Driver, Dave

Hartman, Grover J.

Hui, Frank

Noyes, Eric

Philippidis, Daniel

Terrazas-Salinas, Imelda

NASA Technical Reports Server

NASA Ames Research Center – Entry Systems Technology Division
Moffett Field, CA
Evidence of Standing Waves in Arc Jet Nozzle Flow
Dave Driver, Joe Hartman, Daniel Philippidis, Eric Noyes, Frank Hui, Imelda Terrazas-Salinas
DMD-1
Examples of Waves from small disturbance on nozzle walls (supersonic flow)
Prandtl – Slight Roughness on Walls
AEDC – strips of tape on floor & ceiling
Amann (1971) – waves generated by throat section 
AIAA 2017 Aviation Forum Denver CO, 5-9 June 2017
M=1.5
Prabhu (AIAA2009-4080) CFD of waves in Arc Jet Nozzle
https://ntrs.nasa.gov/search.jsp?R=20170011255 2019-08-31T01:22:47+00:00Z
NASA Ames Arc Jet Facility
Arc Jet Schematic
• Flow is heated by an Electrical Arc 
• Super heated flow is accelerated through a converging/diverging nozzle to M>4
• Arc jet provides a realistic atmospheric entry environment for testing heat shield material
• High Enthalpy
• Aerodynamic and Thermal Loads
• Arc Jet  testing is a key part of  Thermal Protection Systems development / qualification
• Nozzle exit diameter can be varied from 152 mm to 1041 mm by adding nozzle segments
• The 152 mm (6”) and 330mm (13”) nozzles are popular – customers wanted a 229mm (9”)
Test
Article
CFD Simulation of Arc Jet Flow
DMD-2
X’(m)
x(mm)
Test Box 
Under Vacuum
Outline
New IHF 9” Nozzle Checkout
– New 9” (229mm) exit diameter nozzle for the Interactive Heating Facility (IHF) 
intermediate nozzle (between 6” and 13”) designed to facilitate adding
radiative heating to a wedge test article (with new 100KW laser)
– Initial checkout of the nozzle using stagnation test articles
– Teflon “Burn” patterns
– Radial Sweeps with Pressure and Heat Flux Probes
– Instrumentation study with spectral emission and Laser Induced Fluorescence
In the process of Checkout
– Non-uniform burn patterns on Teflon test articles (at x=127mm and 178mm)
– Experimentally Observed standing waves in the IHF nozzle
– CFD with real gas effects ( follow up to Dinesh Prabhu AIAA 2009-4080)
– Simulation of test articles
– Proposal for Alternate Nozzle Design (wave free)
Acknowledgement
This work was partially funded under the NASA Strategic Capabilities Assets Program (SCAP) 
and the Laser-Enhanced Arc Jet Facilty (LEAF) programs.
DMD-3
New IHF 9” Nozzle Check Out
Features
– Extension of IHF 6” (152mm) nozzle throat section
– Special attention to joint between IHF throat section and 9” (229mm) Extension
– Longer Plenum Chamber produces flatter enthalpy distribution (not discussed here)
– Desire better flow quality than was had with the IHF 8” (203mm)  nozzle extension
IHF 9” Nozzle with Long Plenum Chamber
DMD-4
New Longer Plenum
X’(m)
x(mm)
9” Nozzle Check Out Test Plan
Range of Test Condition – spanning the test envelope
Test Conditions _Probe at x=76mm_
Case Current Voltage Main Air Add Air Argon Pplenum Pstag q4”Hemi Hsonic
# amps Volts gm/s gm/s gm/s kPa kPa W/cm2 MJ/kg
CEV-a13 3450 2720 105 645 51 350 30.7  92 2.9 
MSL-a1 3500 4795 330 551 59 593 52.3  350 7.2
MSL-c1 2000 3430 200 55 21 180 19.8 375 7.8
MSL-c4 3500 5910 546 55 42 555 52.0 706 15.6
MSL-c8 6000 6600 741 55 54 810 75.9 995 24.4 
IsoQ Teflon Test Article Recession
Pre-Test          Post Test
DMD-5
Fast Response Probes (Null Pt  & CoaxTC)
• IsoQ produces uniform heating across its face
• Teflon recession is proportional to heat rate
• Teflon “Burns” give global map of heat flux
• Asses uniformity of heating (aka flow quality)
Radial Sweeps of Multiple Types of Heat Flux Sensors 
DMD-6
Gardon Gage Coax TCNull Point
Fast Response Sensors (Null Point, CoaxTC,Gardon Gage)
• Coax,NullPt & Gardon give similar shaped radial distribution of heat flux
Gardon Gage calibration adjusted to match Coax TC measurement
• Pressure measured with same probe as heat flux (orifice slightly off center)
• Relatively uniform distribution of Enthalpy (Enthalpy deduced from Fay-Riddell)
MSL-C4  x=76mm
4” Hemi with 
Pressure tap
Radial Distance From Jet Centerline (inches) 
Teflon Burns as a function of Condition
c1 c4 c8 a1 a13
• Teflon Burns done at 76mm (x=3”) downstream of nozzle exit
• All Teflon was initially 4” IsoQ
• IsoQ shape preserved in most cases.
• C8 condition produced a little flatness in the center of the face
• Flow quality deemed to be good at x= 76mm
• However problems were discovered at downstream locations
DMD-7
Teflon Burns as a function of distance from 
the nozzle exit plane (at condition c4) 
x=1” x=3” x=5” x=7” x=9”
Initial Shape IsoQ
x=25mm          x=76mm           x=127mm         x=178mm
Initial Shape Flat Face
x=25mm                                                      x=178mm         x=229mm
DMD-8
Non-Uniform Burn patterns at x=127mm and 178m – why?
Radial Distribution of Stagnation Pressure at various x
Local minimum in pressure seen upstream of x=127mm
Local maximum in pressure seen downstream of x=127mm
At MSL-c4 i=3500amps, mmain/madd/mAr = 546, 55, 54 gm/s
DMD-9
x=25mm
x=76mm
x=127mm
x=178 mm
x=229mm
.Width of Pressure Disturbance vs Axial Position
There appears to be a conical wave 
converging at   x ~ 127mm
What is the source of the wave?
DMD-10
Characteristic Lines (CFD) emanating from nozzle throat look similar
Waves Seen in CFD done by Prabhu (AIAA 2009-4080)
Waves spawned 
from discontinuity 
in curvature
DMD-11
Nozzle Simulation of Existing IHF Throat
Constant Curvature followed by Abrupt change to zero Curvature
Compression waves spawned from Abrupt change in curvature
2nd Wave Intersection 
DMD-12
2ndWave Intersection – Effect on Pressure
• There is a local minimum in pressure on the centerline of the flow 
ahead of the wave intersection point and a local maximum downstream 
– similar to what is seen in experimentally.
• What can be done to eliminate this wave?
 Eliminate the discontinuity in curvature at the nozzle throat
DMD-13
Eric Noyes Proposed IHF Throat (cubic spline)
DMD-14
Smooth Decrease in Curvature down to zero
Absence of Compression waves – no local minimum in Pitot Pressure
Other Possible Source of Waves – Joint
•Nozzle Joint discontinuity due to slope difference associated with 
tolerance stack up  (+/- 0.03
o
)  a hypothetical scenario
•Is this significant enough to cause waves
Discontinuity 
in Curvature
Discontinuity 
in Slope 
13”
Nozzle Joint 
Discontinuity
9.978º
Hypothetical Case (sensitivity to slope discontinuity)
DMD-15
10.009º
Discontinuity in Slope at Joint
•.Waves from both Curvature discontinuity and difference in slope at joint
DMD-16
Stagnation Heat Flux on IsoQ Test Articles
DMD-17
x
 
=
 
 
 
2
5
m
m
x
 
=
 
 
 
7
6
m
m
x
 
=
 
1
2
7
m
m
x
 
=
 
1
7
9
m
m
x
 
=
 
2
2
9
m
m
Local Minimum in 
heating when model 
is at the x=127mm 
location.  Consistent 
with Teflon Burn
This is consistent 
with Teflon’s low 
recession rate
Stagnation Heat Flux on IsoQ vs x
DMD-18
x
 
=
 
-
1
2
7
m
m
x
 
=
 
-
5
1
 
m
m
x
 
=
 
-
2
5
 
m
m
x
 
=
 
7
6
m
m
x
 
=
 
1
2
7
m
m
x
 
=
 
1
7
9
m
m
x
 
=
 
2
2
9
m
m
Local Minimum in 
heating when model 
is at the x=127mm 
location.  Consistent 
with Teflon Burn
This is consistent 
with Teflon’s low 
recession rate
Stagnation Heat Flux on Flat Faced Test Articles
DMD-19
x
 
=
 
 
 
2
5
m
m
x
 
=
 
 
 
7
6
m
m
x
 
=
 
1
2
7
m
m
x
 
=
 
1
7
9
m
m
x
 
=
 
2
2
9
m
m
Local Maximum in 
heating when model 
is at the x=179mm 
location.  Consistent 
with Teflon Burn.
This is consistent 
with Teflon’s high 
recession rate
Summary
•Waves are seen experimentally in radial pressure distributions (waves intersect at x=127mm).
•Teflon test articles show non-uniform recession when test articles are placed near x=127mm.
•CFD indicates that waves can be expected from a discontinuity in curvature at the throat.
(although relatively week)
•CFD shows that small discontinuities in nozzle slope (across a joint) can cause significant waves
•CFD predicts a non-uniformity in heating on test articles placed near x=127mm.
•Waves can be an issue for the new 229mm nozzle, and it is best to test upstream of x=76mm.
•Waves are a relative non-issue for the 152mm and 330mm nozzles, as their focal point is far 
from where models are tested
Future Nozzle design
•There is a plan to build a new throat section in which the discontinuity in curvature is eliminated.
•The as built nozzle segments will be measured and CFD performed on them.
•If a wave free 229mm nozzle is required, then it may be necessary to make it a single piece.
DMD-20
Backup
DMD-21
Radial Distributions for various conditions at x=76mm
Heat Flux  Distribution (Gardon Gage)                  Pressure Distribution
Condition MSL-c1,”c2”, c4, c8
• Local disturbance seen in pressure and heat flux near centerline (at 
x=76mm location) for most conditions
• Recall Teflon looked reasonably good at x=76mm
• Disturbance broadening with reduction in flow enthalpy
i.e., wave intersection point moving downstream as flow approaches ideal gas
DMD-22
.Pressure measured by Probes of Different Size
DMD-23
• Pressure measured by 102mm Hemi and 9 mm Sphere Cone agree
.Heat Flux Measured by Probes of Different Size
DMD-24
• Magnitude of qcw sqrt(R) measured by 102mm Hemi and 13mm Sphere Cone agree
• But the smaller probe does not measure local extrems in heating
qcw sqrt(13mm/102mm)
Effect on Teflon IsoQ Test Articles
DMD-25
x
 
=
 
-
1
2
7
m
m
x
 
=
 
-
5
1
 
m
m
x
 
=
 
-
2
5
 
m
m
x
 
=
 
7
6
m
m
x
 
=
 
1
2
7
m
m
x
 
=
 
1
7
9
m
m
x
 
=
 
2
2
9
m
m
Local Minimum in 
heating when model 
is at the x=127mm 
location.  Consistent 
with Teflon Burn
This is consistent 
with Teflon’s low 
recession rate
Photo of 9” nozzle after testing 
No gap between throat and 9” extension
8” Nozzle extension had a gap (step?)
A couple of small streaks at 6 o’clock position
Associated with small steps 
9” Nozzle
DMD-26


Evidence of Standing Waves in Arc Jet Nozzle Flow

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