A simultaneous planar laser-induced fluorescence, particle image velocimetry and particle tracking velocimetry technique for the investigation of thin liquid-film flows

AbstractA simultaneous measurement technique based on planar laser-induced fluorescence imaging (PLIF) and particle image/tracking velocimetry (PIV/PTV) is described for the investigation of the hydrodynamic characteristics of harmonically excited liquid thin-film flows. The technique is applied as part of an extensive experimental campaign that covers four different Kapitza (Ka) number liquids, Reynolds (Re) numbers spanning the range 2.3–320, and inlet-forced/wave frequencies in the range 1–10Hz. Film thicknesses (from PLIF) for flat (viscous and unforced) films are compared to micrometer stage measurements and analytical predictions (Nusselt solution), with a resulting mean deviation being lower than the nominal resolution of the imaging setup (around 20μm). Relative deviations are calculated between PTV-derived interfacial and bulk velocities and analytical results, with mean values amounting to no more than 3.2% for both test cases. In addition, flow rates recovered using LIF/PTV (film thickness and velocity profile) data are compared to direct flowmeter readings. The mean relative deviation is found to be 1.6% for a total of six flat and nine wavy flows. The practice of wave/phase-locked flow-field averaging is also implemented, allowing the generation of highly localized velocity profile, bulk velocity and flow rate data along the wave topology. Based on this data, velocity profiles are extracted from 20 locations along the wave topology and compared to analytically derived ones based on local film thickness measurements and the Nusselt solution. Increasing the waviness by modulating the forcing frequency is found to result in lower absolute deviations between experiments and theoretical predictions ahead of the wave crests, and higher deviations behind the wave crests. At the wave crests, experimentally derived interfacial velocities are overestimated by nearly 100%. Finally, locally non-parabolic velocity profiles are identified ahead of the wave crests; a phenomenon potentially linked to the cross-stream velocity field

A Hybrid Numerical Method for 3D Multiphysics Modeling of Ultrasonic Transit-Time Flowmeters : Including Sound Propagation in Real Pipe Flows

Ultralyd mengdemålere av typen Ultrasonic Transit-Time Flowmeters (UTTF) og deres modellering er hovedfokus i denne avhandlingen. UTTF kan kategoriseres i clamp-on og inline-målere avhengig av behovene til applikasjoner for mengdemåling. Simuleringer, studier og eksperimentell verifisering av inline-målere med høye krav til nøyaktighet utføres i dette arbeidet. Det er demonstrert at ved bruk av simuleringer er det mulig å akselerere innovasjon, samt å kontinuerlig forbedre målenøyaktighet og teknologi for det raskt voksende markedet for UTTF. I denne avhandlingen foreslås en multifysikk, hybrid numerisk metode, dvs. en kombinasjon av en Finite Element Method (FEM) og en Finite Volume Method (FVM), for 3D-simuleringer og undersøkelse av fysiske fenomener som påvirker oppførselen til UTTF. Den utviklede metoden, ’Simulations of Piezoelectricity, Acoustics, Coupled with CFD’ (SimPAC2), brukes som et designverktøy for UTTF, samt for å forbedre forståelsen av virkemåten av UTTF. For simuleringen er UTTF delt inn i to deler, og den respektive, mer passende metoden brukes for hver del. Konkret brukes FEM for simulering av piezoelektrisitet og strukturell akustikk i de faste delene, dvs. transduserne og om ønskelig, delvis i målerøret. FEM brukes også til simulering av bølgeutbredelse i deler av mediet. Akustikk og simulasjoner ved Computational Fluid Dynamics (CFD) vurderes i mediet, samt deres interaksjon med hverandre ved bruk av FVM, som tradisjonelt er mer passende for CFD og store simuleringer som trenger sterk parallellisering. Den hybride SimPAC2-metoden krever komplekse grensesnitt mellom FEM- og FVM-metoden, som er utviklet i løpet av denne oppgaven. En sammenligning av SimPAC2-resultater med simuleringer basert på kun CFD og FEM, samt sjekket mot fysisk utførte målinger. En kjedeverifisering utføres, med utgangspunkt i en simulering av en enkel geometri av piezoelektriske elementer i luft uten strømning og i jevn strømning. Kompleksiteten økes med simuleringen av en diametral en-stråle mengdemåler utstyrt med enten piezo-elektriske elementer eller ekte transdusere. Til slutt ble en industriell mengdemåler med to kordale strålebaner simulert og verifisert i en kalibreringsrigg. Resultatene stemte overens innen fastsatte kriterier. Simuleringene gjorde det mulig å systematisk studere og kvantifisere komplekse, forventede effekter i UTTF, for eksempel 3D-hulromseffekter for flush monterte, tilbaketrekkende eller utstikkende transdusere. De utførte 3D-multifysikksimuleringene fanger opp interaksjoner mellom ultralydbølger og strømning i 3D-geometrien som per definisjon ikke kan fanges opp av 2D-simuleringer. Før SimPAC2 var det dyrt eller umulig å utføre systematiske 3D-multifysikksimuleringer. Dermed oppnås simulering av en full 3D-geometri av en UTTF fra inngangsspenning på senderen til utgangsspenning på mottakeren. Det er demonstrert at SimPAC2 kan brukes videre som et verktøy for design og optimalisering av UTTF, reduksjon av utviklingssyklusen og forbedring av nøyaktighet og linearitet.Ultrasonic Transit-Time Flowmeters (UTTF) and their modeling are on the main focus in this dissertation. UTTF can be categorized into clamp-on and inline devices depending on the needs of applications for flow measurement. Simulations, studies, and experimental verification of inline gas devices with high demands of accuracy are performed in the present work. It is demonstrated that with the use of simulations, it is conceivable to accelerate innovation, as well as to continuously improve measurement accuracy and technology for the fast-growing market of UTTF. In the present thesis, a multiphysics, hybrid numerical method is proposed i.e., a combination of a Finite Element Method (FEM) and a Finite Volume Method (FVM), for the purpose of 3D simulations and investigation of physical phenomena that affect the behavior of UTTF. The developed method, ’Simulations of Piezoelectricity, Acoustics, Coupled with CFD’ (SimPAC2), is used as a design tool of UTTF, as well as for the improvement of understanding the operation of UTTF. For the simulation, the UTTF is split into parts and the respective, more appropriate method is used for each part. More specifically, FEM is utilized for the simulation of piezoelectricity and structural acoustics in the solid parts i.e., the transducers and, if desired, partially the meter-body of the flowmeter. FEM is also used for the simulation of wave propagation in a part of the moving fluid medium. Acoustics and computational fluid dynamics (CFD) are considered in the moving fluid medium, as well as their interaction with each other with the use of FVM, which is traditionally more appropriate for CFD and large simulations that need to be highly parallelized. The hybrid SimPAC2 method requires complex interfaces between the FEM and FVM method, which are created in the course of the present work. A comparison of SimPAC2 results with pure CFD, FEM and measurements is carried out. A chain verification takes place, starting from a simulation of a simple geometry of piezoelectric elements in air in zero and uniform flow. Complexity is added with the simulation of a diametrical single-path flowmeter equipped with either piezoelectric elements or real transducers. Finally, a real industrial flowmeter with two chordal paths is simulated and measured in a flow rig, with the agreement of the results satisfying the set criteria. The simulations allowed for the systematic study and quantification of complex, much-anticipated effects in UTTF, such as 3D cavity effects, the position of flush, recessed, and protruded transducers, as well as the flow effect around the transducers and in the meter-body. The performed 3D multiphysics simulations capture interactions between ultrasonic waves and flow in the 3D geometry that are, by definition, not possible to be captured by 2D simulations. Before SimPAC2, the performance of systematic 3D multiphysics simulations was computationally expensive or impossible to perform. Thus, the simulation of a full 3D geometry of an UTTF is achieved from input voltage on the transmitter to output voltage on the receiver. It is demonstrated that SimPAC2 can be further used as a tool for the design and optimization of UTTF, the reduction of the development cycle and the improvement of accuracy and linearity.Doktorgradsavhandlin

Application of extended time-frequency domain average in ultrasonic detecting

Ultrasonic signal detection is essential for the ultrasonic-based applications such as ultrasonic flow measurements and nondestructive testing. The paper proposes three extended time-frequency domain average (ETFDA) techniques, which are based on the smoothed pseudo-Wigner-Ville distribution, continuous wavelet transform and Hilbert-Huang transform. These techniques combine beneficial time-frequency localization characteristics of the time-frequency analysis and abilities of the time domain averaging (TDA) to suppress noise interference. They are thus well adapted for detection of the ultrasonic signals even when they are strongly smeared by the noise or distorted in the medium. A number of tests conducted on simulated and actual ultrasonic signals have demonstrated that ETFDA provides a solid performance

Lattice Boltzmann Methods for Turbulent Flows – Application to Coriolis Mass Flowmeter

Komplexe Strömungsphänomene machen es schwierig Ingenieursanwendungen so detailliert und genau zu simulieren, dass eine Charakterisierung und Verbesserung ihres Funktionsprinzips möglich ist. Diese Arbeit zeigt, dass die Lattice-Boltzmann-Methode (LBM) sehr gut für diesen Zweck geeignet ist. Im Vordergrund stehen hierbei die Simulation und Modellierung von turbulenten Strömungen. Diese lassen sich auf Grund der hervorragenden Parallelisierbarkeit der LBM mit Large-eddy Simulationen an Stelle von Reynolds-gemittelten Navier--Stokes Modellen, die im industriellen Umfeld üblich sind, berechnen. Somit können komplexe transiente turbulente Strömungen simulativ untersucht werden. Die daraus gewonnenen Erkenntnisse dienen insbesondere der Auslegung und Optimierung von Bauteilen und Prozessen. Alle beschriebenen LBM Simulationen werden mit der Open Source Software OpenLB durchgeführt. Dazu wird OpenLB erweitert, um eine Validierung von implementierten Turbulenzmodellen mittels kanonischer Strömungsformen zu ermöglichen. Des Weiteren wird ein Framework für die Simulation von Fluid-Struktur Interaktion (FSI) geschaffen. Anfangs werden die Kollisionsoperatoren Bhatnagar--Gross--Krook (BGK), Entropic Lattice Boltzmann (ELB), Two-Relaxation-Time (TRT), Regularized Lattice Boltzmann (RLB) und Multiple-Relaxation-Time (MRT) in der Taylor-Green Vortex Strömung, einem klassischen Beispiel für abklingende homogene isotrope Turbulenz (DHIT), untersucht. Hierbei liegt der Fokus auf Stabilität, Konsistenz und Genauigkeit der verwendeten Schemata. Die Studie beinhaltet den Vergleich der turbulenten kinetischen Energie, der Dissipationsrate der Energie und dem Energiespektrum zu einer Referenzlösung. Drei unterschiedliche Reynoldszahlen, $\mathrm{Re}=800$, $\mathrm{Re}=1600$ und $\mathrm{Re}=3000$, werden sowohl unter Verwendung einer akustischen als auch einer diffusiven Skalierung betrachtet, um den Einfluss der Lattice Machzahl zu charakterisieren. In stark unteraufgelösten Gitterkonfigurationen zeigt das BGK Schema ein instabiles Verhalten. Divergierende Simulationen unter der Verwendung des MRT Schemas sind auf eine starke Abhängigkeit von der Lattice Machzahl zurückzuführen. Obwohl ELB die Viskosität verändert, kann kein Verhalten, das einem Wirbelviskositätsmodell entspricht, gefunden werden. Bei geringen Lattice Machzahlen zeigt das RLB Schema sehr geringe Energielevel bei hohen Wellenzahlen. Der ,,magic parameter" des TRT Schemas wird bestimmt im Hinblick auf den Energieeintrag. Trotzdem wird keine erhöhte Stabilität im Vergleich zum BGK Schema festgestellt. Insgesamt sollte die Lattice Machzahl bezüglich des verwendeten Kollisonsschemas gewählt werden, um die Stabilität zu gewährleisten und die Genauigkeit zu verbessern. Für die Realisierung eines wandmodellierten Large-Eddy Simulation (NWM-LES) Ansatzes wird der BGK Kollisionsoperator ausgewählt. Das Smagorinsky Wirbelviskositätsmodell kommt hierbei zum Einsatz und wird in der turbulenten Grenzschicht mit der van Driest\u27schen Dämpfungsfunktion verwendet. Der Einfluss verschiedener Implementierungen von Geschwindigkeitsrandbedingungen und Wandfunktionen wird in einer biperiodischen, voll ausgebildeten turbulenten Kanalströmung für Schubspannungs-Reynoldszahlen von $\mathrm{Re}_\tau=1000$, $\mathrm{Re}_\tau=2000$ und $\mathrm{Re}_\tau=5200$ untersucht. Die Validierung erfolgt mittels Daten einer direkten numerischen Simulation (DNS) für Turbulenzstatistiken erster und zweiter Ordnung. Die Anwendung dieses Ansatzes auf einen Coriolis Massendurchflussmesser (CMF) zeigt, dass der Druckverlust bis zu einer Reynoldszahl $\mathrm{Re}=127800$ beschrieben werden kann. Des Weiteren wird der entwickelte NWM-LES LBM Ansatz mit OpenFOAM, einer Open Source Implementierung der finititen Volumen Methode (FVM) für komplexe turbulente Strömungen, die relevant für Verbrennungsmotoren sind, verglichen. Der zuvor entwickelte und validierte LBM Ansatz wird mit einer Geschwindigkeitsrandbedingung für gekrümmte Ränder erweitert. Die Ergebnisse beider Strömungslöser werden mit Daten eines Particle Image Velocimetry (PIV) Experiments verglichen. Die Validierung umfasst sowohl die zeitgemittelten als auch die quadratisch gemittelten (RMS) Geschwindigkeitsfelder. Zusätzlich wird sowohl die Laufzeit der Simulation als auch die Dauer der unterschiedlichen Gittergenerierungsprozesse bestimmt. Die Performanceanalyse der getesteten Konfiguration zeigt, dass OpenLB 32-mal schneller ist als OpenFOAM. Folglich ist der entwickelte NWM-LES LBM Ansatz dazu in der Lage, komplexe turbulente Strömungen in einer Ingenieursanwendung akkurat und mit einem verringerten Rechenaufwand zu beschreiben. Wirbel induzierte Vibrationen (VIV) sind ein weiterer wichtiger Anwendungsfall für Ingenieursapplikationen. Für die Untersuchung dieser werden verschiedene Fluid-Struktur Ansätze für LBM implementiert, verglichen und evaluiert. Die zwei untersuchten Klassen sind die Moving Boundary Methods (MBM) und die Partially Saturated Methods (PSM). Als erstes wird die Galiläische Invarianz von aerodynamischen Koeffizienten für die einzelnen Schemata untersucht. Dazu wird das BGK Schema verwendet, um einen exzentrisch positionierten Zylinder in einer Couette Strömung zu simulieren. Überdies werden verschiedene Volumenapproximationsmethoden für PSM und Auffüllmechanismen für MBM verglichen. Sowohl die Gitterkonvergenz als auch die Konvergenz der Galiläischen Invarianz werden betrachtet. Die Studie der VIV-Phänomene umfasst einen transvers oszillierenden Zylinder in einem Freistrom bei einer Reynoldszahl von $\mathrm{Re}=100$. Dabei werden freie und erzwungene Oszillation betrachtet, um bekannte Phänomene, wie Lock-in und Lock-out Zonen, zu untersuchen. Die Ergebnisse zeigen, dass sowohl MBM als auch PSM eine gute Übereinstimmung zu Literaturdaten aufweisen, womit die Eignung für VIV-Simulationen bestätigt werden kann. Schließlich wird ein Fluid-Struktur Interaktionsansatz unter der Verwendung eines MBM Ansatzes für die Simulation eines CMFs realisiert. Hierbei wird OpenLB mit Elmer, einer Open Source Implementierung der Finite-Elemente-Methode, gekoppelt, um auch die Strukturdynamik zu beschreiben. Ein gestaffelter Kopplungsansatz zwischen den beiden Softwarepaketen wird präsentiert. Das Finite-Elemente-Gitter wird durch das Gittergenerierungstool Gmsh erstellt, um einen kompletten Open Source Workflow zu garantieren. Zunächst werden die Eigenmoden des CMFs berechnet und mit Messdaten verglichen. Die daraus bestimmte Anregungsfrequenz wird zur Bestimmung des Phasenshifts in einer partitionierten voll gekoppelten FSI Simulation verwendet. Der berechnete Phasenshift zeigt eine gute Übereinstimmung mit den Messdaten und bestätigt, dass dieses Modell in der Lage ist, das Funktionsprinzip eines CMFs zu beschreiben. Die durchgeführten Studien zeigen das große Potential der LBM für die Simulation von Ingenieursapplikationen, insbesondere wenn turbulente Strömungen betrachtet werden

Non-invasive classification of gas–liquid two-phase horizontal flow regimes using an ultrasonic Doppler sensor and a neural network

The identification of flow pattern is a key issue in multiphase flow which is encountered in the petrochemical industry. It is difficult to identify the gas–liquid flow regimes objectively with the gas–liquid two-phase flow. This paper presents the feasibility of a clamp-on instrument for an objective flow regime classification of two-phase flow using an ultrasonic Doppler sensor and an artificial neural network, which records and processes the ultrasonic signals reflected from the two-phase flow. Experimental data is obtained on a horizontal test rig with a total pipe length of 21 m and 5.08 cm internal diameter carrying air-water two-phase flow under slug, elongated bubble, stratified-wavy and, stratified flow regimes. Multilayer perceptron neural networks (MLPNNs) are used to develop the classification model. The classifier requires features as an input which is representative of the signals. Ultrasound signal features are extracted by applying both power spectral density (PSD) and discrete wavelet transform (DWT) methods to the flow signals. A classification scheme of '1-of-C coding method for classification' was adopted to classify features extracted into one of four flow regime categories. To improve the performance of the flow regime classifier network, a second level neural network was incorporated by using the output of a first level networks feature as an input feature. The addition of the two network models provided a combined neural network model which has achieved a higher accuracy than single neural network models. Classification accuracies are evaluated in the form of both the PSD and DWT features. The success rates of the two models are: (1) using PSD features, the classifier missed 3 datasets out of 24 test datasets of the classification and scored 87.5% accuracy; (2) with the DWT features, the network misclassified only one data point and it was able to classify the flow patterns up to 95.8% accuracy. This approach has demonstrated the success of a clamp-on ultrasound sensor for flow regime classification that would be possible in industry practice. It is considerably more promising than other techniques as it uses a non-invasive and non-radioactive sensor

Experimental investigations of two-phase flow measurement using ultrasonic sensors

This thesis presents the investigations conducted in the use of ultrasonic technology to measure two-phase flow in both horizontal and vertical pipe flows which is important for the petroleum industry. However, there are still key challenges to measure parameters of the multiphase flow accurately. Four methods of ultrasonic technologies were explored. The Hilbert-Huang transform (HHT) was first applied to the ultrasound signals of air-water flow on horizontal flow for measurement of the parameters of the two- phase slug flow. The use of the HHT technique is sensitive enough to detect the hydrodynamics of the slug flow. The results of the experiments are compared with correlations in the literature and are in good agreement. Next, experimental data of air-water two-phase flow under slug, elongated bubble, stratified-wavy and stratified flow regimes were used to develop an objective flow regime classification of two-phase flow using the ultrasonic Doppler sensor and artificial neural network (ANN). The classifications using the power spectral density (PSD) and discrete wavelet transform (DWT) features have accuracies of 87% and 95.6% respectively. This is considerably more promising as it uses non-invasive and non-radioactive sensors. Moreover, ultrasonic pulse wave transducers with centre frequencies of 1MHz and 7.5MHz were used to measure two-phase flow both in horizontal and vertical flow pipes. The liquid level measurement was compared with the conductivity probes technique and agreed qualitatively. However, in the vertical with a gas volume fraction (GVF) higher than 20%, the ultrasound signals were attenuated. Furthermore, gas-liquid and oil-water two-phase flow rates in a vertical upward flow were measured using a combination of an ultrasound Doppler sensor and gamma densitometer. The results showed that the flow gas and liquid flow rates measured are within ±10% for low void fraction tests, water-cut measurements are within ±10%, densities within ±5%, and void fractions within ±10%. These findings are good results for a relatively fast flowing multiphase flow

Vortex signal detection method with stochastic resonance based on adaptive coupled feedback control

The control of stochastic resonance is the key to its application. A feedback method is proposed to control the generation of stochastic resonance with coupling, and then enhance resonance effect with the optimization of control parameters. The method is applied to detect vortex signal. Artificial fish swarm algorithm is used to adjust the control variables adaptively, thus the optimal control of the coupled bistable stochastic resonance is realized. Numerical simulation and experimental results manifest that by this means the resonance effect can be enhanced effectively, the signal-to-noise ratio (SNR) of vortex signal can be improved, and the vortex shedding frequency can be obtained accurately

Experimental Investigation of Annular Flow Behaviour in Horizontal Pipe

The experimental investigations of annular flow were conducted in horizontal pipe using water/air in a 0.0504m internal diameter pipe loop with a total length of 28.68m. To understand annular flow behaviors, conductivity ring sensors, conductance probe sensors and Olympia high speed digital camera were used. In all the experiments, emphasis were on annular flow behavior, phase distribution and liquid film thickness. Liquid film thickness was observed to be thicker mostly when the superficial gas velocities were within 8.2699 m/s to 12.0675 m/s.  Above the aforementioned superficial gas velocities, the flow became uniformly distributed on the walls of the internal pipe diameter hence reducing the thicker liquid film at the bottom with gas core at the center of the pipe. More so, annular-slug flow was discovered in the investigation. At superficial liquid velocity of 0.0505 m/s-0.1355 m/s on superficial gas velocities of 8.2699 m/s – 12.0675 m/s, annular-slug flow was prominent. Also discovered was at superficial liquid velocities of 0.0903 m/s - 0.1355 m/s with respect to superficial gas velocities of 13.1692 m/s – 23.4575 m/s, the pipe walls are fully covered with liquid film at very high speed at the entire walls (upper walls and bottom). Also discovered in this experiment is the wavy flow of the upper walls. The liquid film thickness that flows at the upper pipe walls, creeps in a wavy flow. Therefore, the entire flow behavior in an annular flow could be grouped into; wavy-flow at the upper walls, annular-slug flow and thicker liquid film at the bottom with gas core at the center

A Study of Flowrate Calculation Using ESPRIT Technique for Ultrasonic Velocity Profiles

An ultrasonic Velocity Profile (UVP) has been continuously improved for flowrate measurements. Since the UVP can visualize a flow profile along a cross section of pipelines, it provides a significant advantage over other conventional methods such as differential pressure, turbine, and vortex. Previously, the UVP was realized by means of autocorrelation, fast Fourier transform, and wavelet as the signal-processing method. An Estimation of Signal Parameters via Rotational Invariance Technique (ESPRIT) has been widely used in a field of communication engineering for a high-resolution signal processing. This is the first of utilizing the ESPRIT technique in fluid mechanics for a flowrate computation. To guarantee the proposed idea, the results were compared with a standard electromagnetic flowmeter. Lab experiments were required to demonstrate the accuracy of flowrate measurements

A Scanning laser-velocimeter technique for measuring two-dimensional wake-vortex velocity distributions

A rapid scanning two dimensional laser velocimeter (LV) has been used to measure simultaneously the vortex vertical and axial velocity distributions in the Langley Vortex Research Facility. This system utilized a two dimensional Bragg cell for removing flow direction ambiguity by translating the optical frequency for each velocity component, which was separated by band-pass filters. A rotational scan mechanism provided an incremental rapid scan to compensate for the large displacement of the vortex with time. The data were processed with a digital counter and an on-line minicomputer. Vaporized kerosene (0.5 micron to 5 micron particle sizes) was used for flow visualization and LV scattering centers. The overall measured mean-velocity uncertainity is less than 2 percent. These measurements were obtained from ensemble averaging of individual realizations