Modeling and Analysis of Turbojet Compressor Inlet Temperature Measurement System Performance Brian Binkley Aerospace Testing Alliance (ATA) Arnold Air Force Base, TN UTSI January 2011 Air Force Materiel Command Arnold Engineering Development Center Arnold Air Force Base, TN Approved for public release; distribution is unlimited. AEDC PA#

OUTLINE o Introduction/Background o Modeling Work o Eductor Flow o T2 Tube Heat Transfer o Analysis o Conclusions 2 Approved for public release; distribution is unlimited.

INTRODUCTION 3 (not to scale) Hydromechanical Engine Control (Eductor) o T2 bellows and RTD sensors control engine speed, inlet guide vanes, nozzle position and exhaust gas temperature o Ejector pumps T2 air through eductor tubes Hydromechanical Engine Control (Eductor) o T2 bellows and RTD sensors control engine speed, inlet guide vanes, nozzle position and exhaust gas temperature o Ejector pumps T2 air through eductor tubes Ejector T2 Sensors Bellows and RTD) Secondary Stream 150 ⁰ Bend 90 ⁰ Bend Primary Stream exit 1” OD Tube EDUCTOR Flexible Hose (1” ID) Aluminum Duct Engine Bay Compressor Eductor T2 sensors (Bellows and RTD) Bleed Holes Airflow Screen Engine Inlet Radius Approved for public release; distribution is unlimited.

INTRODUCTION 4 (not to scale) T2 Bias o T2 sensors may not indicate true compressor inlet temperature o Components Inlet duct heat transfer (thermal boundary layer) Engine bay air re-ingestion T2 tube heat transfer o Bias can cause engine mis-scheduling T2 Bias o T2 sensors may not indicate true compressor inlet temperature o Components Inlet duct heat transfer (thermal boundary layer) Engine bay air re-ingestion T2 tube heat transfer o Bias can cause engine mis-scheduling Dive Climb Time (sec) Free Stream Total T2 Sensor Inlet Wall Thermal Lag Temperatures Flexible Hose (1” ID) Aluminum Duct Engine Bay Compressor Eductor T2 sensors (Bellows and RTD) Bleed Holes Airflow Screen Engine Inlet Radius Approved for public release; distribution is unlimited.

T2 BIAS MITIGATION APPROACHES 5 SNORKEL CONFIGURATION Eductor pulls air from free stream total temperature Eductor exhausts to engine face Compressor Variable Exhaust Nozzle Inlet Engine Bay Sensors Compressor Variable Exhaust Nozzle Inlet Engine Bay BASELINE CONFIGURATION Eductor pulls air from engine inlet Eductor exhausts to engine face Engine Bay Sensors Bleed Holes Compressor Variable Exhaust Nozzle Inlet Engine Bay BLEED HOLES BLOCKED Bleed holes in front of eductor tube inlet blocked Engine Bay Sensors Bleed Holes Blocked Compressor Variable Exhaust Nozzle Inlet Engine Bay SCOOP CONFIGURATION Eductor pulls from scoop static pressure Eductor exhausts to engine bay Sensors Approved for public release; distribution is unlimited.

OUTLINE o Introduction/Background o Modeling Work o Eductor Flow o T2 Tube Heat Transfer o Analysis o Conclusions 6 Approved for public release; distribution is unlimited.

PURPOSE OF MODELING WORK 7 o Eductor Flow Develop understanding of baseline eductor flow Eliminate fly-fix-fly iterations and ensure safety of test during alternate configuration testing  Maintain positive eductor flow  Optimize mass flow to reduce heat transfer o Heat Transfer Determine the impact of tube heat transfer on T2 bias Approved for public release; distribution is unlimited.

ADDITIONAL CONSIDERATIONS OUTSIDE THE SCOPE OF THIS THESIS o Icing is a concern (particularly for the snorkel configuration) o Aircraft boundary layer ingestion (fluid and thermal) o Upstream flow obstructions / aircraft attitude o Cost/Complexity/Maintenance 8 Approved for public release; distribution is unlimited.

EDUCTOR COMPRESSIBLE FLOW MODEL 9 d Baseline Modeled using experimental results Snorkel Modeled using CFD results b (compressor bleed) T2 Sensors Secondary Stream 150 ⁰ Bend 90 ⁰ Bend Primary Stream e (exit) Scoop Modeled using CFD results EDUCTOR MODEL EDUCTOR INLET MODELS All Configurations Tube loss model from CFD results One dimensional ejector model Approved for public release; distribution is unlimited.

ONE-DIMENSIONAL EJECTOR MODEL 10 b (compressor bleed) T2 Sensors Secondary Stream 150 ⁰ Bend 90 ⁰ Bend Primary Stream e (exit) Subsonic Ejector Secondary Flow Exit Mixed Flow Supersonic Ejector Static Pressures Must Be Equal Primary Flow Exit Mixed Flow Static Pressures Must Be Equal Primary Flow o Without an ejector, the total pressure entering the eductor must be sufficiently higher than the exit static pressure to overcome losses PTd > PSe o Ejector adds energy to the system and pumps the air through the T2 tube and can overcome an adverse pressure gradient PTd < PSe d (T2 tube) A.Constant area expansion process High velocity primary stream lowers the static pressure in the diffuser (pumping for secondary stream) B.Isentropic mixing Mass, linear momentum and energy conserved Static pressure of both streams must be equal-couples equations Resulting increase in secondary stream total pressure and velocity C.Total pressure of mixed stream now higher than exit static pressure Secondary Flow Approved for public release; distribution is unlimited.

ONE-DIMENSIONAL EJECTOR MODEL 11 b (compressor bleed) T2 Sensors Secondary Stream 150 ⁰ Bend 90 ⁰ Bend Primary Stream e (exit) Subsonic Ejector Secondary Flow Exit Mixed Flow Supersonic Ejector Static Pressures Must Be Equal Primary Flow Exit Mixed Flow Static Pressures Must Be Equal Primary Flow o Without an ejector, the total pressure entering the eductor must be sufficiently higher than the exit static pressure to overcome losses PTd > PSe o Ejector adds energy to the system and pumps the air through the T2 tube and can overcome an adverse pressure gradient PTd < PSe d (T2 tube) Secondary Flow PT, TT and Geometry Known PS guessed (iteration req’d) PS Known Approved for public release; distribution is unlimited.

MODEL DEVELOPMENT PROGRESSION 12 Literature review for existing ejector models 3D CFD on eductor tubes Update ejector model Validate ejector model updates Calibrate existing model to match CFD results 3D CFD for Snorkel Combine scoop CFD model results with eductor model 3D CFD for Scoop Combine scoop CFD model results with eductor model Calibrate eductor model to ground test data Preliminary snorkel/eductor predictions Preliminary scoop/ eductor predictions Updated predictions Baseline T2 Tube Mass Flow (lbm/sec) Percent Corrected Engine Speed Derived from ground test data Calibrated eductor model Curve Fit Percent Corrected Engine Speed Baseline T2 Tube Mass Flow (lbm/sec) Derived from ground test data Eductor model Curve Fit Approved for public release; distribution is unlimited.

T2 Sensors Bellows and RTD) Secondary Stream 150 ⁰ Bend 90 ⁰ Bend Primary Stream PSe PTd MODEL PREDICTIONS OF MINIMUM REQUIRED EDUCTOR PRESSURE RATIO 13 o Eductor pressure ratio captures the performance of the eductor inlet configurations (PTd) as well as the effects of alternate eductor exit locations (PSe) o Ejector allows pumping of secondary stream in adverse pressure gradient o Eductor pressure ratio captures the performance of the eductor inlet configurations (PTd) as well as the effects of alternate eductor exit locations (PSe) o Ejector allows pumping of secondary stream in adverse pressure gradient Approved for public release; distribution is unlimited.

OUTLINE o Introduction/Background o Modeling Work o Eductor Flow o T2 Tube Heat Transfer o Analysis o Conclusions 14 Approved for public release; distribution is unlimited.

EDUCTOR HEAT TRANSFER MODEL 15 Flexible Hose Aluminum Duct Engine Bay Compressor Eductor T2 sensors Airflow Screen Engine Inlet Radius n+1 n Tout n Tin n+1 Tout n+1 Tin n+2 TT b n+1 Tw n+1 Tw n Tin n Tout n-1 n (not to scale) ToutAir temperature leaving element TinAir temperature entering element TTbTube external air temperature boundary condition TwTube wall temperature o Model of time dependent convection/conduction through tube into air stream o No heat sources o Discretized geometry Each element has constant thermal properties but can vary from element to element Tube wall temperature is uniform in each element but may vary from element to element No conduction along length of element Air properties iterated inside each element o March along tube length to solve elements sequentially, repeat in time Approved for public release; distribution is unlimited.

HEAT TRANSFER SOLUTION 16 Biot Number o If Bi<<1 then resistance to conduction is negligible and wall temperature assumed to be uniform o Biot number checked for each tube element o Heat transfer solution selected based on Biot number o If Bi<<1 then resistance to conduction is negligible and wall temperature assumed to be uniform o Biot number checked for each tube element o Heat transfer solution selected based on Biot number Lumped Capacitance Model (Bi ≤ 0.1) TT b n Tw n Heat Equation (Bi > 0.1) roro riri Tw n =T(r,t) TT b,h TT b n Tw n Approved for public release; distribution is unlimited.

HEAT TRANSFER COEFFICIENTS 17 EXTERNAL CONVECTION INTERNAL CONVECTION o Gnielinski Relationship Uniform surface heat flux and temperature Smooth or rough wall 0.5 ≤ Pr ≤ ≤ Re ≤ 5x10 6 o Hilpert’s Empirical Correlation Circular and non-circular tubes Pr ≥ ≤ Re ≤ 4x10 5 DTube DiameterNuNusselt Number kTube Thermal ConductivityReReynolds Number hHeat Transfer CoefficientPrPrandtl Number Approved for public release; distribution is unlimited.

x=0 i=1 x=L i=n x/L=0.4 HEAT TRANSFER MODEL CONVERGENCE T 2 o 2-Norm of error in tube air temperature ||T|| 2 o Initial air temperature at each element equal to converged temperature of previous element o Maximum error at x/L=0.4. Initial guess improves as grid density increases. o Control volume independence with 8x or higher grid density o 2-Norm of error in tube air temperature ||T|| 2 o Initial air temperature at each element equal to converged temperature of previous element o Maximum error at x/L=0.4. Initial guess improves as grid density increases. o Control volume independence with 8x or higher grid density T at x/L=0.4 (deg. F) Control Volume Independent Approved for public release; distribution is unlimited.

GROUND RUN 19 ~130 second dwell time Bleed valve openBleed valve closedAugmentation Corrected Engine Speed (% RPM) Approved for public release; distribution is unlimited.

MEASURED TUBE AIR TEMPERATURE RISE % Speed90% Speed80% Speed60% Speed TT d,1 TT d,2 ΔT=TT d,2 – TT d,1 TT b Bleed valve closed Tube air temperature measurements Augmentation 50% Speed Approved for public release; distribution is unlimited.

TUBE AIR TEMPERATURE RISE PREDICITONS 21 Measurement Prediction with Estimated Boundary Condition TTb = 60%TT0 + 40% Average Forward Bay Air Temperature Prediction (TTb= Average Forward Bay Air Temperature) o Bleed valve closes and nozzle pumping above 80% engine speed o Heat transfer sensitive to forward engine bay air temperature o Uncertainty in forward engine bay air temperature o Tube heat transfer is a significant contribution to T2 bias o Bleed valve closes and nozzle pumping above 80% engine speed o Heat transfer sensitive to forward engine bay air temperature o Uncertainty in forward engine bay air temperature o Tube heat transfer is a significant contribution to T2 bias Approved for public release; distribution is unlimited.

OUTLINE o Introduction/Background o Modeling Work o Eductor Flow o T2 Tube Heat Transfer o Analysis o Conclusions 22 Approved for public release; distribution is unlimited.

EDUCTOR PERFORMANCE PREDICTIONS (GROUND RUN) 23 d T2 Sensors Secondary Stream 150 ⁰ Bend 90 ⁰ Bend e (exit) Snorkel Scoop Baseline Minimum for positive flow Approved for public release; distribution is unlimited.

T2 TUBE MASS FLOW PREDICTIONS (GROUND RUN) 24 Snorkel Scoop Baseline Approved for public release; distribution is unlimited.

BASELINE T2 TUBE HEAT TRANSFER PREDICITON (GROUND RUN) 25 INCREASING ENGINE POWER SETTING Average Forward Engine Bay (Air Temperature) Average Forward Engine Bay (Air Temperature) Predicted Tube Temperature at T2 Sensor (Wall Temperature) Predicted Tube Temperature at T2 Sensor (Wall Temperature) o Heat transfer model solves for tube wall temperature (orange line) o Average forward engine bay air temperature is the tube external temperature boundary condition o Time dependent predicted tube wall temperature behaves as expected o Heat transfer model solves for tube wall temperature (orange line) o Average forward engine bay air temperature is the tube external temperature boundary condition o Time dependent predicted tube wall temperature behaves as expected Ambient Air Temperature Approved for public release; distribution is unlimited.

BASELINE T2 TUBE HEAT TRANSFER PREDICITON (GROUND RUN) 26 INCREASING ENGINE POWER SETTING o Tube heat transfer is a function of tube wall temperature and convecting air inside and outside of tube o Tube heat transfer is a significant contribution to T2 bias (predicted up to 14°F) o Tube heat transfer is a function of tube wall temperature and convecting air inside and outside of tube o Tube heat transfer is a significant contribution to T2 bias (predicted up to 14°F) Predicted T2 with Tube Heat Transfer (Air Temperature) Predicted T2 with Tube Heat Transfer (Air Temperature) Measured T2 Sensor (Air Temperature) Measured T2 Sensor (Air Temperature) Contribution of Bay Air Re-ingestion Contribution of T2 Tube Heat Transfer 14° Approved for public release; distribution is unlimited.

FLIGHT MANEUVER 27 Time (sec) Dive Climb Mach 1.0 Mach Altitude Time (sec) Percent Corrected Engine Speed Dive Climb Dive Climb Time (sec) Free Stream Total T2 Sensor Inlet Wall Thermal Lag Altitude and Mach Number Temperatures Bay Air Re-ingestion (Pressure Ratio Across Bleed Holes) Time (sec) Engine Bay Air Re-ingestion Dive Climb 1.0 Bay Ps Inlet Ps Approved for public release; distribution is unlimited.

EDUCTOR PERFORMANCE PREDICTIONS (FLIGHT MANEUVER) 28 Climb Dive Snorkel Scoop Baseline Minimum for positive flow d e (exit) Scoop/eductor performance drops below baseline at high aircraft Mach numbers due to bay pressurization and total pressure loss in T2 tube Approved for public release; distribution is unlimited.

T2 TUBE MASS FLOW PREDICTIONS (FLIGHT MANEUVER) 29 Baseline Scoop Snorkel Lower scoop/eductor T2 tube mass flow due to increased adverse pressure gradient across eductor Approved for public release; distribution is unlimited.

BASELINE T2 TUBE HEAT TRANSFER PREDICITON (FLIGHT MANEUVER) 30 Free Stream Total Average Forward Engine Bay (Air Temperature) Average Forward Engine Bay (Air Temperature) Predicted Tube Temperature at T2 Sensor (Wall Temperature) Predicted Tube Temperature at T2 Sensor (Wall Temperature) As with the ground test predictions, the time dependent tube wall temperature prediction behaves as expected Approved for public release; distribution is unlimited.

BASELINE T2 TUBE HEAT TRANSFER PREDICITON (FLIGHT MANEUVER) 31 Free Stream Total Predicted T2 with Tube Heat Transfer (Air Temperature) Predicted T2 with Tube Heat Transfer (Air Temperature) Measured T2 Sensor (Air Temperature) Measured T2 Sensor (Air Temperature) Engine Bay Air Re- ingestion 50% of T2 bias attributed to T2 tube heat transfer outside of engine bay air re-ingestion region during transient maneuvering T2 Bias due to inlet duct heat transfer and/or engine bay air re-ingestion T2 bias due to T2 tube heat transfer Approved for public release; distribution is unlimited.

OUTLINE o Introduction/Background o Modeling Work o Eductor Flow o T2 Tube Heat Transfer o Analysis o Conclusions 32 Approved for public release; distribution is unlimited.

CONCLUSIONS Validated engineering model matches baseline ground test data well and provides good snorkel and scoop predictions Snorkel is the best configuration –Highest eductor pressure ratio in flight and on the ground –Lowest probability of reversed eductor flow –Highest T2 tube mass flow rate in flight and on the ground –Highest potential for most T2 bias mitigation Scoop configuration unnacceptable –Potential for T2 tube mass flow and eductor pressure ratio to be lower than baseline levels at some flight conditions –Potential for increased T2 bias and engine mis-scheduling Benefits provided by eductor flow and heat transfer modeling and analysis –Identified deficiencies in alternate configuration designs –T2 tube heat transfer can be as much as half of the T2 bias –Assisted determination of instrumentation requirements for flight test 33 Approved for public release; distribution is unlimited.