ENCL 8 2020 FRD Idle Plume Decay Supplement Rev 2.pdf

PLUME CENTERLINE PROFILE FOR IDLE (ETR = 10) AND THROTTLE BUMP (ETR = 15)

Egbert Hood, External Environment Lead , Aerodynamics and CFD

FRD IDLE ENGINE EXHAUST PLUME SUPPLEMENT

Rev- 2

Date: 26 02 2020

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• PURPOSE: Support development of criteria for parking separation and ramp design

• BACKGROUND:

– Legacy fighter jets have parking separation distances of 100 feet to 125 feet (per UFC 2-000-05N)

– Multiple concerns if minimum distance is extended to 200 feet

• “Navy/MC air stations will need to expand ramps to essentially the same size as those for cargo jets”

• Hanger retrofits will be required in ramp redesigns

• Space is just not available at some site to achieve this parking separation distances

• “…program cost for this space increase is significant”

• Supplemental Idle Plume Development Criteria

– Tropical Day (89.8 deg. F)

– Idle (ETR = 10) and Throttle Bump (ETR = 12 to 15) engine thrust settings

– Centerline plume temperatures discernable down to 10 deg. F increments

– Plume information out to approximately 200 feet

DATA REQUEST

Distance of interest for airfield ramp operations is between 100 feet and 200 feet behind the aircraft

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• Engine Plume Differences Between F-35 Variants (A, B and C) Not Significant in this Application

• Ambient Conditions

– Tropical Day (89.8 deg. F) at Sea Level (14.7 psi)

– Calibrated Airspeed, KCAS (0 knots)

• Engine Throttle Settings

– Idle, ETR = 10

• Engine Setting Used During Typical Surface Operations

– Idle, ETR = 15

• Brief Throttle Increase (Throttle Bump) Generally Used to Initiate Ground Roll for Taxiing

• Exhaust Centerline Variations Due to the Influence of Calm Ambient Conditions (~6 knots)

– Excess Temperature Range: 35 to 5* deg. F

– Velocity Range: 35 to 10* knots

– Influence of ambient conditions observed at plume temperatures below 35 deg. F and plume velocities below ~35 knots

F-35 PLUME MODEL DEVELOPMENT DETAILS

*Note: Exhaust plume indistinguishable from ambient winds below 5 deg. F and 10 knots

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Exhaust Excess Temp. = Plume Temp. – Ambient Temp.

Idle Plume Model Results (ETR = 10)

• Plume model centerline excess temperatures (black dotted line) align well with existing Hazard Zone plume profiles (solid red line) out to approximately 115 feet where plume is 50 degrees Fahrenheit above ambient conditions

• Idle plume model excess temperatures were verified to distances within the parking apron distances of interest (100- 200 feet)

• Ambient airfield conditions revealed the potential variation (hashed area) of centerline excess temperatures at Idle plume distances beyond ~150 feet as the plume temperature cools down to near the ambient temperatures

• Actual plume temperatures become difficult to discern from ambient conditions beyond ~220 feet

Throttle Bump Plume Model Results (ETR = 15)

• Plume model centerline excess temperatures (black dashed lines) show the Throttle Bump plume excess temperature increase versus the Idle plume profiles (solid red and black dotted lines)

• Throttle Bump plume model excess temperature increase has been verified to confirm the increase in plume core length

• Following the Idle plume results, ambient airfield conditions are expected to have a similar impact on the variation of centerline excess temperature values as the plume temperatures cool to near the ambient temperatures

– These excess temperature variations are not expected within the 100 to 200 foot airfield distance of interest

– Throttle bump model indicates centerline temperature variations around 235 feet

IDLE (ETR = 10) AND THROTTLE BUMP (ETR = 15) EXHAUST EXCESS TEMPERATURE

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IDLE (ETR = 10) AND THROTTLE BUMP (ETR = 15) EXHAUST VELOCITY

Personnel Hazard Velocity Criteria

• 35 mph = 51.33 FPS

Idle Plume Model Results (ETR = 10)

• Plume model centerline velocity (black dotted lines) align well with existing Hazard Zone plume profiles (solid red line) out to approximately 95 feet where plume centerline speed is 50 FPS (34.1 mph)

• Idle plume model velocities verified at distances within the parking apron distances of interest (100-200 feet)

• Calm airfield winds revealed the potential variation of centerline velocity (hashed area) at Idle plume distances beyond ~125 feet as the plume velocity slows to near the ambient wind speeds

• Actual Idle plume velocities become difficult to discern from ambient conditions beyond ~180 feet

Throttle Bump Plume Model Results (ETR = 15)

• Plume model centerline velocity (dashed black lines) show the Throttle Bump plume velocity increase versus the Idle Hazard Zone plume profiles (solid red and black dotted lines)

• Throttle Bump plume model velocity increase has been verified to confirm the increase in plume core length

• Following the Idle plume results, calm airfield winds are expected to have a similar impact on the variation of centerline velocities within the hashed area (beyond 205 feet), as the plume velocity slows to near the ambient wind speeds

– These velocity variations are only expected to occur beyond the 200 foot maximum range of the airfield distance of interest

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• FRD Idle Engine Exhaust Plume didn’t provide sufficient information for evaluation of traditional parking separation distances of 100 to 200 feet

– FRD Figure 1-38 plume data limited to 64 feet and 51 feet for the excess temperature and velocity, respectively.

– Idle ETR and Throttle Bump (ETR=12-15) settings with temperatures increments of 10 deg. F requested in an update to the plume centerline profile

• Tropical day type with calm ambient winds selected for plume model development

– Excess temperature and velocity chart with plume distances out to 220 feet developed for ETR=10 and ETR=15

– Figure 1-38 Idle centerline plume profile included in all charts for reference

– Variations in the centerline exhaust profiles provided to highlight the distances where calm ambient conditions are expected to impact the plume profile model

CONCLUSION

These supplemental Idle and Throttle Bump plume profiles should be sufficient for preliminary determination of personnel hazards due to F-35 engine operations on parking ramps