High-fidelity simulation of an ultrasonic standing-wave thermoacoustic engine with bulk viscosity effects

We have carried out boundary-layer-resolved, unstructured fully-compressible Navier--Stokes simulations of an ultrasonic standing-wave thermoacoustic engine (TAE) model. The model is constructed as a quarter-wavelength engine, approximately 4 mm by 4 mm in size and operating at 25 kHz, and comprises a thermoacoustic stack and a coin-shaped cavity, a design inspired by Flitcroft and Symko (2013). Thermal and viscous boundary layers (order of 10 $\mathrm{\mu}$m) are resolved. Vibrational and rotational molecular relaxation are modeled with an effective bulk viscosity coefficient modifying the viscous stress tensor. The effective bulk viscosity coefficient is estimated from the difference between theoretical and semi-empirical attenuation curves. Contributions to the effective bulk viscosity coefficient can be identified as from vibrational and rotational molecular relaxation. The inclusion of the coefficient captures acoustic absorption from infrasonic ($\sim$10 Hz) to ultrasonic ($\sim$100 kHz) frequencies. The value of bulk viscosity depends on pressure, temperature, and frequency, as well as the relative humidity of the working fluid. Simulations of the TAE are carried out to the limit cycle, with growth rates and limit-cycle amplitudes varying non-monotonically with the magnitude of bulk viscosity, reaching a maximum for a relative humidity level of 5%. A corresponding linear model with minor losses was developed; the linear model overpredicts transient growth rate but gives an accurate estimate of limit cycle behavior. An improved understanding of thermoacoustic energy conversion in the ultrasonic regime based on a high-fidelity computational framework will help to further improve the power density advantages of small-scale thermoacoustic engines.Comment: 55th AIAA Aerospace Sciences Meeting, AIAA SciTech, 201

Modeling of Cross Correlation Flow Measurement Systems

In the work presented in this thesis, an original mathematical model of cross correlation flow measurement was developed, based on rigorous analysis of space-time development of a velocity field and vorticity field in turbulent flow. This model describes the effect of flow conditions on ultrasonic cross correlation flow meter output. Laboratory testing was conducted to validate the model. Results of numerical simulations based on the model were in good agreement with laboratory test results. Maximum deviation between results predicted by the model and experimental results was 3.2%, and average deviation was 1.1%. This model provides a basis for uncertainty analysis of cross correlation flow measurement, and its traceability to accepted industry standards, by describing the effect of various flow parameters and meter design parameters on flow measurement. Some of the results of this work are being used in industry today

Two-phase slug flow measurement using ultra-sonic techniques in combination with T-Y junctions

The accurate measurement of multiphase flows of oil/water/gas is a critical element of oil exploration and production. Thus, over the last three decades; the development and deployment of in-line multiphase flow metering systems has been a major focus worldwide. Accurate measurement of multiphase flow in the oil and gas industry is difficult because there is a wide range of flow regimes and multiphase meters do not generally perform well under the intermittent slug flow conditions which commonly occur in oil production. This thesis investigates the use of Doppler and cross-correlation ultrasonic measurements made in different high gas void fraction flow, partially separated liquid and gas flows, and homogeneous flow and raw slug flow, to assess the accuracy of measurement in these regimes. This approach has been tested on water/air flows in a 50mm diameter pipe facility. The system employs a partial gas/liquid separation and homogenisation using a T-Y junction configuration. A combination of ultrasonic measurement techniques was used to measure flow velocities and conductivity rings to measure the gas fraction. In the partially separated regime, ultrasonic cross-correlation and conductivity rings are used to measure the liquid flow-rate. In the homogeneous flow, a clamp-on ultrasonic Doppler meter is used to measure the homogeneous velocity and combined with conductivity ring measurements to provide measurement of the liquid and gas flow-rates. The slug flow regime measurements employ the raw Doppler shift data from the ultrasonic Doppler flowmeter, together with the slug flow closure equation and combined with gas fraction obtained by conductivity rings, to determine the liquid and gas flow-rates. Measurements were made with liquid velocities from 1.0m/s to 2.0m/s with gas void fractions up to 60%. Using these techniques the accuracies of the liquid flow-rate measurement in the partially separated, homogeneous and slug regimes were 10%, 10% and 15% respectively. The accuracy of the gas flow-rate in both the homogeneous and raw slug regimes was 10%. The method offers the possibility of further improvement in the accuracy by combining measurement from different regimes

Mathematical Modelling and Design for the Scale-up of an AACVD Process

The manufacturing process of photovoltaic devices, such as solar cells, relies on the production of Transparent and Conductive Oxide (TCO) films. One of the techniques for creating these films is based on Aerosol-Assisted Chemical Vapour Deposition (AACVD). The AACVD process comprises the atomisation of a precursor solution into aerosol droplets, which are transported to a heated chamber for the synthesis of films such as the TCOs, as well as coatings, powders, composites and nanotubes. At present, AACVD has not been used as an industrial deposition technique. However, it has the potential to be scaled-up due to its versatility and the ease through which effective functional coatings can be deposited at a laboratory-scale. Computational simulations are pivotal to study the feasibility of such a scale-up. This thesis presents, therefore, an integrated model to support the AACVD process scale-up. The model is comprised of four stages: aerosol generation, transport, delivery and chemical deposition. The generation of aerosol is described by a distribution of droplet sizes, which is the input to a transport model that incorporates the impact of aerosol losses. The output distribution provides sufficient information to predict the amount and sizing of aerosol reaching the deposition site. Experimental validation has shown the model to be effective at predicting transport losses and droplet sizes. The delivery stage includes the solvent evaporation, accounting for uncertainties in the temperature profile of the deposition site. This is a key factor for the solvent evaporation, setting the precursors free to react and form the desired products. For the chemical deposition stage, reactions in the solid and gas phases were studied. The model presented is suitable for application on the scale of industrial processes and is also suitable for processes that rely on atomisation and transport of particles, for example, spray drying or cooling and fuel combustion. Lessons learned in modelling uncertainties and their impact on process scale-up motivated the research into formulation, modelling and solution methods for such applications. Therefore, as an additional contribution, this thesis introduces Uncertainty.jl, a modelling framework focused on the treatment of uncertainty

Index to NASA Tech Briefs, 1975

This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs

Electrostatic Gas-Liquid Separation from High Speed Streams--Application to Advanced On-Line/On- Demand Separation Techniques

The separation of suspended droplets from gases has been one of the basic scientific and technical problems of the industrial era and this interest continues. Various industrial applications, such as refrigeration and HVAC systems, require control of fine droplets concentrations in moving gaseous mediums to maintain system functionality and efficiency. Separating of such fine droplets can be achieved using electrostatic charging as implemented in electrostatic precipitators (ESPs). They use electrostatic force to charge and collect solid particles. The objective of the present work was to study the feasibility of using wiretube electrostatic separator on the removal of fine water and oil droplets from air stream based on corona discharge ionization process. A parametric study was conducted to find key parameters affecting the separation process. This goal was approached by simulating the charging and separation phenomena numerically, and then verifying the modeling findings through experiments. The numerical methodology simulated the highly complex interaction between droplets suspended in the flow and electrical field. Two test rigs were constructed, one for air-water separation and the other for air-oil separation. A wiretube electrostatic separator was used as the test section for both test rigs. The separation performance was evaluated under different electric field and flow conditions. Finally, based on the results, a novel air-water separator prototype was designed, fabricated and tested. The numerical modeling results qualitatively showed acceptable agreement with the experimental data in terms of the trend of grade efficiency based on droplets size. Both numerical modeling results and experimental data showed that with a proper separator design, high separation efficiency is achievable for water and oil droplets. Based on the experimental data, at flow velocity of 5 m/s and applied voltage of 7.0 kV, the maximum separation efficiency for water and oil was 99.999 % and 96.267 %, respectively. The pressure drop was as low as 100 Pa and maximum power consumption was 12.0 W

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

In-line monitoring and control of rheological properties through data-driven ultrasound soft-sensors

The use of continuous processing is replacing batch modes because of their capabilities to address issues of agility, flexibility, cost, and robustness. Continuous processes can be operated at more extreme conditions, resulting in higher speed and efficiency. The issue when using a continuous process is to maintain the satisfaction of quality indices even in the presence of perturbations. For this reason, it is important to evaluate in-line key performance indicators. Rheology is a critical parameter when dealing with the production of complex fluids obtained by mixing and filling. In this work, a tomographic ultrasonic velocity meter is applied to obtain the rheological curve of a non-Newtonian fluid. Raw ultrasound signals are processed using a data-driven approach based on principal component analysis (PCA) and feedforward neural networks (FNN). The obtained sensor has been associated with a data-driven decision support system for conducting the process

Application of imaging techniques for characterizing MPI data

The Magnetic particle inspection (MPI) method is widely used in the industry for detecting surface or near surface flaws in ferromagnetic specimens. However, the attempts to quantify the physics underlying the method have been limited. This thesis is an effort to model the behavior of the magnetic particles under the influence of magnetic leakage fields. Imaging techniques are used to recreate the dynamics of the particles prior to their reaching an equilibrium around the flaw. The proposed approach has the capability to predict the time to equilibrium of the magnetic particles. Furthermore, the efficiency of the MPI method in terms of the fraction of the total number of particles around the flaw and the signal to noise ratio of the MPI image is predicted. The overall model can be used to obtain forward transfer functions between the flaw depth; and the time to equilibrium, efficiency and signal to noise ratio of the MPI image. Optimal experimental conditions for flaws of different depths are predicted