NASA Technical Memorandum 107318 RL10A-3-3A Rocket Engine Modeling Project Michael Binder NYMA, Inc. Brook Park, Ohio Thomas Tomsik and Joseph P. Veres Lewis Research Center Cleveland, Ohio January 1997 NationalAeronauticsand Space Administration TABLE OF CONTENTS Page Introduction ............................................................................................................................................... 1 ° 2. Overview of the RL10A-3-3A Rocket Engine ............................................................................................ 2 2.1 Engine System Configuration and Operation ....................................................................... 2 2.2 Fuel Turbopump ..................................................................................................... 4 2.3 Oxygen (LOX) Pump ...................................................................................................................... 5 2.4 Regenerative Cooling Jacket ....................................................................................................... 5 2.5 Combustion Chamber and Nozzle ......................................................................................... 6 2.6 Valves, Ducts and Manifolds ............................................................................................................. 6 3. Project Organization and Goals ........................................................................................................................... 7 3.1 Turbomachinery Modeling Goals .................................................................................................... 7 3.2 Combustion and Heat Transfer Modeling Goals .......................................................... 8 3.3 Ducts, Manifolds, and Valves Modeling Goals ........................................................................ 8 3A System Modeling Goals .......................................................................................................... 8 4. Component Modeling Results ............................................................................................................................. 9 4.1 Turbomachinery Modeling Results ................................................................................................... 9 4.1.1 Verification of Pump Performance Test Data ............................................................. 9 4.1.2 Extension of Pump Maps for Start and Shutdown Conditions ................................... 9 4.1.2.1 Extension of Pump Maps to Start Conditions ............................................. 10 4.1.2.2 Extension of Pump Maps to Shut-Down Conditions .............................. 11 4.1.2.3 Effects of Density Changes on Pump Performance Models ................... 11 4.1.3 Verification of Fuel Turbine Performance Test Data .................................................. 12 4.1.4 Extension of Turbine Maps ........................................................................................ 12 4.2 Combustion and Heat Transfer Modeling Results ......................................................................... 13 4.2.1 Enhanced Combustion Gas Properties ........................................................................... 13 4.2.2 Cooling Jacket Heat Transfer Model ................................................................................... 13 4.2.3 Thrust Chamber Performance Calculations ........................................................................... 15 4.2_3.1 One-dimensional combustion model layout ....................................................... 15 4.2.3.2 Detailed modeling of the chamber injector ........................................................ 16 4.2.3.3 Nozzle performance models ........................................................................ 16 4.2.3.4 Two-phase flow through nozzle ........................................................... 17 4.2.4 Injector Heat-Transfer Calculations .................................................................... 17 4.3 Duct, Valve, and Manifold Modeling Results ............................................................ 18 4.3.1 Verification of Duct, Manifold Sizes ............................................................................. 18 4.3.2 Prediction of Fluid Frictional Resistances ...................................................................... 18 4.3.3 Modeling of Valve Actuator Mechanisms .................................................................... 19 4.3.4 Modeling of Critical Two-Phase Flow Through a Valve or Orifice ................................ 19 4.3.5 Model of Flow Through Venturi .............................................................................. 21 4.4 The New RL10A-3-3A System Model ............................................................................................ 22 4.4.1 Evaluation of Component Models/Integration With New System Model ....................... 21 4.4.2 Differences Between Start and Shutdown System Models .................................................. 22 5. Modeling Uncertainties ..................................................................................... 22 5.1 Hardware Uncertainties .................................................................. .23 5.2 Valve Uncertainties .............................................................................................. 23 5.3 Uncertainty of Initial Conditions .......................................................................... 24 5.4 Uncertainty in Ignition Time ....................................................................................... 24 5.5 Interaction Between Uncertain Parameters ........................................................................... 25 6. Comparison of System Model Predictions With Test Data .................................................................... 25 6.1 Verification of Steady State Performance Predictions .................... 25 6-2 Verification for Start Transient Simulations .......................................................... 26 6.3 Verification of Shutdown Transient Simulations ....... 27 7. Discussion of Modeling Results ................................................................2.7........................... 7.1 Discussion of Turbomachinery Investigation ................................................................................... 27 7-2 Discussion of Combustion and Heat Transfer Investigation ................................................ 28 7.3 Discussion of Duct, Manifold and Valve Investigation .................................................................. 29 7.4 Discussion of System Model Simulation Results .................................................................................. 29 8. Concluding Remarks .............................................................................................................................................. 29 9. Recommendations for Future Research ........................................................................................ 31 10. Def'mition of Terms ............................................................................................................. 33 11. Acknowledgments .......................................................................................................................... 34 12. Appendixes A RL10A-3-3A Engine System Model for ROCETS .................................................................................... 87 B----Component Modeling of RL10 Fuel and Oxidizer Pumps ............................................................... 89 C---Component Modeling of RL10 Fuel Turbine .................................................................... 109 D---Component Modeling of RL 10A-3-3A Cooling Jacket ................................................ 119 E---Component Modeling of RL10 Injector, Combustion Chamber, and Nozzle ................... 135 F---Component Modeling of RL10 Injector Heat Transfer ............................................................... 149 G---Component Modeling of RL10 Duct Flow ..................................................................... 157 H Modeling of Two-Phase (Liquid/Gas) Flow ................................................................... 163 I---Symbols ......................................................................................................................... 171 J--Glossary of Model Component Names ................................................................................................. 173 13. References ................................................................................................................................................... 175 14. Tables 2.2.1--Summary of Fuel Turbopump Characteristics .............................................................................. 4 2.3.1---Summary of LOX Pump Characteristics ............................................................................................ 5 2.4.1mSummary of Cooling Jacket Characteristics ............................................................................... 5 2.5.1--Summary of Combustion Chamber/Nozzle Characteristics ................................................ 6 2.6.1--Summary of Major Duct and Valve Characteristics ................................................................ 7 4-2.1mDescription of Combustion Property Tables for RL10 Model ...................................................... 35 4.3.I----Comparison of Model Dynamic Volume Sizes ...................................................................... 36 6.1.1--Steady-State Cycle Performance Prediction for the RL10A-3-3A ........................................................ 37 6-2.1--Comparison of Measured and Predicted RL10 Engine Time-to-Accelerate ................................... 38 ii 15. Figures 2.1.1--RL10A-3-3A Engine System Schematic ......................................................................... 39 2.1.2_R.L10 Assumed Valve Schedules for Start Simulation ......................................................... 40 2.1.3--RL10 Assumed Valve Schedules for Shutdown Simulation .............................................. 41 2.2.I----Cross-section of Fuel Pump and Turbine ....................................................................................... 42 2.3.1---Cross Section of LOX Pump and GearBox ......................................................................... 43 2.4.1---Structure of Regenerative Cooling Jacket, Chamber and Nozzle .................................. 44 2.5. I--Injector Design Configuration ....................................................................................... 45 4.1.1---Original Head Map for Fuel Pump 1st Stage (provided by P&W) ............................. .46 4.1.2----Original Head Map for Fuel Pump 2nd Stage (provided by P&W) _._.46 4.1.3--Original Efficiency Map for Fuel Pump 1st stage (provided by P&W ..... .47 4.1.4----Original Efficiency Map for Fuel Pump 2nd stage (provided by P&W__ _.47 4.1.5---Efficiency Speed Correction Map for Fuel Pump - both stages (,provided by P&W) ........... 48 4.1.6--Original Head Map for LOX Pump (provided by P&W) ............................................... _48 4.1.7---Original Efficiency Map for LOX Putnp (provided by P&W) ............................................ .49 4.1.8--Efficiency Speed Correction Map for LOX Pump (provided by P&W) .......................... 49 4.1.9----Generic Wide-Range Performance Maps for Centrifugal and Mixed-Flow Pumps ............... 50 4.1.10---Extended Head Map for Fuel Pump 1st Stage ........................................................... 51 4.1.11--Extended Torque Map (w/o Speed Correction) for Fuel Pump 1st Stage .... 51 4.1.12--Extended Head Map for Fuel Pump 2nd Stage ...................................................... 52 4.1.13---Extended Torque Map (w/o Speed Correction) for Fuel Pump 2nd Stage ........................... 52 4.1.14--Extended Head Map for LOX Pump ...................................................................................... 53 4.1.15--Extended Torque Map (w/o Speed Correction) for LOX Pump ..................................... 53 4.1.16--Fuel Turbine Effective Flow Area Map (provided by P&W and Martin-Marietta) ........... 54 4.1.17--Fuel Turbine Efficiency Map (provided by P&W and Martin-Marietta) ........................ 54 4.2.1---Configuration of Cooling Jacket and Model ........................................................................ 55 4_2.2---Comparison of Full 20-Node Model with 20-Metal-Nod_5-Fluid-Node Model .................. 56 4.2.3----Comparison of Enthalpy-Driven and Temperature-Driven Potential Predictions ................ 57 4.2.4---Predicted Heat Flux Distribution ............................................................................................ 57 4.2.5---Predicted Hot-Wall Metal Temperature Distribution ...................................................................... 58 4.2.6--Predicted Coolant Temperature Distribution ............................................................................ 58 4.2.7--Predicted Coolant Pressure Distribution ....................................................................... 59 4.2.8---c*-Efficiency Maps (from P&W) ................................................................................... 59 4.2.9--TDK/ODE Predictions of RL10A-3-3A Actual Isp, compared to data provided by P&W ..... 60 4.2.10---TDK Predictions of RL10A-3-3A Thrust-Coefficient Efficiency ...................................... 60 4.2.11--Injector Heat Transfer Model Configuration ............................................................ 61 4.2.12--Injector Heat Transfer Rate during start sequence_. __.61 4.3. I--Predicted Mass Flux for Choked Two-phase Flow .... ._.62 4.3.2--RL10 Venturi Flow Parameter Map ...................................................................................... 62 4.4.1--RL10A-3-3A Engine System Model Schematic ........................................................... .63 5.1.1--Variation in Start with Cooldown Valve Effective Area ........................................................... 64 5.1.2--Variation in Start with Turbopump Drag Torque ................................................................. 65 5.2.1--Variation in Start with OCV Actuation Pressure ............................................................ 66 5.2.2---OCV Position during Start as Estimated from Test Data. ........................................................ 67 5.3.1--Variation in Start with Initial Jacket Metal Temperature ................................................ 68 5.4.1--Variation in Start with Assumed Ignition Time-delay ................................................ 69 6.1.1--Steady-State Predictions vs. Measured Values (error distribution) .................................... 70 6.2.1--MES 1 Chamber Pressure - Simulation vs. Ground-Test Data. ................................... .70 6_2.2 MES1 LOX Pump Shaft Speed - Simulation vs. Ground-Test Data ............................... 71 6.2.3--MES1 Fuel Venturi Inlet Pressure - Simulation vs. Ground-Test Data ...... 71 6.2.4--MES1 LOX Pump Discharge Pressure - Simulation vs. Ground-Test Data. ..................... 72 6.2.5--MES1 Turbine Inlet Temperature - Simulation vs. Ground-Test Data ................................. 72 6.2.6---MES1 LOX Pump Inlet Pressure - Simulation vs. Ground-Test Data .................................... 73 6.2.7--MES1 Engine Fuel Inlet Flow - Simulation vs. Ground-Test Data ......................................... 73 6.2.8--MES 1Engine LOX Inlet Flow - Simulation vs. Ground-Test Data. .......................................... 74 6.2.9--MES2 Chamber Pressure during Start - Simulation vs. Ground-Test Data. ............................. 74 6.2.10---MES1 Chamber Pressure - Simulation vs. Centaur Flight Data ................................................. 75 6_..ll--MES1 LOX Pump Shaft Speed - Simulation vs. Centaur Flight Data ........................................... 75 6.2.12_MES1 Turbine Inlet Temperature - Simulation vs. Centaur Flight Data .................................... 76 1.°.11 Figures--Continued 6_.13--MES2 Chamber Pressure - Simulation vs. Centaur Flight Data ................. 76 6.2.14---Predicted Maximum Metal Temperature during Start Transient .................... 77 6.2.15--Predicted Ignitor GOX Supply delta-P during Start (variation with OCV opening pressure)__77 6.3.1--MECO1 Chamber Pressure - Simulation vs. Ground-Test Data. ......... 78 6.3.2 MECO1 LOX Pump Shaft Speed - Simulation vs. Ground-Test Data ............ 78 6.3.3---MECO1 Fuel Venturi Inlet Pressure - Simulation vs. Ground-Test Data ......................... 79 6.3.4--MECO1 LOX Pump Discharge Pressure - Simulation vs. Ground-Test Data. ....................... 79 6.3.5--MECO1 Fuel Pump Inlet Pressure - Simulation vs. Ground-Test Data. ......................... 80 6.3.6--MECO1 LOX Pump Inlet Pressure - Simulation vs. Ground-Test Data .............. 80 6.3.7--MECO1 Engine Inlet LOX Flow - Simulation vs. Ground-Test Data.. ........................ 81 6.3.8---MECO1 Engine Inlet Fuel Flow - Simulation vs. Ground-Test Data ........................ 81 6.3.9mMECO1 Chamber Pressure - Simulation vs. Centaur Flight Data. ........................ 82 6.3.10--MECO1 LOX Pump Shaft Speed - Simulation vs. Centaur Flight Data.. ................ 82 6.3.11--MECO1 Fuel Venturi Inlet Pressure - Simulation vs. Centaur Flight Data. .................. 83 6.3.12--MECO1 LOX Pump Discharge Pressure - Simulation vs. Centaur Flight Data ................. 83 6.3.13--MECO1 Fuel Pump Inlet Pressure - Simulation vs. Centaur Flight Data ......................... 84 6.3.14---MECO1 LOX Pump Inlet Pressure - Simulation vs. Centaur Flight Data_ ................... 84 6.3.15---Range of Predicted Shutdown Profiles (Ground Test Conditions) ............................ 85 6.3.16---Range of Measured Shutdown Profiles (Ground Test Data) ...................................................... 85 iv 1. INTRODUCTION The RL10A rocket engine is an important component of the American space infrastructure. Two RL10 engines form the main propulsion system for the Centaur upper stage vehicle, which boosts commercial, scientific, and military payloads from a high altitude into Earth orbit and beyond (planetary missions). The Centaur upper stage is used on both Atlas and Titan launch vehicles. The initial RL10A-1 was developed in the 1960's by Pratt & Whitney, under contract to NASA. The RL10A-3-3A, RL10A-4, and RL10A4-1 engines used today incorporate component improvements but have the same basic configuration as that of the original RL10A-1 engine. RL10's have been highly reliable servants of America's space program for over 30 years. The RL10's high reliability record has been marred in recent years by two in-flight failures. In the first instance, the cause was initially believed to be Foreign Object Damage of the fuel pump. In the second instance, the cause of failure was determined to be contamination of the fuel pump by atmospheric nitrogen which leaked through a check valve during Munch ascent. The nitrogen froze on the impeller and prevented pump rotation during start. In hindsight, it is likely that the first failure was also due to frozen atmospheric nitrogen. During the course of the accident investigations, the desire for an independent RL10 simulation capability was expressed within NASA and by the Air Force. At that time, the only system models for the engine were the property of Pratt & Whitney and of the Aerospace Corporation. These models are not suitable for public dissemination or government use. The Space Propulsion Technology Division (SPTD) at the NASA Lewis Research Center took up the challenge of creating an independent and accurate model of the RL10A-3-3A engine. The SPTD began developing a computer model of the RL10A-3-3A in 1990 (Reference 1). The first system model was based entirely on data and information provided by Pratt &Whitney. Component data f_om Pratt & Whitney was integrated to form a system model using the ROcket Engine Transient Simulator (ROCETS) code. In 1993, a project team was formed, consisting of experts in the areas of turbomachinery, combustion, and heat transfer. The goals of this project have been to enhance our understanding of the RL10 engine and its components, and to improve the baseline engine system model where possible. A combination of simple engineering correlations, detailed component analyses and engineering judgement have been used to accomplish these tasks. If desired, it should be a relatively simple task to create models of the RL10A-4 and RL10A4-1 as well, using the work done here for the RL10A-3-3A as a foundation. A second goal of this project was to benchmark our tools and methods for modeling new rocket engine components and systems, for which test data may not yet be available. An existing engine with a long test and flight history (the RL10A-3-3A) was used as the validation test-case. In this report, we introduce the reader to the RL10 engine, define the SPTD project organization and goals, briefly discuss results of the various component modeling efforts, and describe the new RL10 system model created. The appendices contain detailed descriptions of the various component analyses performed in support of the project. 2. OVERVIEW OF THE RL10A-3-3A ROCKET ENGINE 2.1 Engine system configuration and operation The RL10 engine is based on an expander cycle, in which the fuel is used to cool the main combustion chamber and the thermal energy added to the fuel drives the turbopumps. A schematic diagram of the engine is shown in Figure 2.1.1. The fuel turbine drives both the fuel and oxidizer pumps (the latter being driven via a gear train). The RL10 engine starts by using the pressure difference between the fuel tank and the nozzle exit (upper atmospheric pressure), and using the ambient heat stored in the metal of the cooling jacket walls. The engine 'bootstraps' to full-thrust within two seconds after ignition. The RL10A-3-3A system normally operates at a chamber pressure of 475 psia, a mixture ratio (O/F) of 5.0, and a thrust of 16,500 lbf (73400 N). Before start, the fuel pump is cooled with hydrogen from the tanks to prevent cavitation at engine start. The fuel cooldown valves (see Figure 2.1.1) are open and the main fuel shut-off valve (FSOV) is closed. The fuel flow is vented overboard through the cooldown valves and does not flow through the rest of the system; the latent heat in the metal of combustion chamber cooling jacket is therefore available to help drive the start transient. The LOX pump is pre-chilled by a flow of oxygen, which passes through the Oxidizer Control Valve (OCV) and is vented through the combustion chamber and nozzle. A typical plot of valve movement during engine start is shown in Figure 2.1.2. To initiate start, the FSOV is opened and the fuel-pump discharge cool-down valve (FCV2) is closed. The interstage cool-down valve (FCV 1) remains partially open in order to avoid stalling of the fuel pump during engine acceleration. The pressure drop between the fuel inlet and the combustion chamber drives fuel through the cooling jacket, picking up heat from the warm metal. This pressure difference also drives the warmed fluid through the turbine, starting rotation of the pumps, which drive more propellant into the system. At start, the OCV also closes partially, restricting the flow of oxygen into the combustion chamber. This is done to limit chamber pressure and ensure a forward pressure difference across the fuel turbine after ignition of the thrust chamber. Ignition of the main combustion chamber usually occurs approximately 0.3 seconds after the main-engine start signal is given (for first-burns). The ignition source is an electric spark. Ignition provides more thermal energy to drive the turbine. As the turbopumps accelerate, engine pneumatic pressure is used to close the interstage cooldown valve completely and open the OCV at pre-set fuel and LOX pump discharge pressures. The OCV typically opens very quickly and the resultant flood of oxygen into the combustion chamber causes a sharp increase in system pressures. During this period of fast pressure rise, the thrust control valve (TCV) is opened, regulated by a pneumatic lead-lag circuit to control thrust overshoot. The engine then settles to its normal steady-state operating point. The primary difference between first and second burn start transient is the initial cooling jacket metal temperature; it is about 540 R for a first start, and about 350 R for the second. Other parameters which may vary from engine to engine, or from run to run include the turbopump friction torque, the propellant tank conditions, and the time of ignition. Figure 2.1.3 shows valve movement for a typical shutdown sequence. The FSOV and Fuel Inlet Valve (FINV) close as the fuel-pump cooldown valves open, allowing fuel to drain out of the system through the overboard vents. The combustion process is soon starved of fuel and the flame goes out. The OCV and Oxidizer Inlet Valve (OINV) begin to close next, cutting off the flow of oxygen through the engine. The turbopump decelerates due to friction losses and drag torque created by the pumps as they evacuate the remaining propellants from the system. Du_dng this process, pump cavitation and reverse-flow are likely. The symbols and model component names used herein are found in appendixes I and J. 2.2 Fuel Turbopump A cross sectional view of the fuel turbopump is shown in Figure 2.2.1. The fuel pump consists of two stages, separated by an interstage duct, which is vented via the interstage cooldown valve (FCV1) during start. Both fuel pump stages have centrifugal impellers, vaneless diffusers and conical exit volutes; the first stage also has an inducer. The RL10 turbine is a two-stage axial-flow, partial admission, impulse turbine (Reference 1). Downstream of the turbine blade rows, exit guide vanes reduce swirling of the discharged fluid. The turbine is driven by hydrogen and powers both the fuel and oxidizer pumps. There are a number of shaft seals which permit leakage from the pump discharge in order to cool the bearings. The fuel pump and turbine are on a common shaft; power is transferred to the LOX pump through a series of gears. The seals, bearings, and gear train all contribute to rotordynamic drag on the turbopump. Table 2.2.1 Summary of Fuel Turbopump Characteristics 1st stage 2nd stage Pump Impeller Diameter 7.07 in 7.07 in Pump Exit Blade Height 0.230 in 0.220 in 16969 ft 17989 ft Pump Headl Pump Mass Howl 6.051 Ibm/see 6.008 lbm/sec Pump Temperature Risel 9.23 R 10.2 R 0.5810 0.5619 Pump Efficiencyt Shaft Speedl 31537 rpm Combined stage Turbine Meanline Diameter 5.90 in Turbine Pressure Ratio (T-T)1 1.39 Turbine Mass Flow1 5.89 Ibm/see Turbine Temperature Dropl 24.5 R Shaft Speedl 31537 rpm 0.0776 lbf.in.sec2 TTPP MDraasgs TMoorqmueent (inocfl.IneOrtxiaPu(minpc)l2. Ox Pump)2 20.0 lbf-in Ivalues taken at typical engine operating point as predicted by the model. 2values are taken with reference to the fuel pump shaft. 4