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Review on the sensed temperature in cold-wire and hot-wire anemometry
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0001-8127-8124
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0002-1663-3553
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0002-1146-3241
2010 (English)Report (Other academic)
Abstract [en]

Instantaneous velocity and temperature measurements by means of hot-wire and coldwires have become a standard technique used in almost every fluid dynamic research laboratory. Nonetheless, when it comes to compressible flows in applied fields, there seems to remain a need for clarification on which temperature is actually measured by a cold-wire and which temperature a hot-wire senses as its fluid temperature. The present paper reviews the view present in the literature and presents additional experimental evidence, that it is indeed the recovery temperature that is measured by a cold-wire and that this is also the temperature needed to compensate hot-wire readings in nonisothermal compressible flows

Place, publisher, year, edition, pages
2010. , 11 p.
Keyword [en]
hot-wire anemometry, cold-wire anemometry, recovery temperature, temperature
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-26343OAI: oai:DiVA.org:kth-26343DiVA: diva2:371877
Note
QC 20101208Available from: 2010-11-23 Created: 2010-11-23 Last updated: 2012-05-10Bibliographically approved
In thesis
1. Flow Measuring Techniques in Steady and Pulsating Compressible Flows
Open this publication in new window or tab >>Flow Measuring Techniques in Steady and Pulsating Compressible Flows
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with flow measuring techniques applied on steady and pulsatingflows. Specifically, it is focused on gas flows where density changes canbe significant, i.e. compressible flows. In such flows only the mass flow ratehas a significance and not the volume flow rate since the latter depends onthe pressure. The motivation for the present study is found in the use of flowmeters for various purposes in the gas exchange system for internal combustionengines. Applications can be found for instance regarding measurements of airflow to the engine, or measurements of the amount of exhaust gas recirculation.However the scope of thesis is wider than this, since the thesis aims toinvestigate the response of flow meters to pulsating flows. The study is mainlyexperimental, but it also includes an introduction and discussion of several inindustry, common flow measuring techniques.The flow meters were studied using a newly developed flow rig, designedfor measurement of steady and pulsating air flow of mass flow rates and pulsefrequencies typically found in the gas exchange system of cars and smallertrucks. Flow rates are up to about 200 g/s and pulsation frequencies from 0 Hz(i.e. steady flow) up to 80 Hz. The study included the following flow meters:hot-film mass flow meter, venturi flowmeter, Pitot tube, vortex flowmeter andturbine flowmeter. The performance of these meters were evaluated at bothsteady and pulsating conditions. Furthermore, the flow under both steady andpulsating conditions were characterized by means of a resistance-wire basedmass flow meter, with the ability to perform time resolved measurements ofboth the mass flux ρu, and the stagnation temperature T0.Experiments shows that, for certain flow meters, a quasi-steady assumptionis fairly well justified at pulsating flow conditions. This means that thefundamental equations describing the steady flow, for each instant of time,is applicable also in the pulsating flow. In the set-up, back-flow occurred atcertain pulse frequencies, which can result in highly inaccurate output fromcertain flow meters, depending on the measurement principle. For the purposeof finding means to determine when back flow prevails, LDV measurementswere also carried out. These measurements were compared with measurementsusing a vortex flow meter together with a new signal processing technique basedon wavelet analysis. The comparison showed that this technique may have apotential to measure pulsating flow rates accurately.Descriptors: Flow measuring, compressible flow, steady flow, pulsating flow,hot-wire anemometry, cold-wire anemometry.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. 89 p.
Series
Trita-MEK, ISSN 0348-467X ; 2010:09
Keyword
Flow measuring, compressible flow, steady flow, pulsating flow, hot-wire anemometry, cold-wire anemometry
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-26344 (URN)978-91-7415-824-3 (ISBN)
Presentation
2010-12-12, Sal S40, KTH, Teknikringen, Stockholm, 15:12
Opponent
Supervisors
Note
QC 20101208Available from: 2010-12-08 Created: 2010-11-23 Last updated: 2010-12-08Bibliographically approved
2. Flow measurements related to gas exchange applications
Open this publication in new window or tab >>Flow measurements related to gas exchange applications
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with flow measuring techniques applied to steady and pulsating gas flows relevant to gas exchange systems for internal combustion engines. Gas flows in such environments are complex, i.e. they are inhomogeneous, three-dimensional, unsteady, non-isothermal and exhibit significant density changes. While a variety of flow metering devices are available and have been devised for such flow conditions, the performance of these flow metersis to a large extent undocumented when a strongly pulsatile motion is superposed on the already complex flow field. Nonetheless, gas flow meters are commonly applied in such environments, e.g. in the measurement of the air flow to the engine or the amount of exhaust gas recirculation. The aim of the present thesis is therefore to understand and assess, and if possible to improve the performance of various flow meters under highly pulsatile conditions as well as demonstrating the use of a new type of flow meter for measurements of the pulsating mass flow upstream and downstream the turbine of a turbocharger.

The thesis can be subdivided into three parts. The first one assesses the flow quality of a newly developed flow rig, designed for measurements of steady and pulsating air flow at flow rates and pulse frequencies typically found in the gas exchange system of cars and smaller trucks. Flow rates and pulsation frequencies achieved and measured range up to about 200 g/s and 80 Hz, respectively. The time-resolved mass flux and stagnation temperature under both steady and pulsating conditions were characterized by means of a combined hot/cold-wire probe which is part of a newly developed automated measurement module. This rig and measurement module were used to create a unique data base with well-defined boundary conditions to be used for the validation of numerical simulations, but in particular, to assess the performance of various flow meters.

In the second part a novel vortex flow meter that can measure the timedependent flow rate using wavelet analysis has been invented, verified and extensively tested under various industrially relevant conditions. The newly developed technique was used to provide unique turbine maps under pulsatile conditions through time-resolved and simultaneous measurements of mass flow, temperature and pressure upstream and downstream the turbine. Results confirm that the quasi-steady assumption is invalid for the turbine considered as a whole.

In the third and last part of the thesis, two basic fundamental questions that arose during the course of hot/cold-wire measurements in the aforementioned high speed flows have been addressed, namely to assess which temperature a cold-wire measures or to which a hot-wire is exposed to in high speed flows as well as whether the hot-wire measures the product of velocity and density or total density. Hot/cold-wire measurements in a nozzle have been performed to test various hypothesis and results show that the recovery temperature as well as the product of velocity and stagnation density are measured.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. viii, 197 p.
Series
Trita-MEK, ISSN 0348-467X ; 2012:08
Keyword
Flow meters, vortex flow meters, compressible flow, pulsating flow, hot-wire anemometry, cold-wire anemometry, time resolved measurements, wavelet analysis
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-94133 (URN)978-91-7501-385-5 (ISBN)
Public defence
2012-06-01, E2, Lindstedtsvägen 3, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note
QC 20120510Available from: 2012-05-10 Created: 2012-05-07 Last updated: 2012-05-10Bibliographically approved

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