AIAA 2006-3076 MHD · MHD Flow Control and Power Generation in Low-Temperature Supersonic Air Flows Munetake Nishihara, J. William Rich, Walter R. Lempert, and Igor V. Adamovich Dt

Nonequilibrium Thermodynamics Laboratories The Ohio State University

AIAA 2006-3076

MHD Flow Control and Power Generation in Low-Temperature Supersonic Air Flows

Munetake Nishihara, J. William Rich, Walter R. Lempert, and Igor V. Adamovich

D t f M h i l E i iDept. of Mechanical EngineeringThe Ohio State University

And

Sivaram Gogineni

Innovative Scientific Solution, Inc.Innovative Scientific Solution, Inc.

SupportNonequilibrium Thermodynamics Laboratories The Ohio State University

pp

AFOSR grant FA9550-05-1-0085

Phase I AFOSR SBIR with ISSI

MotivationNonequilibrium Thermodynamics Laboratories The Ohio State University

MHD boundary layer flow separation control in hypersonic inlets

N d l ti l l i t ti t l l t i l d ti it• Needs relatively low interaction parameter: low electrical conductivity, modest magnetic field, use of lightweight permanent magnets

• Full-scale boundary layers are ~10 cm thick: need to demonstrate MHD control of relatively large cross section area flows

MHD ti b d f h i hi lMHD power generation on board of hypersonic vehicles

• Mach number and stagnation temperatures are too high for a power turbine (M=6, T0~2,000 K): MHD may be the only feasible option0 y y p

Typical flow conditions i f i i iimply the use of low-temperature, nonequilibrium plasmas

Objectives


• Characterize MHD pulser-sustainer discharge plasma (discharge power, flow temperature rise, conductivity, Hall parameter, cathode fall)

• Isolate Lorentz force effect on core flow Mach number using static pressure measurements: flow acceleration / decelerationp

• Detect MHD power generation in unseeded and seeded low-temperature flows

• Determine range of applicability for on-board MHD power generation (with simulations of pulser –sustainer discharge in magnetic field)

MHD test section schematic


Static pressure port

Optical access window

Flow

down

up

Sustainer current

Static pressure port

DC electrode block

Pulsed electrode block

Optical fiber location and line of sight

Magnet pole

• Contoured nozzle• 12 cm long 4 cm x 2 cm test section

Flow

B

g p

west

• 12 cm long, 4 cm x 2 cm test section• Equipped with pressure ports and Pitot ports• Ceramic/copper pulsed and DC electrode blocks• Stagnation pressure P0=0.2-1.0 atm

east Static pressure port

Stagnation pressure P0 0.2 1.0 atm• Ionization: repetitively pulsed discharge

MHD wind tunnel (shown with CPT pulser)


CPT pulser: U=20 kV ν=50 kHz τ=20 30 nsecCPT pulser: U=20 kV, ν=50 kHz, τ=20-30 nsec

New FID pulser: U=10-40 kV, ν=100 kHz, τ= 3-5 nsec

• High ionization efficiency at high E/N• Excellent plasma stability (duty cycle ~ 1:1000)

Repetitively pulsed discharge (40 kHz rep rate)+ DC sustainer in M=4 air flow


+ DC sustainer in M=4 air flow

Voltage [kV]

10

20

Voltage [kV]Current [A]

Voltage

Current

-10

0

10 Current

-30

-20

10

VPEAK=13.2 kVIPEAK=31.3 A

Air, B=1.5 T-500 0 500 1000

Time [ns]

-40

30 PEAK 3 .3

,P0=1 atm, Ptest=13 torr, Umax=13 kV

Time [ns]

Plasma always remains uniform and stable for run times of several seconds

Pulse voltage and sustainer current in M=3 nitrogen flowP0=1/3 atm P =8 torr


P0 1/3 atm, Ptest 8 torr

5

10Voltage [kV]

25 μs

2.0Current [A]

0

5 25 μs

0.0

1.0

-10

-530 ns

-1.0

0 25 50 75Time [μs]

-150 25 50 75 100

Time [μs]

-2.0

Pulse energy 1-2 mJ

Time averaged pulsed discharge

 = 0.95 A (top curve) =0.86 A (bottom curve) g p g

power 80-120 W DC discharge power 1.4 kW

N2 second positive band (C3Πu→B3Πg) emission in M=3 nitrogen: Flow temperatures with and without 1 4 kW discharge


Intensit [arbitrar nits] Intensity [arbitrary units]

Flow temperatures with and without 1.4 kW discharge

1.0

1.2Intensity [arbitrary units]

UPS = 0 kV

UPS = 2 kV 1.0

1.2Intensity [arbitrary units]

Synthetic spectra

T = 180 K

T 260 K

0.6

0.8

0.6

0.8

T = 260 K

T = 100 K

0.2

0.4

0.2

0.4

397 398 399 400 401Wavelength [nm]

0.0397 398 399 400 401

Wavelength [nm]

0.0

g g [ ]

Line of sight averagedT=180±20 K for both cases

ΔT~10 K (~90% of discharge power frozen in N2 vibrations)

Effect of Lorentz force and Joule heat on pressure and Mach number: 1-D theory


on pressure and Mach number: 1-D theory

Lorentz force⎞⎛

AIBBjF zy ≅=

Lorentz force⎟⎟⎠

⎞⎜⎜⎝

⎛⋅

−−⋅

−⋅= Q

uF

Mpu

dxdu &

γγ 1

112

( )[ ] ( )⎭⎬⎫

⎩⎨⎧ ⋅

−+⋅+−−⋅

−= Q

aMFM

Mdxdp &111

11 22

γγh

IRUIEjQ PSyy

)( −⋅≅⋅= αα&

Joule heat

⎭⎩ aMdx 1 AhjQ yy

α : Effective Joule heating factor

~0.1 due to energy storage in N2vibrational modePressure and velocity changes

for two different Lorentz force directions

5~1)1(// 2 +−=± MuduPdP γ

%10P±Δ

∆u±/u ~ 2%

/± udu %10~P

±

Analytic expressions for pressure rise and effective Joule heat factor


and effective Joule heat factor

MHD interaction parameter

210−≈=LBj zyη

Effective loading parameter

4≈⋅

=⋅

=EEj

K yyy αα2 10∞

≈=uρ

η 4≈==uBuBj

Kzzy

( ) 2( ) LBjM

Mpp zyAR ⋅−

+−⋅≅Δ−Δ

1112 2

2γ

: Pressure change for l ti f +F

ApΔ

( ) LEja

MMpp

yy

RA

11

2

2

−−Δ+Δ

≅γ

α

accelerating force, +F

RpΔ : Pressure change for t di f F

( ) j yyγretarding force, -F

Momentum transfer from electrons to neutral flow:how significant is it?


how significant is it?

# f f lli i

Ey40nN eτν

# of momentum transfer collisions per neutral particle

φdrvFlow u

Neutral velocity change per collision

4.0~~N

N erescollcoll τν

,tan dr mvφ β= =

,dr mvsmv

Mmu drcoll /15~2~ ±±Δ β

tandrv

φ β= =B Neutral flow velocity change

smNuu collcoll /12~2 ⋅Δ=Δ ±

311e cm10n −= cm/s107v 6

dr ⋅= 5β =∆u±/u ~ 2%

7e 101Nn −⋅= 110

coll s105ν −⋅= μsec75τ res =∆u±/u 2%

Isolation of Lorentz force effect from Joule heating effect


Test sectionDecelerating force

jup

B

Bj

B

jwest east

downj

j

A l ti fFlow Accelerating force

j

Lorentz force: B j polarity dependent

Magnet pole

j

BB

jLorentz force: B, j polarity dependent

Joule heating: polarity independent

j

Static pressure measurements in M=3 dry air flows


Air, P0=250 torr, Ptest=8.7 torr

UPS=2 kV, R=0.5 kΩ, =1.2 A1.3

Normalized pressure

di f

Dry air: B=1.5 T, R=1.0 kΩ

Pulsed discharge duration 0.5 s1.2

Retarding force

B east, j down

B west, j up

11.0=Δ−Δ

ppp AR1.1

Accelerating force

B east, j up

B west, j downp

1.0

1-D MHD model prediction:

α=0.101.0 2.0 3.0i

0.9Pulser alone

Time [s]

Static pressure measurements in M=3 N2 flows


2

Nitrogen, P0=250 torr, Ptest=8.5 torr

UPS=2 kV, R=0.5 kΩ, =0.9 A1.3Normalized pressure

Nitrogen: B=1.5 T, R=0.5 kΩ

Pulsed discharge duration 0.5 s1.2

Retarding force

B east, j down

B west, j up

12.0=Δ−Δ pp AR

1.1

Accelerating force

B east, j up

B west, j downp

1.0

1-D MHD model prediction:

α=0.111.0 2.0 3.00.9

Pulser alone

Time [s]

M=3 room air flows:Comparable pressure rise but no Lorentz force effect


Comparable pressure rise but no Lorentz force effect

1 5

2.0Current [A]

Dry air, = 0.51 A

Room air, = 0.052 A

1.2Normalized pressure

Room air: B=1.5 T, R=0.5 kΩ

Retarding force, = 0.076 A

1.0

1.5

1.1

Accelerating force, = 0.094 A

0.0

0.51.0

0 25 50 75 100-0.5

1.0 2.0 3.00.9

Time [μs] Time [s]

OHOOHOe 2222 +→++ −Lower current due to rapid electron attachment:

Comparable flow heating due to rapid vibrational relaxation N2-H2O: α=0.40

Comparison with quasi-1-D theory


3.1

3.2Mach number

Joule heating factor

0

1.3Normalized pressure

Joule heating factor

0 1

2.9

3.0

α = 0

α = 0.11.2

α = 0.1

α = 0.05

α = 0.0

2 6

2.7

2.8

ΔM

1 0

1.1

2.4

2.5

2.6

2 0 1 0 0 0 1 0 2 00.9

1.0

Air

Nitrogen

-2.0 -1.0 0.0 1.0 2.0Current [A]

-2.0 -1.0 0.0 1.0 2.0Current [A]

Decelerating force Accelerating force ΔM±=-0.13 at I = ±1.0 A in air

Comparison with quasi-1-D theory (continued)What would it take to increase Mach number?


What would it take to increase Mach number?

0.15Normalized pressure difference ( ) LBj

MMpp zyAR ⋅−

+−⋅≅Δ−Δ

1112 2

2γ

0.10

Very good agreement with experiment

0 05 Nitrogen0.05 Nitrogen

Dry air

Eq. (9)

Eqs. (2-5)

)1.0(4 =≈⋅

=⋅

= ααα

uBE

uBjEj

Kz

y

zy

yyeff

0.0 0.5 1.0 1.5Current [A]

0.00q ( )

True flow acceleration (Keff~1) would require increasing conductivity by arequire increasing conductivity by a

factor of 4 (up to σ=0.3 mho/m)

Cathode voltage fall vs. MHD e.m.f. (open voltage):Power generation show stopper


V lt [V]

Power generation show stopper

A A β 1 8

20

30

40Voltage [V]

B = +1.5 T0.8

1.0Average current, A

Nitrogen

B=0T

B=0.75T

β=1.8

β=1.2

0

10

20

B = 0 T0.6

B=1.5T

σ=0.073mho/m

β

-30

-20

-10

B = -1.5 T0.2

0.4

0 10 20 30Time [μs]

-40

-30

0 500 1000 1500Voltage, V

0.0

Uc= 250-500 V (increasing with B field)

Uopen= uBh = 25-30V (independent of σ)

g ,

Red flag: Cathode layer not self-sustained in power generation regime

Cathode layer bottleneckNonequilibrium Thermodynamics Laboratories The Ohio State University

y

Self sustaining criterion:0.4

Current [A]

)/11ln( γα +=dSelf-sustaining criterion:Pulse rep. rate: 100 kHz

0.2 Uopen<<Uc (αd<<1), γ<<1Low secondary emission from cathode

0.0

UPS= 500 V, = 0.17 A

Low secondary emission from cathode

Secondary electrons emitted from cathode do not multiply

0 4

-0.2 UPS= 300 V, = 0.10 A

UPS= 200 V, = 28 mA

UPS= 100 V, = 8.8 mANot a problem in high-temperature

MHD: thermionic emission0 10 20 30

Time [μs]

-0.4

E l l MHD ( A)

MHD: thermionic emission

Extremely low MHD currents (~mA)

at relatively high conductivity (σ>0.07-0.08 mho/m)

Pulser-sustainer discharge modeling calculations: kinetic model validation


calculations: kinetic model validation

0.8Current [A]

Experiment

Calculation

0.8Current [A]

0 4

0.6Calculation

0 4

0.6

0.2

0.4

0.2

0.4

Exp. <V> = 480 V

0 200 400 600 8000.0

0 50 100 1500.0

Exp. <V> = 530 V

Calc. <V> = 530 V

Voltage [V] Time [μs]

2-D time-dependent pulser-sustainer MHD discharge model

Reasonably good agreement with experiment → can be used for design study calculations

MHD discharge modeling calculations: power generation parametric design study (B=0)


generation parametric design study (B 0)

B=0, U=50 V

No field penetration into plasma

Extremely low current (0.52 mA)

Current w/o cathode layer bottleneck: 83 mA

Adding up to 0.1% seed(varying α) and/orusing high-emissionelectrodes (varyingγ=0.01-1.0) do not helpγ 0.01 1.0) do not help

MHD discharge modeling calculations: power generation parametric design study (B=1 5 T)


generation parametric design study (B 1.5 T)

B=1.5 T, U=50 V

No field penetration into plasma

Current circles around plasma

Extremely low current (0.26 mA)

Adding up to 0.1% seed(varying α) and/orusing high-emissionl t d ( ielectrodes (varyingγ=0.01-1.0) do not help

Is there a way out?

Pulser sustainer discharge at higher voltage (B=0 T)


B=0 T U=530 VB 0 T, U 530 V

Greater field penetration into plasma

Much higher current at the same conductivity (0.43 A)

Pulser-sustainer discharge at higher voltage (B=1.5 T)


B=1.5 T, U=530 V,

Very weak field penetration into plasma

Extremely low current (4 5 mA)Extremely low current (4.5 mA)

Increasing MHD open voltage: three options


Uopen= uBh (h=4 cm) Uopen/Uc~0.1

Increasing flow velocity: T0~u2 too low (300 K)

Increasing B field: both Uopen and Uc increase with B

Increasing MHD electrode separation: can this work?Increasing MHD electrode separation: can this work?

Proposed solution: scale up electrode separation h, run generator in Hall mode (Uopen= β·uBh, β=2-3)

SummaryNonequilibrium Thermodynamics Laboratories The Ohio State University

y

Stable high-power MHD pulser/sustainer discharge operation (up to 1.5 kW)

Static pressure measurements:

Diff i t ti i b l ti d t di L t•Difference in static pressure rises by accelerating and retarding Lorentz forces

•Comparison with 1-D MHD flow model: Good quantitative agreement

•First experimental evidence of MHD deceleration of cold M=3 nitrogen and air core flows

L t t MHD ti i t / d liLow-temperature MHD power generation experiments / modeling:

• Low open voltages reduce MHD current by more than two orders of magnitude (cathode layer bottleneck)g y

• This effect cannot be reduced by seeding the flow or by using electrodes with high secondary emission coefficient (γ~1)

• Need to increase MHD e.m.f. (open voltage) by at least an order of magnitude

Documents

AIAA 2006-3076 MHD · MHD Flow Control and Power Generation in Low-Temperature Supersonic Air Flows Munetake Nishihara, J. William Rich, Walter R. Lempert, and Igor V. Adamovich Dt