sufficient airfoil parameters
Calculate
Pr,  if loss coefficients and rotor exit angle are known
Rotor exit angle 2 and loss coefficients of rotor exit Po2 and To2 known

35. Design Meanline Calculations
All problems use same technique at Rotor Leading edge.
Determines M1
M1  P/P01, T/T01 from isentropic relations
P01, T01, P/P01, T/T01  P1, T1
M1, T1  C1
C1, U, 1  Cu1, Cx1, Wu1, W1, 1
W1, T1  M1R
M1R, P1, T1  T01R, P01R
This completely determines flow at rotor leading edge.

36. Design Meanline Calculations
Design Problem:
Know P02 & T02  (Note that an efficiency is
used here)
Find Exit Velocity, Angle & 
By Euler's Equation:

37. Design Meanline Calculations
Guess Cx2
Cu2 [from Euler equation], Cx2  C2, 2
C2, To2  T2
C2, T2  M2, FP02

38. Design Meanline Calculations
Vary Cx2 until continuity matches.
M2, P02, T02  P2, T2
U, Cu2  Wu2
Cx2, Wu2  W2, 2
T2, W2  M2R
T2, P2, M2R  T02R, P02R

39. Design Meanline Calculations
Now have complete exit velocity diagram
Method applies to turbine & compressor
Determine loss coefficients:

40. Design Meanline Calculations
Can analyze Loss vs Incidence, Dfactor, Mach number, etc.
Can use given P0 & Loss correlations to determine efficiency, mean camber, loading, solidity, etc.

41. Off-Design Meanline Calculations
Off-Design Problem for Compressor:
Know 2 &  for given airfoil shape, Determine Pr & 
Solve Continuity in the Rotating Reference Frame:

42. Off-Design Meanline Calculations
FPt2R  M2R
M2R, To2R, Po2R  T2, P2, W2
W2, 2, U  Wu2, Cx2, Cu2, C2, 2
C2, T2  M2
M2, T2, P2  Po2, To2
Po1, Po2, To1, To2  Pr, 

43. Off-Design Meanline Calculations
For the turbine, knowing 2 & (or Y)
Guess M2R:
and:
Vary guessed M2R to convergence.Same solution as compressor except different loss coefficient definition!

44. Compressor Design Meanline Example
Given:
rotor stator
mass flow = 100 lb/sec
 = 1.4
Wheel speed = 1350 ft/sec, constant
Find: rotor and stator loss coefficient []
rotor and stator solidity []

45. Compressor Design Meanline Example
Continuity can be solved at stations 1 & 3:
Iteration at station 1:
Guess a1  M1 from FP0
From M1, T01  T1, C
From C, a1  Cx1, Cu1
From Cx1, Aan1  m (flow)
Same iteration can be done at station 3. This gives:

46. Compressor Design Meanline Example

47. Compressor Design Meanline Example
Euler's Equation needed at station 2
Iteration:
Guess

48. Compressor Design Meanline Example

49. Compressor Design Meanline Example
Mach numbers that satisfy continuity have been found at all stations. The velocity diagram is solved as usual:

50. Compressor Design Meanline Example
Relative frame total pressure is needed for rotor 
Loss Coefficients [Compressible]:

51. Compressor Design Meanline Example
Solidity using So