Robert Castilla

• PhD
• Professor (Assistant) at Polytechnic University of Catalonia

This work presents a study on the calculation of transmittance in an air handling unit (AHU) through three methods. A semi-empirical estimation based on simplified models of heat and mass transfer has been used. In addition, experimental tests were carried out in a real AHU under controlled conditions. The measured temperature inside and outside th...

This work presents a study on the calculation of transmittance in an Air Handling Unit (AHU) through three methods: theoretical estimation, experimental approach and numerical simulations. First, a theoretical estimation based on simplified models of heat and mass transfer in the AHU was employed. In addition, experimental tests were carried out in...

This paper presents and discusses the results of the “2024 International Computational Fluid Dynamics Challenge on the long-range indoor dispersion of pathogen-laden aerosols” aimed at assessing the ability of different computational codes and turbulence models to reproduce the dispersion of particles produced by a turbulent natural convection flow...

Supersonic vacuum generators, or ejectors, operate pneumatically to extract air from tanks in industrial applications. A key performance metric for ejectors is the Total Evacuation Time (TET), which measures the time required to reach minimum pressure. This research predicts TET using empirical models that rely on two key metrics: the characteristi...

Supersonic vacuum generators, or ejectors, operate pneumatically to extract air from a tank for industrial applications. A key performance metric for ejectors is the Total Evacuation Time (TET), which measures the time required to reach minimum pressure. This research predicts TET using analytical models that rely on two key metrics: the characteri...

This review paper provides an overview of recent advances in computational fluid dynamics (CFD) simulations of ejector pumps for vacuum generation. It examines various turbulence models, multiphase flow approaches, and numerical techniques employed to capture complex flow phenomena like shock waves, mixing, phase transitions, and heat/mass transfer...

This review paper provides an overview of recent advances in computational fluid dynamics (CFD) simulations of ejector pumps for vacuum generation. It examines various turbulence models, multiphase flow approaches, and numerical techniques employed to capture complex flow phenomena like shock waves, mixing, phase transitions, and heat/mass transfer...

There is currently increased interest in the use of alternatives to autoclaved culture media, in order to maintain the properties of the media, while saving energy and time. In this study, we assess a new system for culture media preparation, using a conventional microwave with a water bath and a glass bottle with a rubber cap that allows depressur...

In microbiology laboratories, it is essential to obtain high-quality samples where the culture media are completely homogeneous. The pour plate method includes having to melt the culture media—a mixture of agar and a nutrient solution—before seeding. A static mixer is designed for this purpose, employing CFD (Computational Fluid Dynamics) with the...

This paper presents and discusses the results of the "2022 International Computational Fluid Dynamics Challenge on violent expiratory events" aimed at assessing the ability of different computational codes and turbulence models to reproduce the flow generated by a rapid prototypical exhalation and the dispersion of the aerosol cloud it produces. Gi...

In recent years, Jupyter Notebooks have become a very useful free and open‐source tool in teaching, as they allow you to combine text, images, mathematical expressions, links and code into a single document. This gives students an interactive document with which they can experiment and learn with the help of high‐level mathematical calculus. In Flu...

In the era of rapid microbiological methods, there is a need to improve long-established culture techniques. Drawbacks of the pour plate method include having to melt each medium separately before seeding.

A vacuum supersonic ejector is an indispensable pneumatic device placed in nearly all industrial production lines. This device, also called a zero-secondary flow ejector, is characterized by the maximum entrained flow and the minimum secondary pressure. Numerical simulations were carried out by means of the CFD toolbox OpenFOAM v8 and its solver Hi...

Mechanical forces on the nucleus of a biological cell can play a significant role in its positioning within the cell. Some models for the migration of the nucleus are based on biochemical signals, which have a very slow response, and others on the mechanical actions of direct pushing-pulling forces, relying on the cytoskeleton and cell contractilit...

The aerodynamic complexity of the underbody surfaces of conventional road vehicles is a matter of fact. Currently available literature is focused mainly on very simple Ahmed-body geometries as opposed to realistic car shapes, due to their complexity and computational cost. We attempted to understand the flow behaviour around different realistic con...

The internal cushioning systems of hydraulic linear actuators avoid mechanical shocks at the end of their stroke. The design where the piston with perimeter grooves regulates the flow by standing in front of the outlet port has been investigated. First, a bond graph dynamic model has been developed, including the flow throughout the internal cushio...

The high complexity of current Formula One aerodynamics has raised the question of whether an urgent modification in the existing aerodynamic package is required. The present study is based on the evaluation and quantification of the aerodynamic performance on a 2017 spec. adapted Formula 1 car (the latest major aerodynamic update) by means of Comp...

Cells comprise mechanically active matter that governs their functionality, but intracellular mechanics are difficult to study directly and are poorly understood. However, injected nanodevices open up opportunities to analyse intracellular mechanobiology. Here, we identify a programme of forces and changes to the cytoplasmic mechanical properties r...

Supersonic ejectors are used in a wide range of applications such as compression of refrigerants in cooling systems, pumping of volatile fluids, or vacuum generation. The objective of the present paper is to mesh and simulate, in an OpenFOAM environment with an open access implicit density-based solver HiSA, the physics of the vacuum ejector, and,...

Supersonic ejectors are used extensively in all kind of applications: compression of refrigerants in cooling systems, pumping of volatile fluids or in vacuum generation. In vacuum generation, also known as zero-secondary flow, the ejector has a transient behaviour. In this paper, a numerical and experimental research of a supersonic compressible ai...

Over the years, numerous investigations have established the gerotor fundamentals. This work aims to provide a complete review of the literature from the last decade, focusing on the articles published in the past five years on gerotor technology in hydraulic machines. The report gives a catalogue of guidelines based on the trochoidal-envelope defi...

The fatigue of a hydraulic component inherently varies due to various factors that can be divided into two categories: structural and load spectrum variability. The effects of both variabilities must be considered when determining fatigue life. Compared with the structural variability, determining the variability in the load spectrums is more diffi...

Cushioning is an important aspect in hydraulic cylinder performance. The piston has to be decelerated before it strikes the end cap in order to avoid stresses in the cylinder components and reduce vibration that can be transmitted to the machine. One of the least-studied methods is internal cushioning by grooves in the piston. In this method, the f...

The trochoidal-gear technology has been growing in groundbreaking fields. Forthcoming applications are demanding to this technology a step forward in the conceiving stage of positive displacement machines. The compendium of the qualities and the inherent characteristics of trochoidal-gear technology, especially towards the gerotor pump, together wi...

A new approach for simulating liquid poured from a tilting lip spout is presented, using neither a dynamic mesh nor the moving solid solution method. In this case only the tilting ladle is moving, so we propose to rotate the gravitational acceleration at an angular velocity prescribed by a geometrical and dynamical calculation to keep the poured fl...

A new approach based on the open source tool OpenFOAM is presented for the numerical simulation of a mini gerotor pump working at low pressure. The work is principally focused on the estimation of leakage flow in the clearance disk between pump case and gears. Two main contributions are presented for the performance of the numerical simulation. On...

The technology of gerotor pumps is progressing towards cutting-edge applications in emerging sectors, which are more demanding for pump performance. Moreover, recent environmental standards are heading towards leakage-free and noiseless hydraulic systems. Hence, in order to respond to these demands, this study, which will be referred to as the Gero...

The trochoidal gear pump, also known as gerotor, owing to its remarkable advantages compared to other hydraulic pumps is chosen for many engineering applications. As each application is unique, the designer ought to be knowledgeable of the required specifications as a first task but need not be an expert in the hydraulic pump design. The review of...

The aim of this paper is to study the aerodynamics phenomena of a bass-reflex port that causes noise in the audible frequency range. After discarding structural and mechanical vibration issues, the hypothesis considered is that vortex shedding is the source of the noise. Experimental and numerical evidences of the vortex, an analysis of its noise a...

The aim of this paper is to study the aerodynamics phenomena of a bass-reflex port that causes noise in the audible frequency range. After discarding structural and mechanical vibration issues, the hypothesis considered is that vortex shedding is the source of the noise. Experimental and numerical evidences of the vortex, an analysis of its noise a...

All positive displacement pumps produce a pulsating flow. The present paper reports the experimental measurement of steady flow pulsations in the outlet of the internal wheeled pump. In the measured flow, the manufacturing tolerance are responsible of part of the spectra of the whole pulsation. Time-Resolved Particle Image Velocimetry technique has...

In the last few years, wall shear stress (WSS) has arisen as a new diagnostic indicator in patients with arterial disease. There is a substantial evidence that the WSS plays a significant role, together with hemodynamic indicators, in initiation and progression of the vascular diseases. Estimation of WSS values, therefore, may be of clinical signif...

The work presented in this article demonstrates the use of an empirical and simplified approach based on an optical technique and a home-made ad hoc code that give knowledge of the shape and falling velocity of a free-falling non-submerged liquid stream to predict its typology and flow rate. The visualization photographic technique is a non-intrusi...

A numerical study in a mini trochoidal-gear pump based on an ingenious strategy to adapt the background mesh to the profiles shape and a new boundary condition is presented. The strategy achieves a final background mesh better adapted to the geometries and, additionally, the cells are more homogenous and less distorted when the trochodial-profiles...

This article provides a technical description of a flexible hinge for wind tunnel rigs. For academic purposes, the device was integrated into several rod flexures to build a home-made external wind balance system. The cylindrical elastic element incorporates several notches, and the flexure linkage is able to transmit force in the main axial direct...

Trochoidal gear pumps produce significant flow pulsations that result in pressure pulsations, which interact with the system where they are connected, shortening the life of both the pump and circuit components. The complicated aspects of the operation of a gerotor pump make computational fluid dynamics the proper tool for modelling and simulating...

Recently several works have been published on numerical simulation of an external gear pump (EGP). Such kinds of pumps are simple and relatively inexpensive, and are frequently used in fluid power applications, such as fluid power in aeronautical, mechanical, and civil engineering. Nevertheless, considerable effort is being undertaken to improve ef...

“Mechanics” and “Fluids” are familiar concepts for any newly-registered engineering student. However, when combined into the term “Fluid Mechanics”, students are thrust into the great unknown. The present article demonstrates the process of adaptation employed by the Fluid Mechanics course in the undergraduate engineering program, along with the te...

The numerical analysis of an external gear pump with cavitation effects has been validated with experimental data obtained by applying Time-Resolved Particle Image Velocimetry. The effect of inlet and outlet pressure on volumetric efficiency has been studied numerically. First, the Particle Image Velocimetry method was used to analyze the two-dimen...

There are multiple processes at different scales that produce turbulent mixing in the ocean, thus giving a large variation of horizontal eddy diffusivities, we use a direct method (Einstein's diffusion equation) to evaluate the influence of ambient parameters, such as wave height, wind or local currents on coastal dispersion. At the same time numer...

Polydimethylsiloxane (PDMS) is one of the most common materials used for the flow delivery in the microfluidics chips, since it is clear, inert, non-toxic and non-flammable. Its inexpensiveness, straightforward fabrication and biological compatibility have made it a favorite material in the exploratory stages of the bio-microfluidic devices. If sma...

This article provides a technical description of a flexible hinge for wind tunnel rigs. For academic purposes, the device was integrated into several rod flexures to build a home-made external wind balance system. The cylindrical elastic element incorporates several notches, and the flexure linkage is able to transmit force in the main axial direct...

Prediction and reduction of pressure drop and resistance flow in micropillar arrays is important for the design of microfluidic circuits used in different lab-on-a-chip and biomedical applications. In this work, a diamond microchannel integrated micropillar pump (dMIMP) with a resistance flow 35.5% lower than circular based micropillar pump (cMIMP)...

Recent technology advancements in Particle Image Velocimetry (PIV) technique offers a new possibility to study the complex turbulent flows over a wide range of scales. It can be used for the estimation of the turbulent kinetic energy dissipation rate including spatial derivatives of the velocity fluctuation components. In this study the flow charac...

Hydraulic machines are faced with increasingly severe performance requirements. The need to design smaller and more powerful machines rotating at higher speeds in order to provide increasing efficiencies has to face a major limitation: cavitation. The problem is inherently three-dimensional, due to the axial clearances, the relief and circumferenti...

A gerotor pump, which is widely used in the automotive industry for engine oil lubrication, produces an instantaneous flow fluctuation and the estimation of this is fundamental in order to evaluate the pump quality for silent and smooth operation. The intricate aspects of the pumping process of a gerotor pump make computational fluid dynamics the a...

Time-Resolved Particle Image Velocimetry (TRPIV) has been used to investigate the flow inside the suction chamber of an external gear pump where the movement of the fluid through the pump is maintained by the rotation of the gears. The main purpose of this paper is to study the characteristics of the complex flow pattern of this pump system in orde...

The flow in the suction chamber of an external gearpump is numerically analysed. The evolution of the boundaries of the domain is very complex, and an arbitrary Lagrangian–Eulerian (ALE) formulation is used with mesh deformation and local remeshing. Nevertheless, a mesh replacement strategy is also adopted in order to avoid skewed meshes and allow...

In order to measure eddy diffusivity in the ocean using a scaling that includes the thickness of the surf zone as well as the depth and the wave period[1,2]. Measurements in the Mediterranean are almost two orders of magnitude smaller than in the Pacific coast. On a larger scale, and further away from the coast the relevant eddy diffusivities are m...

Experimental results of turbulent flows in the sea surface near the coastline have been performed using both Lagrangian and Eulerian methods, field tests are presented using video recordings and velocity sensors[1]. The spatial and temporal resolution is limited by the measuring instruments, which results in "filtering" out the very small scales. T...

Data from SABLES98 experimental campaign have been used in order to study the influence of stability (from weak to strong stratification) on intermittency [1]. Standard instrumentation, 14 thermocouples and 3 sonic anemometers at three levels (5.8, 13.5 and 32 m) were available in September 1998 and calculations are done in order to evaluate struct...

This paper describes a numerical analysis of the dynamics of the shaft in the journal bearing of a gear pump. The modulus and direction of the load is a function of the relative position of the gears, causing a precession motion around an equilibrium position. The mean load is the function of the working pressure of the gear pump. The numerical ana...

In recent years the industrial applications of porous materials has shown a growing relevance. Most of the technological thermal processes in porous media involve time-dependent thermal conditions. Therefore, the temperature at each point of the material also changes in time. In order to correctly carry out the technological process, it becomes nec...

The movement of the shaft of a driven gear in a gear pump is experimentally studied. Three different methods are considered, and the use of a laser micrometer measurement method is validated. In order to use the laser micrometer, some modifications are made to the gear pump. Experimental results for different working pressures and rotational veloci...

Experimental results of turbulent flows in the sea surface near the coastline have been performed using both Lagrangian and Eulerian methods, field tests are presented using video recordings and velocity sensors. The spatial and temporal resolution is limited by the measuring instruments, which results in "filtering" out the very small scales. The...

An innovative tool for the improvement of the design methodology of a trochoidal gear, which works as a part of a hydraulic pump, is introduced. For the past few years, new, specific, and demanding applications of this type of pumps have demanded to maximize efficiency and to reduce manufacturing costs by improving its two main performance indexes:...

Implementation of Active Transparent Façades (ATF) in buildings has been an object of broad application in recent years, both in new or existing buildings. However, there is little experience in the predicting the operating behavior of an ATF. Sometimes the results obtained are not satisfactory and an extra energetic cost is necessary to obtain sui...

Richtmyer-Meshkov instability occurs when a shock wave impinges on an interface separating two fluids having different densities [1,2]. The instability causes perturbations on the interface to grow, bubbles and spikes, producing vortical structures which potentially result in a turbulent mixing layer. In addition to shock tube experiments, the inco...

The diffusion of a tracer in a two dimensional turbulent flow which is forced by non-homogeneous distribution is dominated by the structures in the flow. In case of acceleration producing baroclinic vorticity due to density differences, Instabilities such as the Rayleigh-Taylor [1] or the Kelvin-Helmholtz appear. These are investigated using multi-...

The use of air bubbles for the analysis of the turbulence in the suction chamber of a gear pump with Time Resolved Particle Image Velocimetry (TRPIV) is considered. It is the first time, as far as the authors know, that the flow inside a gear pump is observed with a non-intrusive technique. Although there are drawbacks of using air bubbles as flow...

El flujo turbulento se expresa como la suma de una velocidad media u y la fluctuación de velocidad u. La velocidad media es la responsable del transporte de la mancha en conjunto, y es, básicamente , la velocidad debida a las corrienes de superficie. Las fluctuaciones de velocidad están producidas por un aporte externo de energia, debido al viento,...

Time Resolved Particle Image Velocimetry (TRPIV) has been used to investigate the turbulent flow in an external gear pump. The fluid movement through the pump is maintained by the rotation of the gears that carries the fluid from the intake side to the discharge side of the system. Small air bubbles have been used as flow seeding to obtain the imag...

We study numerically the comparison between Lagrangian experiments on turbulent particle dispersion in 2-D turbulent flows performed, on the one hand, on the basis of direct numerical simulations (DNS) and, on the other hand, using kinematic simulations (KS). Eulerian space-time structure of both DNS and KS dynamics are not comparable, mostly due t...

We study numerically the comparison between Lagrangian experiments on turbulent particle dispersion in 2-D turbulent flows performed, on the one hand, on the basis of direct numerical simulations (DNS) and, on the other hand, using kinematic simulations (KS). Eulerian space-time structure of both DNS and KS dynamics are not comparable, mostly due t...

The aim of the approach of this paper is to characterise contact stress of a trochoidal-gear set when it works as part of the hydraulic machine. It is important to know that the contact stress forces in a trochoidal-type machine is important because the machine cannot be adjusted for wear. The main difficulty in calculating the contact forces is to...

The effect of stratification on turbulence, among other effects produces significant changes in the power spectrum. For homogeneous turbulence at large Reynolds numbers a spectral subrange of - 5/3 (Kolmogorov 1942) may be found, while for two dimensional turbulence the spectrum follows a -3 law (Kraichnan 1970). Here we compare Lagrangian and Eule...

The dependence of the proporcionality constant of the quadratic time growth law of the non-linear mixing zone in Rayleigh-Taylor experiments on several parameters is considered in this work. If different initial perturbations are taken into account and the effect of the large scale initial perturbation is substracted from the growth of the mixing i...