Document
Model Preparation,
Operations, and Access
Presentation to
AVT - 328 Technical Course
Impact and Advanced Implementation of
Cryogenics in Aerodynamic Testing
Scott GOODLIFF, USA
AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 1
Agenda
Model Preparations Pre - Assembly Model Assembly Instrumentation Integration Surface Preparation Pre - Test Model System Checks Operations Tunnel Conditioning Testing / Data Acquisition Test Matrix Sequencing Test Envelopes Model Access Cryogenic Model Access Background Facility Processes AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 2
Model
Preparations
AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 3
Pre - Assembly
Importance of pre - test model preparation is amplified for cryogenic models Complexity of models, test environment, and integration of instrumentation make it difficult and time consuming to correct a problem later Better preparation = better chance of successful test !
Typical Pre - Test Tasks Clean Model Hardware - cryogenic testing require models to be fabricated from special alloys that can easily rust - models pulled from storage need to be cleaned of oils or other hydrophobic agents prior to assembly Purge Model Pressure Tubing - dry air or nitrogen purge on internal pressure tubing to eliminate moisture contamination - any moisture in the tubes could freeze and compromise pressure measurements during the test Model Preparations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 4
Pre - Assembly, Continued
Typical Pre - Test Tasks Clean all Fastener Holes - clean threaded holes and pin holes, tape over them to prevent contamination prior to assembly , saves time and mitigates assembly problems Rapid Prototyping - 3 - D printed parts and model components can be extremely beneficial for verifying fit of internal instrumentation, fit of cables and tubing, and identifying assembly sequences Model Preparations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 5
Pre - Assembly, Continued
Typical Pre - Test Tasks Model Fasteners - cryogenic models require specialty fasteners that can take time to procure and/or fabricate, possible long - lead items (certs required for fasteners used in critically stressed areas) - most common fastener material for cryogenic applications is A286 o - high - strength steel alloy ( Unbrako or equivalent) can be used down to - 50 F or 225K - common pin material is Nitronic 60/40, or VascoMax if more strength is needed Cryogenic Testing of Components - model components can be tested cryogenically to identify any thermal issues before the model is assembled Need photo of component cryo test Model Preparations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 6
Model Assembly
Assembly of cryogenic models for high Reynolds numbers requires special attention in several areas Model assembly typically completed outside of the test section Minimizes moisture from personnel presence Assembly issues, troubleshooting, and instrumentation checkouts can be more effectively worked outside of the tunnel Model Assembly Focal Points Fastener Retention - i n most cases, 2 forms of retention are required for each fastener - acceptable forms of retention for cryogenic applications torque Loctite threadlocker safety wire secondary retention fastener (dowel pins or pull - pins) Model Preparations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 7
Model Assembly, Continued
Model Assembly Focal Points Sealing of Model Joints - thermal contraction effects can create unwanted gaps in model joints - flow through gaps that are not a part of the design can compromise vehicle aerodynamics - sealer is typically applied between all model joints Examix Xantopren RTV - consideration must be given to effect of sealant on fit and finish of joints Does the sealant create a gap or step in joints that would be more detrimental than flow?
Model design provision for sealant (i.e. trench, relief, etc.)?
Model Preparations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 8
Model Assembly, Continued
Model Assembly Focal Points Metric - to - Non - Metric Seals - flow blockers sometimes required for metric - to - non - metric boundaries - seals must remain flexible at cryogenic temperatures (fiberglass is common) - fabrication and fit of these seals is a black art NON - METRIC STRUT seal must make contact with opposing surface in order to seal, but must not affect balance measurements full model cryo SEAL cycle used to check seal effects at test METRIC MODEL temperature Model Preparations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 9
Model Assembly, Continued
Model Assembly Focal Points Bolt Hole Preparation - bolt hole filler retention is critical - filler changes or departure can affect results at high Reynolds number - bolt/pin hole countersinks and counterbores can be scuffed up to provide filler material with better adhesion - sometimes there simply isn’t enough depth to the hole, consider changing filler material or scuffing up the bolt head Model Preparations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 10
Instrumentation Integration
Models are typically large enough to host an array of sensors, transducers, and other measurement devices Special considerations given to internal instrumentation which may also be exposed to cryogenic temperatures Applies to thermally sensitive measurement devices as well as cabling/tubing Instrumentation Focal Points Cabling/Tubing Considerations CABLING/TUBING CONDUIT - slack and “service loops” should be provided to compensate for thermal contraction - tie - downs and metric points of attachment should allow cabling/tubing to slide freely (zip ties, shrink tubing, etc.)
- special emphasis on metric - to - non - metric boundaries, critical for high - quality SLACK AND SERVICE LOOPS force/moment measurements Model Preparations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 11
Instrumentation Integration, Continued
Instrumentation Focal Points, Continued Instrumentation Thermal Considerations - develop thermal strategy for instrumentation calibrate device(s) at various temperatures to compensate for it keep device(s) at constant temperature - installation of insulated heated enclosure(s) to keep device(s) at constant temperature Force/Moment Balance Thermal Conditioning - balance heating/cooling line installed for expediting balance thermal conditioning - dry nitrogen gas is used in a warm or cold state - dry nitrogen purge used on balance to keep moisture/condensation away from strain gauges during model accesses HEATED ESP ENCLOSURE Model Preparations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 12
Surface Preparation
State of model flow surfaces critical for high Reynolds number testing Thin boundary layer makes small protuberances on model detectable in force and pressure data Many techniques and processes used to prepare a model surface for high Reynolds number testing Key Surface Preparation Techniques and Processes Surface Roughness - typical model surface roughness after fabrication of <64 m in or <1.6 microns Ra - roughness measurements made with profilometer before and after the test to document the state of key model surfaces and ensure model meets requirements Need photo of profilometer in use from ETW Model Preparations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 13
Surface Preparation, Continued
Key Surface Preparation Techniques and Processes, Continued Model Filler - many different types for different applications Evercoat EVERCOAT primary filler material for bolt holes and other model filler requirements (polyester glazing putty) UV filler combination of quartz powder and Loctite, requires UV light to cure, slightly better performance and adhering capability than Evercoat but much harder to work with Two - part RTV used in filler and sealing applications requiring a more flexible solution, two - part used in the tunnel due to the dry conditions Need photo of ETW Epoxy model filler example used for permanent filling applications, 9309 epoxy + carbonspheres or 9394 epoxy used successfully Model Preparations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 14
Surface Preparation, Continued
Key Surface Preparation Techniques and Processes, Continued Paint Application - temperature sensitive paint (TSP), pressure sensitive paint (PSP), and other paint applications supporting flow visualization - paint typically applied outside of the tunnel to prevent tunnel contamination and enhance curing - critical to properly prime the model to maximize adhesion of subsequent paint layers Model Deformation Targets - Facility dependent method for application Flourescent marker Need photo of ETW Thin self - adhesive transfer targets targeted model Model Preparations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 15
Surface Preparation, Continued
Key Surface Preparation Techniques and Processes, Continued Fixed Boundary Layer Transition - many methods of application approved for cryogenic use - in all cases, especially self - adhesive dots, proper cleaning of the metal surface is critical for maximum adhesion self - adhesive dots - most commonly used type of fixed transition - available in many heights - typically vinyl, but heights less than 0.002 inches or 0.05 mm may be foil epoxy - epoxy dots more durable than self - adhesive, but more labor intensive for application, requires shaving to proper height grit - carborundum grit used for less - precise applications in which the drag increment of the grit itself is less critical (fuselage components) Model Preparations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 16
Pre - Test Model System Checks
Model integrated system check completed at cryogenic test temperatures outside of the tunnel Used to validate thermal conditioning of all instrumentation, verify/characterize proper balance response throughout test temperature range, and ensure balance signals are free from fouling contamination Model Preparations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 17
Operations
Need ops photos from European facilities AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 18 NTF Test Envelope Air Mode at 120°F
Test Envelopes
NATIONAL TRANSONIC FACILITY 60 MW 55 MW AIR MODE, 120ºF 24 Need to 50 MW 105 psi P 45 MW T annotate in 40 MW 35 MW metric units 90 psi P T 30 MW 18 75 psi P T 2500 psf 60 psi P T 45 psi P T 2000 psf Reynolds Number (million/ft) 120 psi P T 30 psi P T 1500 psf Reynolds Number (per foot) 1000 psf 15 psi P T 500 psf 250 psf 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 Operations Mach Number Mach Number AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 19 NTF Test Envelope Nitrogen Mode at -250°F
Test Envelopes
120 psi P T NATIONAL TRANSONIC FACILITY 4500 psf CRYO MODE, - 250ºF 105 psi P T 4000 psf 3500 psf 90 psi P T 3000 psf Need to annotate in 2500 psf 75 psi P T metric units 2000 psf 60 psi P T 1500 psf 1000 psf 45 psi P T Reynolds Number (million/ft) 500 psf 30 psi P T Reynolds Number (per foot) 250 psf 18 psi P T 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30 Operations Mach Number Mach Number AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 20
Test Envelopes
Need envelopes from European facilities Operations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 21
Tunnel Conditioning
Tunnel internal environment and thermal state must be properly conditioned prior to data acquisition Processes for conditioning the tunnel similar for all facilities in cryogenic mode Some processes not applicable to tunnels capable of testing in air mode Key Processes for Tunnel Conditioning Gas Exchange - not applicable for testing in air mode - all air must be purged from tunnel circuit and replaced with nitrogen gas o - typically completed at near - ambient conditions (100 F or 310K) - process also used to eliminate any residual moisture in the tunnel - entire process takes several hours to complete - process reversed to go from nitrogen mode to air mode testing (NTF only) Operations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 22
Tunnel Conditioning
Key Processes for Tunnel Conditioning, Continued Cooldowns - liquid nitrogen injected into tunnel circuit to cool the freestream down to desired test temperature - completed at very low speed (~Mach 0.1) to minimize nitrogen consumption o - typical cooldown rate of 1.2 F or 0.7K per minute (verify rate at ETW) o - can take many hours to cool down to - 250 F or 116K Warmups - fan heat used to warm up tunnel (no nitrogen injection needed) - rate of warmup same as cooldown rate Model/Structure Conditioning - model and tunnel internal structure thermally conditioned to near freestream temperature - critical for stabilizing freestream flow and obtaining high - quality data - model, tunnel, and instrumentation temperatures constantly monitored for stability criteria - model reaches conditioned temperature before tunnel structure - can take several additional hours Operations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 23
Testing / Data Acquisition
Wind - on cost of cryogenic testing is elevated due to high power and liquid nitrogen cost Processes for acquisition focused on quality and efficiency to reduce consumables Key Tenets of Cryogenic Testing and Acquisition Wind - Off Zeroes - very important for high - quality force/moment data - frequency of wind - off zeroes dictated by thermal stability of balance and other instrumentation (can be configuration/condition dependent) - standard practice of acquiring zero data very close to thermal state of wind - on data Acquisition Duration - use of continuous sweep and active conditional sampling - optimized point - to - point model movement to reduce time on point - sharpened focus during wind - on testing, emphasis on reduced distractions and discussions while on condition Shorter Acquisition Times = Lower Nitrogen Usage = Lower Test Cost Operations [ Integrate unique European facility acquisition procedures] AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 24
Testing / Data Acquisition, Continued
Key Tenets of Cryogenic Testing and Acquisition, Continued Thermal Stability of Test Section - temperature sensors located in the test section and other tunnel areas monitored to ensure freestream flow is thermally stable and uniform - may require additional settling time prior to acquisition Review of Test Data - due to focused nature of acquisition, test data computed after a run set is completed - must be reviewed by test engineer or other representative prior to delivery to the customer, ensure corrections and data are computed correctly Operations [ Integrate unique European facility acquisition procedures] AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 25
Test Matrix Sequencing
Longer duration of some cryogenic processes emphasizes proper sequence of test matrix elements Efficiency Guidelines for Test Matrix Sequencing Process - Oriented Changes - typical order of most efficient to least efficient process changes Mach number pressure changes at constant temperature temperature changes - most temperature/pressure changes should be done at lower Mach number to minimize nitrogen consumption Model Configuration Changes - model changes at deep cryogenic temperatures require longer warming and conditioning times - if possible, model changes should be staged at warmer temperatures many times this is not possible, but expectations should be set accordingly for repeated cryogenic model changes [Validate statements with European standard practice] Operations AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 26
Model Access
AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 27
Unique Nature of Cryogenic Model Access
Easy ingress/egress More complex ingress/egress Optimized for efficiency/production Optimized for moisture reduction Typical Wind Tunnels Cryogenic Wind Tunnels Key Takeaways for Cryogenic Model Accesses Process to make the model accessible takes additional time due to complexity of facilities and safety (nitrogen ) - different facility designs yield different access procedures and methods Model must be warmed up from cryogenic temperatures prior to work being completed Emphasis on moisture reduction - limit personnel presence around model - constant dry air purge around model - limit time required to complete a change Model Access AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 28
Model Access Procedures, ETW
- Include abbreviated outline of ETW model access process - Include sketches and/or sequential photos of process Model Access [Requires discussion with ETW] AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 29
Model Access Procedures, NTF
Ingress Process - secure nitrogen injection system - open tunnel and insert access housings - warm model and condition environment for personnel Egress Process - purge access housings of all moisture - retract access housings and close tunnel - re - condition tunnel for testing Model accesses can be more efficient and less complex during non - cryogenic tests (air mode) Model Access AVT - 328 RTC@ETW: Day 2, Lecture 4 NATA Unclassified+JPN Slide 30