Juan P L C Salazar | Universidade Federal de Santa Catarina - UFSC (Federal University of Santa Catarina) (original) (raw)

Papers by Juan P L C Salazar

Scopus, 2008

ABSTRACT Until recently, the phenomenon of inertial particle clustering in turbulence has been in... more ABSTRACT Until recently, the phenomenon of inertial particle clustering in turbulence has been investigated exclusively using direct numerical simulations (DNS). Numerous DNS studies have quantified the level of clustering in terms of the radial distribution function (RDF), which increases at small separations with increasing Stokes number, for small values of that parameter. The RDF is an important measure of clustering due to its connection with the enhancement in the inter-particle collision rate. A recent advancement in holographic imaging has enabled us to image a population of particles in a turbulent flow chamber in three dimensions to obtain a quantitative measure of the RDF experimentally. We will present comparisons of the experimental RDF with DNS. Additionally, with two rapidly pulsed images, we have measurements of the relative velocity statistics for particle pairs. We will present comparisons of the relative velocity statistics (mean inward velocity and probability density function) obtained from experiments with equivalent statistics taken from DNS as a function of separation distance. We show there is quantitative agreement between the two, with exception of the tails, where noise in the experiment has produced spuriously large relative velocities. We discuss the origins of those errors and some strategies for reducing them in the future.

The main objective of the present work is to establish a methodology capable of assessing, throug... more The main objective of the present work is to establish a methodology capable of assessing, through the use of a compact thermosyphon solar hot water heating system, the energy saving and electric energy peak reduction potential during the peak hours for a group of low-income residential consumers. In order to quantify these potentials, a total of 90 lowincome consumers were chosen to have their electric energy consumption monitored. Analysis of the collected data rendered relevant information for energy conservation policies, such as the hourly distribution of hot water consumption, the fraction of the electric energy consumption used for water heating, the average contribution of electric showerheads to the peak demand, and the estimated solar fraction for the group of consumers. The validation of the TRNSYS (Transient System Simulation Program) computational code for a thermosyphon solar water heating system is undertaken. The multi-objective economic optimization of constructive ...

Bulletin of the American Physical Society, 2005

DNS shows that aerosol particles, owing to their inertial mismatch with the lighter surrounding g... more DNS shows that aerosol particles, owing to their inertial mismatch with the lighter surrounding gas, will cluster in regions of high strain in turbulent flows. Particle radial distribution function (RDF) has been identified as a key variable used in the clustering theory. Due to the difficulties in D measurement of particulate flows and DNS at high Reynolds numbers, the dependence of RDF on the turbulence and particle parameters are not fully quantified. Our aim is to test the particle preferential concentration in an isotropic turbulent flow field using digital holographic PIV technique (DHPIV) and DNS at comparable conditions. The dependence of RDF on system parameters (e.g. particle size and response time) is explored using DNS. With the DHPIV, Particle 3D positions and velocities are measured directly via reconstructions from digital holographic recording. Good agreement between the experimentally obtained RDF and the simulations confirmed the existence of particle clustering, and quantified the dependence of RDF on the Stokes number. The results also confirm the capability to extend the exploration to a broader range of Reynolds number.

... 8:00 AM–10:36 AM, Sunday, November 19, 2006. Tampa Marriott Waterside Hotel and Marina Room: ... more ... 8:00 AM–10:36 AM, Sunday, November 19, 2006. Tampa Marriott Waterside Hotel and Marina Room: Florida Salon 123 Chair: James Riley, University of Washington Abstract ID: BAPS.2006.DFD ... Lujie Cao Jeremy de Jong Juan Salazar Lance Collins Scott Woodward Hui ...

Bulletin of the American Physical Society, Nov 1, 2006

in size, and the accuracy of most diagnostic techniques is sensitive to the particle size. To mak... more in size, and the accuracy of most diagnostic techniques is sensitive to the particle size. To make meaningful comparisons with experiments direct numerical simulations (DNS) must take into consideration the properties of the particles and model the limitations introduced by the diagnostics. We present a series of DNS of inertial particles in turbulence that were designed to match the measurements of Cao et al. In their experiments, the particle radial distribution function (RDF) was obtained from 3-D holographic images of particles in a turbulence box. DNS was done using the same particle size distribution as the particles in the experiments. The parameters of the flow (Re #) and the particles (St #) were matched. In the DNS, we eliminated particles below a specified size and recalculated the RDF to better match the experiments. Trends in the variation of the RDF with size cutoff were found to be non-intuitive, but can be explained based on an extension of the theory of Chun et al. (2005) to polydisperse particles. We optimized the cutoff size based on the comparison of the experimental and numerical RDF at one fan speed and applied the same cutoff to other fan speeds. The results showed good agreement. The comparison highlights the complexity of matching DNS and experimental observations.

Journal of Fluid Mechanics, Apr 9, 2008

We present digital holographic particle image velocimetry (DHPIV) measurements of the radial dist... more We present digital holographic particle image velocimetry (DHPIV) measurements of the radial distribution function (RDF) and the relative velocity probability density function (PDF) of inertial particle pairs in homogeneous isotropic turbulence generated by fans in an enclosed box. The RDF and relative velocity PDF are the essential statistical inputs to the particle-pair collision kernel (Sundaram & Collins 1997). The measurements

New Journal of Physics, 2012

Bulletin of the American …, 2006

Direct numerical simulations (DNS) of inertial clustering in turbulence are usually performed wit... more Direct numerical simulations (DNS) of inertial clustering in turbulence are usually performed with monodisperse particles having uniform-random initial spatial distribution. In these simulations, clustering statistics (e.g. radial distribution function) are obtained using full 3D spatial distribution. However, due to realistic constraints, most experiments to date are done with significant polydispersity, non-uniform particle initial spatial distribution and lower dimensional sampling. Here

A hybrid algorithm based on machine learning and quantum ensemble learning is proposed to find an... more A hybrid algorithm based on machine learning and quantum ensemble learning is proposed to find an approximate solution to a partial differential equation with good precision and favorable scaling in the required number of qubits. The classical part is composed by training several regressors (weaklearners), capable of solving a partial differential equation approximately using machine learning. The quantum part consists of adapting the QBoost algorithm to solve regression problems to build an ensemble of classical learners. We have successfully applied our framework to solve the 1D Burgers’ equation with viscosity, showing that the quantum ensemble method really improves the solutions produced by classical weak-learners. We also implemented the algorithm on the D-Wave Systems, confirming the best performance of the quantum solution compared to the simulated annealing and exact solver methods.

The main objective of the present work is to assess, through the use of a compact thermosyphon so... more The main objective of the present work is to assess, through the use of a compact thermosyphon solar hot water heating system with a backup electric showerhead heater, the energy conservation and the electric energy peak reduction potential during the peak hours for a group of low-income residential consumers in Florianópolis, Brazil (-27.6oS). In order to quantify these potentials, a total of 90 low-income consumers were chosen to have their electric energy consumption monitored. Analysis of the collected data rendered relevant information for energy conservation policies, such as the hourly distribution of hot water consumption, the fraction of the electric energy consumption used for water heating, the average contribution of electric showerheads to the peak demand, and the estimated solar fraction for the group of consumers.

An optimization method is proposed to size a compact solar domestic hot water system (CSDHWS) for... more An optimization method is proposed to size a compact solar domestic hot water system (CSDHWS) for low-income families with multiple hot water load profiles. The Life Cycle Savings (LCS) optimization is carried out using the Transient Simulation Program (TRNSYS) with the Generic Optimization Program (GenOpt) for Florianópolis (27.6S, 48.5W), Brazil. A total of seven variables are simultaneously optimized. Results can be used to locally optimize CSDHWS’s based on meteorological data. The proposed optimization method is an effective measure to reduce peak demand as well as total energy consumption.

O objetivo principal do trabalho foi o estabelecimento de uma metodologia de levantamento do pote... more O objetivo principal do trabalho foi o estabelecimento de uma metodologia de levantamento do potencial de economia e redução no pico da curva de demanda de energia elétrica no horário de ponta para consumidores de baixa renda, através do uso de sistemas de aquecimento solar compactos (com reservatório térmico integrado à placa coletora). Com o objetivo de quantificar esse potencial, um conjunto de 90 consumidores de baixa-renda, moradores de um condomínio residencial do Programa de Arrendamento Residencial da Caixa Econômica Federal, foi selecionado para ter o consumo de energia do chuveiro elétrico monitorado. A partir dos dados coletados, foi possível levantar informações relevantes para políticas de conservação de energia, como a distribuição horária do consumo de água quente, a contribuição do aquecimento de água para o consumo de energia elétrica residencial, a contribuição do chuveiro elétrico para o pico da curva de demanda, além da fração solar estimada do conjunto de residências. Paralelamente, realizou-se a validação de um modelo computacional de um sistema de aquecimento solar com reservatório térmico integrado para o software comercial TRNSYS (Transient System Simulation Program), com o objetivo de aumentar a credibilidade dos resultados apresentados obtidos mediante a extrapolação do consumo anual através de simulações. Uma revisão dos modelos de circuito termossifão é também apresentada. Com base em um perfil de consumo de água quente derivado a partir dos dados de medição in situ, faz-se uma otimização econômica de parâmetros construtivos através da programação multiobjetivo, levando em consideração o interesse do arrendatário e também o da concessionária de energia elétrica. Em um estudo de caso, a metodologia adotada fornece o valor da sobretaxa a ser cobrada pelo consumo de energia elétrica durante o horário de ponta em uma possível adoção de tarifa residencial diferenciada, além de dimensionar o sistema para um conjunto de consumidores com diferentes perfis de consumo de água quente. Os resultados apresentados neste trabalho são importantes para a determinação da viabilidade de políticas públicas para incorporação de sistemas de aquecimento solar às plantas de moradia para a população de baixa renda.

We present the first measurements of relative velocity statistics of inertial particles in a homo... more We present the first measurements of relative velocity statistics of inertial particles in a homogeneous isotropic turbulent flow with three-dimensional holographic particle image velocimetry (holographic PIV). From the measurements we are able to obtain the radial relative velocity probability density func- tion (PDF) conditioned on the interparticle separation distance, for distances on the order of the Kol- mogorov length scale. Together with measurements of the three-dimensional radial distribution function (RDF) in our turbulence chamber, these statistics, in principle, can be used to determine inter- particle collision rates via the formula derived by Sundaram and Collins (1997). In addition, we show temporal development of the RDF, which reveals the existence of an extended quasi-steady-state regime in our facility. Over this regime the measured two-particle statistics are compared to direct numerical simulations (DNS) with encouraging qualitative agreement. Statistics at the same Reynolds number but different Stokes numbers demonstrate the ability of the experiment to correctly capture the trends associated with particles of different inertia. Our results further indicate that even at moderate Stokes numbers turbulence may enhance collision rates significantly. Such experimental investigations may prove valuable in validating, guiding and refining numerical models of particle dynamics in turbulent flows.

Measuring the turbulent kinetic energy dissipation rate in an enclosed turbulence chamber that pr... more Measuring the turbulent kinetic energy dissipation rate in an enclosed turbulence chamber that produces zero-mean flow is an experimental challenge. Traditional single-point dissipation rate measurement techniques are not applicable to flows with zero-mean velocity. Particle image velocimetry (PIV) affords calculation of the spatial derivative as well as the use of multi-point statistics to determine the dissipation rate. However, there is no consensus in the literature as to the best method to obtain dissipation rates from PIV measurements in such flows. We apply PIV in an enclosed zero-mean turbulent flow chamber and investigate five methods for dissipation rate estimation. We examine the influence of the PIV interrogation cell size on the performance of different dissipation rate estimation methods and evaluate correction factors that account for errors related to measurement uncertainty, finite spatial resolution, and low Reynolds number effects. We find the Re λ corrected, second-order, longitudinal velocity structure function method to be the most robust method to estimate the dissipation rate in our zero-mean, gaseous flow system.

Physics of Fluids, Jan 1, 2012

In this study, we investigate the effect of “biased sampling,” i.e., the clustering of inertial p... more In this study, we investigate the effect of “biased sampling,” i.e., the clustering of inertial particles in regions of the flow with low vorticity, and “filtering,” i.e., the tendency of inertial particles to attenuate the fluid velocity fluctuations, on the proba- bility density function of inertial particle accelerations. In particular, we find that the concept of “biased filtering” introduced by Ayyalasomayajula et al. [“Modeling iner- tial particle acceleration statistics in isotropic turbulence,” Phys. Fluids 20, 0945104 (2008)], in which particles filter stronger acceleration events more than weaker ones, is relevant to the higher order moments of acceleration. Flow topology and its connec- tion to acceleration is explored through invariants of the velocity-gradient, strain-rate, and rotation-rate tensors. A semi-quantitative analysis is performed where we assess the contribution of specific flow topologies to acceleration moments. Our findings show that the contributions of regions of high vorticity and low strain decrease sig- nificantly with Stokes number, a non-dimensional measure of particle inertia. The contribution from regions of low vorticity and high strain exhibits a peak at a Stokes number of approximately 0.2. Following the methodology of Ooi et al. [“A study of the evolution and characteristics of the invariants of the velocity-gradient tensor in isotropic turbulence,” J. Fluid Mech. 381, 141 (1999)], we compute mean con- ditional trajectories in planes formed by pairs of tensor invariants in time. Among the interesting findings is the existence of a stable focus in the plane formed by the second invariants of the strain-rate and rotation-rate tensors. Contradicting the results of Ooi et al., we find a stable focus in the plane formed by the second and third invariants of the strain-rate tensor for fluid tracers. We confirm, at an even higher Reynolds number, the conjecture of Collins and Keswani [“Reynolds number scaling of particle clustering in turbulent aerosols,” New J. Phys. 6, 119 (2004)] that iner- tial particle clustering saturates at large Reynolds numbers. The result is supported by the theory presented in Chun et al. [“Clustering of aerosol particles in isotropic turbulence,” J. Fluid Mech. 536, 219 (2005)]. ⃝C 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4744993]

Journal of Fluid Mechanics, Jan 1, 2012

In the present study, we investigate the scaling of relative velocity structure functions, of ord... more In the present study, we investigate the scaling of relative velocity structure functions, of order two and higher, for inertial particles, both in the dissipation range and the inertial subrange using direct numerical simulations (DNS). Within the inertial subrange our findings show that contrary to the well-known attenuation in the tails of the one-point acceleration probability density function (p.d.f.) with increasing inertia (Bec et al., J. Fluid Mech., vol. 550, 2006, pp. 349–358), the opposite occurs with the velocity structure function at sufficiently large Stokes numbers. We observe reduced scaling exponents for the structure function when compared to those of the fluid, and correspondingly broader p.d.f.s, similar to what occurs with a passive scalar. DNS allows us to isolate the two effects of inertia, namely biased sampling of the velocity field, a result of preferential concentration, and filtering, i.e. the tendency for the inertial particle velocity to attenuate the velocity fluctuations in the fluid. By isolating these effects, we show that sampling is playing the dominant role for low-order moments of the structure function, whereas filtering accounts for most of the scaling behaviour observed with the higher-order structure functions in the inertial subrange. In the dissipation range, we see evidence of so-called ‘crossing trajectories’, the ‘sling effect’ or ‘caustics’, and find good agreement with the theory put forth by Wilkinson et al. (Phys. Rev. Lett., vol. 97, 2006, 048501) and Falkovich & Pumir (J. Atmos. Sci., vol. 64, 2007, 4497) for Stokes numbers greater than 0.5. We also look at the scaling exponents within the context of the model proposed by Bec et al. (J. Fluid Mech., vol. 646, 2010, pp. 527–536). Another interesting finding is that inertial particles at low Stokes numbers sample regions of higher kinetic energy than the fluid particle field, the converse occurring at high Stokes numbers. The trend at low Stokes numbers is predicted by the theory of Chun et al. (J. Fluid Mech., vol. 536, 2005, 219–251). This work is relevant to modelling the particle collision rate (Sundaram & Collins, J. Fluid Mech., vol. 335, 1997, pp. 75–109), and highlights the interesting array of phenomena induced by inertia.