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)

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

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).

JT8D-200 Series Engine

Ex.:Twin Spool Unmixed Flow Turbofan

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”.

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.

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.

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

Design Point

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.

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

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”

Updating the HPC design speed Remember to click “Apply”

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.

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%

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.

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

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)

Turbofan Cruise to Midflight Idle

Turbofan Cruise to Midflight Idle

Turbofan Cruise to Midflight Idle

Turbofan Cruise to Midflight Idle

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 10000 SHP What is the Impact of Changing T4 +500° What About Increasing Component Efficiency 5% Wc OPR Burner Pr Loss T4 Nozzle PR

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

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

Typical HPC (N2) Compressor Map Over Range of Operation

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

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

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

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.

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

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

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

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

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.

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

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, 

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!

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 []

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:

Compressor Design Meanline Example

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

Compressor Design Meanline Example

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

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

Compressor Design Meanline Example Solidity using So