AerE 344 class notes - Iowa State Universityhuhui/teaching/2014Fx/class... · measuring velocity...

Copyright Copyright ©© by Dr. Hui Hu @ Iowa State University. All Rights Reserved!by Dr. Hui Hu @ Iowa State University. All Rights Reserved!

HHui Huui HuDepartment of Aerospace Engineering, Iowa State University Department of Aerospace Engineering, Iowa State University

Ames, Iowa 50011, U.S.AAmes, Iowa 50011, U.S.A

Lecture # 04 Pressure MeasurementLecture # 04 Pressure Measurement Techniques Techniques and and InstrumentationInstrumentation

AerEAerE 34344 class notes4 class notes


Measurement Techniques for ThermalMeasurement Techniques for Thermal--Fluids StudiesFluids Studies

ThermalThermal--Fluids Fluids measurementmeasurementtechniquestechniques

Intrusive Intrusive techniquestechniques

NonNon--intrusiveintrusivetechniquestechniques

•• PitotPitot probeprobe•• hotwire, hot filmhotwire, hot film•• thermocouplesthermocouples•• etc ...etc ...

•• Laser Doppler Laser Doppler VelocimetryVelocimetry (LDV)(LDV)•• Planar Doppler Planar Doppler VelocimetryVelocimetry (PDV)(PDV)•• Particle Image Particle Image VelocimetryVelocimetry (PIV)(PIV)•• etcetc……

particleparticle--based based techniquestechniques

•• Laser Induced Fluorescence (LIF)Laser Induced Fluorescence (LIF)•• Molecular Tagging Molecular Tagging VelocimetryVelocimetry (MTV)(MTV)•• Molecular Tagging Molecular Tagging TherometryTherometry (MTT)(MTT)•• Pressure Sensitive Paint (PSP)Pressure Sensitive Paint (PSP)•• Temperature Sensitive Paint (TSP)Temperature Sensitive Paint (TSP)•• Quantum Dot ImagingQuantum Dot Imaging•• etc etc ……

moleculemolecule--based based techniquestechniques

Velocity, temperature, density (concentration), etc..


Pressure measurements

• Pressure is defined as the amount of force that presses on a certain area. – The pressure on the surface will increase if you make the force on an area bigger. – Making the area smaller and keeping the force the same also increase the pressure.– Pressure is a scalar

dAdF

AFP nn ==

dA

ndF

τ̂

n̂


Pressure measurements

ambabsolutegauge PPP −=

Manometer


Mechanical Pressure Gauges Mechanical Pressure Gauges --11

Fluid chamberFluid chamber

weightweight

pumppump

cylindercylinderplungerplunger

Calibration Calibration pressurepressure

PP

Deadweight gauges:• High accuracy

• Usually used for the calibration of other instruments

• Application range : 102~108 pa

•Uncertainty is within 0.01% ~0.05% of the reading


Mechanical Pressure Gauges Mechanical Pressure Gauges --22

ElasticElastic--element gauges:element gauges:

•• Contain an elastic elements that deforms under pressure and Contain an elastic elements that deforms under pressure and creates a linear or angular displacementcreates a linear or angular displacement

•• The displacement is either displayed on a dial by means of The displacement is either displayed on a dial by means of purely mechanical linkages or transformed to an electric signal purely mechanical linkages or transformed to an electric signal that can be displayed or recorder at will.that can be displayed or recorder at will.

•• They usually used for monitoring supply pressureThey usually used for monitoring supply pressurep

p

p

Cross sectional shape Curved Bourdon tube

Twisted Bourdon tube


Electrical Pressure transducersElectrical Pressure transducers

•• These devices provides an electric output signal that is These devices provides an electric output signal that is linearly or nonlinearly dependent on the absolute pressure or linearly or nonlinearly dependent on the absolute pressure or a pressure difference.a pressure difference.

•• They can be categorized as:They can be categorized as:–– Molecular transducers: Molecular transducers:

•• Applied pressure or force produces a change (on the Applied pressure or force produces a change (on the molecular level) of a electrical property of material.molecular level) of a electrical property of material.

•• PiezoPiezo--electric material such as quartz crystal: change electric material such as quartz crystal: change in internal dipole moments of the molecules of the in internal dipole moments of the molecules of the crystal when the pressure or force is applied.crystal when the pressure or force is applied.

–– Parametrical transducers:Parametrical transducers:•• The gross electrical parameter (resistance, The gross electrical parameter (resistance,

inductance, capacitance) of an associate electrical inductance, capacitance) of an associate electrical parameter is altered by applied force.parameter is altered by applied force.

•• VariableVariable--capacitance transducercapacitance transducer p

E


Wall Pressure measurements Wall Pressure measurements --11

•• Making small orifice (pressure tap) facing the flow.Making small orifice (pressure tap) facing the flow.

•• Machining small hole could be difficultMachining small hole could be difficult•• d = 0.5~3.0mm in practiced = 0.5~3.0mm in practice•• l/dl/d = 5 ~ 15 is common used= 5 ~ 15 is common used

•• Potential effect on the wall roughnessPotential effect on the wall roughness•• Effects of unsteady shock wave, and shockEffects of unsteady shock wave, and shock--

boundaryboundary--layer interactions for transonic and layer interactions for transonic and supersonic flows:supersonic flows:

•• PSP method to be introduced laterPSP method to be introduced later

V, P

PPmm

ll

dd

0>−=Δ PPp m


Wall Pressure measurements Wall Pressure measurements -- 22

•• For a unsteady flow, the dynamic response of a For a unsteady flow, the dynamic response of a pressure acquisition system is a key issue!pressure acquisition system is a key issue!

–– Dynamic response of the pressure transducersDynamic response of the pressure transducers–– Dynamic response of the connection tubingDynamic response of the connection tubing

•• Remote connectionRemote connection–– Dynamic response is lowDynamic response is low–– Spatial resolution is highSpatial resolution is high

•• Cavity mountingCavity mounting–– Dynamic response is goodDynamic response is good–– Spatial resolution is highSpatial resolution is high

•• Flush mountingFlush mounting–– Dynamic response is highDynamic response is high–– Spatial resolution is lowSpatial resolution is low

Pressure Pressure transducerstransducers

VV

Connection Connection tubingtubing

pressure pressure transducertransducer

VV

VV

pressure pressure transducertransducer


Pressure Measurements inside Flow FieldPressure Measurements inside Flow Field

•• NonNon--intrusive technique is unavailable for direct intrusive technique is unavailable for direct pressure measurementspressure measurements

–– Based on NBased on N--S equation to calculate pressure field using S equation to calculate pressure field using the measured (PIV) velocity field. the measured (PIV) velocity field.

•• Static probe: for static pressure measurementsStatic probe: for static pressure measurements•• PitotPitot probe: for total pressure measurementsprobe: for total pressure measurements•• PitotPitot--static probe: for static and total pressures static probe: for static and total pressures

measurements (velocity measurements)measurements (velocity measurements)•• MultiMulti--hole probe:hole probe:


Pressure Sensitive Paint (PSP) techniquePressure Sensitive Paint (PSP) technique

•• Composition of Air: 78.08% NComposition of Air: 78.08% N22, 20.95% O, 20.95% O22, 0.93% , 0.93% ArAr, 0.03% CO, 0.03% CO22, 0.002% Ne, plus , 0.002% Ne, plus lesser amounts of Methane, Helium, Krypton, Hydrogen, Xenon.lesser amounts of Methane, Helium, Krypton, Hydrogen, Xenon.

•• The pressure of air can be determined if the particle pressure oThe pressure of air can be determined if the particle pressure of oxygen (i.e. oxygen f oxygen (i.e. oxygen concentration) can be measured. concentration) can be measured.

•• A typical pressure sensitive paint is comprised of two main partA typical pressure sensitive paint is comprised of two main parts: an oxygen sensitive s: an oxygen sensitive fluorescent molecule and an oxygen permeable binderfluorescent molecule and an oxygen permeable binder


Applications of PSP TechniqueApplications of PSP Technique

PSP combined with PIVPSP combined with PIV

PSP measurement resultPSP measurement result


Applications of PSP TechniqueApplications of PSP Technique


PSP Technique for Low Speed ApplicationsPSP Technique for Low Speed Applications

PSP measurements of PSP measurements of a 2002 Ford Thunderbirda 2002 Ford Thunderbird

VV∞∞=50m/s=50m/s


AerE34AerE3444 Lab #Lab #0303: Pressure Sensor Calibration and: Pressure Sensor Calibration andMeasurement Uncertainty AnalysisMeasurement Uncertainty Analysis

•• Task #1: Task #1: Pressure Sensor Calibration experimentPressure Sensor Calibration experiment–– A pressure sensor A pressure sensor –– SetraSetra pressure transducer with a range of +/pressure transducer with a range of +/-- 5 inH2O5 inH2O

•• It has two pressure ports: one for total pressure and one for sIt has two pressure ports: one for total pressure and one for static (or reference) pressure.tatic (or reference) pressure.

–– A computer data acquisition system to measure the output voltageA computer data acquisition system to measure the output voltage from the manometer.from the manometer.–– A manometer of known accuracy A manometer of known accuracy

•• MensorMensor Digital Pressure Gage, Model 2101, Range of +/Digital Pressure Gage, Model 2101, Range of +/-- 10 inH2O10 inH2O

–– A plenum and a hand pump to pressurize it. A plenum and a hand pump to pressurize it. –– Tubing to connect pressure sensors and plenumTubing to connect pressure sensors and plenum

•• Lab output:Lab output:–– Calibration curve Calibration curve –– Repeatability of your resultsRepeatability of your results–– Uncertainty of your measurementsUncertainty of your measurements

SetraSetra pressure pressure transducertransducer

(to be calibrated)(to be calibrated)

MensorMensor Digital Digital Pressure GagePressure Gage A computerA computer A plenumA plenum hand pumphand pump

tubingtubing


Calibration curves

0

200

400

600

800

1000

1200

1400

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Experimental datacurve fitting

y=a+bx max dev:30.4, r2=0.998a=13.2, b=240

Voltage (V)

Pre

ssur

e (P

a)


•• Task #2: velocity profile measurements of Task #2: velocity profile measurements of a Wa Wind ind tunneltunnel

–– A A SetraSetra manometer to be used with a manometer to be used with a PitotPitot--static probe.static probe.

–– A A PitotPitot--static probe mounted to a traverse for static probe mounted to a traverse for measuring velocity profiles in the wind tunnel.measuring velocity profiles in the wind tunnel.

–– A thermometer and barometer for observing A thermometer and barometer for observing ambient lab conditions (for calculating ambient lab conditions (for calculating atmospheric density).atmospheric density).

–– A computer with a data acquisition system A computer with a data acquisition system capable of measuring the voltage from your capable of measuring the voltage from your pressure transducer.pressure transducer.

•• Lab OutputLab Output–– Velocity profiles across the wind tunnel test Velocity profiles across the wind tunnel test

section.section.

AerE34AerE3444 Lab #Lab #0303: Pressure Sensor Calibration and: Pressure Sensor Calibration andMeasurement Uncertainty AnalysisMeasurement Uncertainty Analysis

b. Flat plateb. Flat plate

a. streamlined airfoila. streamlined airfoil

ρ

ρ

)(2

)(,21

0

20

stat

stat

ppV

BernoulliVpp

−=

+=


Velocity profile in the Bill James wind Tunnel

0

2

4

6

8

10

12

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Position (mm)

Vel

ocity

(m/s

)

AerE 344 class notes - Iowa State Universityhuhui/teaching/2014Fx/class... · measuring velocity...

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