Enrique Sanmiguel Rojas

• Ph.D.
• Professor (Full) at University of Malaga (Spain)

Experimental measurements in a wind tunnel of the unsteady force and moment that a fluid exerts on flexible flapping aerofoils are not trivial because the forces and moments caused by the aerofoil's inertia and others structural tensions at the pivot axis have to be obtained separately and subtracted from the direct measurements with a force/torque...

A new theoretical model is presented for an aquatic vehicle self-propelled by a rigid foil undergoing pitching oscillations generated by a torque of small amplitude applied at an arbitrary pivot axis at which the foil is elastically supported to allow for passive heaving motion. The model is based on 2D linear potential-flow theory coupled with the...

We explore numerically and theoretically the capability of flexible foils elastically mounted to translational springs and dampers at the leading edge to extract energy from low-speed winds through its passive heave motion. Given the spring and foil stiffnesses, for each damper constant the theory (which is valid for high Reynolds numbers and small...

High-resolution numerical simulations of the self propelled locomotion of two-dimensional pitching foils are used to assess simplified models based on linear potential theory for the fluid-foil interaction. These models are very useful because they provide simple analytical estimations of the swimming velocity, among other relevant features of the...

Purpose This paper aims to analyze the propulsive performance of small-amplitude pitching foils at very high frequencies with double objectives: to find out scaling laws for the time-averaged thrust and propulsive efficiency at very high frequencies; and to characterize the Strouhal number above which the effect of turbulence on the mean values can...

The fluid-structure interaction of a flexible plunging hydrofoil immersed in a current is solved numerically to analyze its propulsion enhancement due to flexibility at Reynolds number 10 000. After validating with available experimental data, the code is used to assess analytical predictions from a linear theory. We consider large stiffness ratios...

The present work is focused on the numerical study of a solar-powered Stirling engine, with the particularity that the solar radiation is injected through a transparent top cover. Thus, the working fluid absorbs the heat across a porous layer of a steel woven wire screen placed alongside the inner side of the transparent wall. The engine output net...

Numerical simulations of the flow around a NACA0012 pitching foil are presented to investigate the effect of the pivot axis location on its propulsive performance for a Reynolds number Re=16000. The pivot point position a is varied between the foil’s leading edge (a=−1) and its trailing edge (a=1). A wide range of values of the reduced frequency k...

The variation of the lift coefficient in a symmetric airfoil (NACA 0012 profile) at very small angles of attack is studied experimentally and numerically for a range of low chord-based Reynolds numbers, Re. Experimentally, the non-linearity around the zero angle of attack leading to a switch in sign on the lift was observed for a big enough aspect...

To elucidate the role played by surface tension on the formation and on the structure of a circular hydraulic jump, the results from three different approaches are compared: the shallow-water (SW) equations without considering surface tension effects, the depth-averaged model (DAM) of the SW equations for a flow with a parabolic velocity profile, a...

Several semiempirical models for the thrust force and propulsion efficiency of pitching foils have been developed recently to derive simple scaling laws for aquatic locomotion. In this work, we compare two of these models with the theoretical results from linear potential theory and with available experimental data. Overall, the results from the co...

High cavitating or supercavitating flows in fuel injector systems are crucial since they improve the mixing and the fuel atomization into combustion chambers, decreasing both fuel consumption and pollutant emissions. However, there is a lack of information regarding the required time to obtain high cavitating flows at the nozzle outlet, from the st...

Anthropological research on the functionality of the upper airways has focused on the study of the nasal cavity at skeletal cranial level. However, the soft tissue that makes up this entire structure has received less attention from researchers. The aim of this study is to analyze the morphology of the soft tissues of different functional component...

Introduction: Nasoseptal perforations (NSP) are becoming common in the modern world, and can cause a wide variety of symptoms, including a sensation of nasal obstruction, epistaxis, crusting, dryness, headache, nasal pain and a whistling sound. There is an extensive range of surgical treatment techniques, but reported results were rarely statistic...

Annually, hundreds of thousands of surgical interventions to correct nasal airway obstruction are performed throughout the world. Recent studies have noted that a significant number of patients have persistent symptoms of nasal obstruction postoperatively. In the present work, we introduce a new methodology that raises the success rate of nasal cav...

Introduction Computational fluid dynamics (CFD) is a mathematical tool to analyse airflow. We present a novel CFD software package to improve results following nasal surgery for obstruction. Methods A group of engineers in collaboration with otolaryngologists have developed a very intuitive CFD software package called MeComLand®, which uses the pa...

Background and purpose: Recent studies have demonstrated that a significant number of surgical procedures for nasal airway obstruction (NAO) have a high rate of surgical failure. In part, this problem is due to the lack of reliable objective clinical parameters to aid surgeons during preoperative planning. Modeling tools that allow virtual surgery...

The upper airways are key for the respiratory function and thus essential for understanding the biology of the human organism (Elad et al. 2008). Although the functionally relevant structures of the airways consist mostly of soft tissue, most studies in physical anthropology and Paleobiology have focused on the morphology of the skeletal features o...

Introduction: Computational fluid dynamics (CFD) is a mathematical tool to analyse airflow. We present a novel CFD software package to improve results following nasal surgery for obstruction. Methods: A group of engineers in collaboration with otolaryngologists have developed a very intuitive CFD software package called MeComLand®, which uses th...

Computational fluid dynamics (CFD) is a mathematical tool to analyse airflow. As currently CFD is not a usual tool for rhinologists, a group of engineers in collaboration with experts in Rhinology have developed a very intuitive CFD software. The program MECOMLAND(®) only required snapshots from the patient's cross-sectional (tomographic) images, b...

There are significant variations of both human nose shapes and airflow patterns inside nasal cavities, so it is difficult to provide a comprehensive medical identification using a universal template for what otolaryngologists consider normal breathing at rest. In addition, airflow patterns present even more random characteristics in diseased nasal...

It is known that the exhaust stream of internal combustion engines contains soot agglomerates with fractal geometries. The samples of real soot agglomerates can only be analyzed from projections observed with powerful microscopes. The fractal dimension of an agglomerate is estimated from the combination of its volume and a characteristic radius. Th...

The sliding velocity plays an important role on the energetic efficiency and longer life of cam mechanisms with flat-faced translating followers. In this work, an optimization procedure published recently and based in the Bézier curves, is adapted to minimize the sliding velocities in this kind of cam mechanisms. Specifically, when the maximum lift...

We develop analytical approaches and analyze their range of applicability to oscillators with two nonlinear springs in parallel and series connections. Specifically, we focus our study on systems with hardening springs and cubic nonlinearities. In both cases, three dimensionless parameters govern the oscillator namely λ = k2/k1 and ε1,2 = ε1,2A^...

The thrust efficiency of a two-dimensional heaving airfoil is studied computationally for a low Reynolds number using a vortex force decomposition. The auxiliary potentials that separate the total vortex force into lift and drag (or thrust) are obtained analytically by using an elliptic airfoil. With these auxiliary potentials, the added-mass compo...

The two-dimensional flow around a rotating cylinder is investigated numerically using a vorticity forces formulation with the aim of analyzing quantitatively the flow structures, and their evolutions, that contribute to the lift and drag forces on the cylinder. The Reynolds number considered, based on the cylinder diameter and steady free stream sp...

The Gardner–Ostrovsky equation, also known as the extended rotation-modified Korteweg–de Vries (KdV) equation, describes weakly nonlinear internal oceanic waves under the influence of Earth’ rotation. High accuracy numerical methods are needed to follow with precision the long time evolution of the solutions of this equation, with the additional di...

We present a three-dimensional numerical study on the drag reduction of a D-shaped body, of chord length L , height H and spanwise width W , with H/W⪯¡1H/W⪯¡1, aligned with a turbulent incompressible free-stream of velocity U∞U∞, density ρ and viscosity μ . In particular, an extensive parametric study is performed numerically using the IDDES turbul...

We analyze the global linear stability of the axisymmetric flow around a spinning bullet-shaped body of length-to-diameter ratio L/D=2, as a function of the Reynolds number, Re=ρw∞D/μ, and of the rotation parameter Ω=ωD/(2w∞), in the ranges Re<450 and 0≤Ω≤1. Here, w∞ and ω are the free-stream and the body rotation velocities respectively, and ρ and...

We analyse the effects of the air ambient temperature on the airflow across a Caucasian nasal cavity under different ambient temperatures using CFD simulations. A three-dimensional nasal model was constructed from high-resolution computed tomography images for a nasal cavity from a Caucasian male adult. An exhaustive parametric study was performed...

Tanto el estilo como el contenido de este texto son el resultado de mu-chos años de docencia universitaria e investigación. Este libro se ha escrito pensando en los alumnos que cursan estudios, tanto de grado como de máster, relacionados con la Ingeniería Mecánica. En el texto se desarrollan métodos analíticos y numéricos para la resolución de los...

We present a numerical study on the drag reduction of a two-dimensional bluff body with a blunt trailing edge, which has a chord length L, body height H and spanwise width W, being H/W≪1, aligned with a turbulent incompressible free-stream of velocity U∞, density ρ and viscosity μ. In particular, an extensive parametric study is performed numerical...

Experimental results for instabilities present in a rotating Hagen–Poiseuille flow are reported in this study through fluid flow visualization. First, we found a very good agreement between the experimental and the theoretical predictions for the onset of convective hydrodynamic instabilities. Our analysis in a space–time domain is able to obtain q...

Results of three-dimensional numerical simulations of the flow through a sudden expansion in a pipe are presented. The axisymmetric state is known to be stable over the range of Reynolds numbers studied, but recent experimental results suggest bifurcation phenomena. A resolution of this dichotomy between calculation and experiment is provided using...

The proliferation of atria within modern large buildings is relatively recent. An atrium can be defined as a large open space connecting two or more storeys. Atria are important architectonical features since the 60’s and can be found, among others, in shopping centres, office buildings and high-rise buildings, airports, stations and sports centres...

We extend our previous research on the instability properties of the laminar incompressible flow of density &rgr; and viscosity μ, which develops behind a cylindrical body with a rounded nose and length-to-diameter ratio L/D = 2, aligned with a free-stream of velocity w∞ [E. Sanmiguel-Rojas &etal;, Phys. Fluids 21, 114102 (2009); P. Bohorquez &etal...

We study by means of experiments and numerical simulations the periodic breakup of an air sheet surrounded by a co-flowing water sheet, for a fixed liquid- to-gas thickness ratio, h = hw,0^*/ha,0^*˜5.27, as a function of their control parameters, namely the Weber number, We=ρw,w,0^*2 ,a,0^*/σ, and the water-to-air velocity ratio, λ=uw,0^*/ua,0^*, w...

Numerical simulations are performed for laminar flow past a rotating bullet-shaped body of length-to-diameter ratio L/D=2, ranging the non-dimensional angular rotation velocity, φ=φR/u∞, from 0 to 0.6, and covering the Reynolds number range 320<Re<430. Three transition patterns stand out as φ increases on the parametric map φ- Re. When φ<=0.3, incr...

We study the transition between the two regimes experimentally observed when a plane air sheet surrounded by a coflowing water sheet discharges into stagnant air: a bubbling regime, which leads to the periodic break-up of the air sheet, and a jetting regime, where both sheets evolve slowly downstream without breaking. A jetting-to-bubbling transiti...

The dynamics of a plane air sheet surrounded by a coflowing water film, discharging into stagnant air, is investigated by means of experiments and linear stability theory. For fixed values of the water-to-air thickness ratio, h = hw,0*/ha,0* ≃ 5.27, and of the air-to-water density ratio, S = ρa/ρw ≃ 0.0012, two different flow regimes are experiment...

Front Cover (OFC, IFC) and matter

We investigate the stability properties and flow regimes of laminar wakes behind slender cylindrical bodies, of diameter D and length L, with a blunt trailing edge at zero angle of attack, combining experiments, direct numerical simulations and local/global linear stability analyses. It has been found that the flow field is steady and axisymmetric...

We investigate the stability properties and flow regimes of laminar wakes behind slender cylindrical bodies, of diameter D and length L, with a blunt trailing edge at zero angle of attack, combining experiments, direct numerical simulations and local/global linear stability analyses. It has been found that the flow field is steady and axisymmetric...

A new coefficient to characterize the global behaviour of adiabatic compressible flow at T-junctions is proposed. The new coefficient is defined according to the conclusions derived from the uncertainty propagation analysis of the total pressure loss coefficient defined by Miller for compressible flow. The numerical results obtained using the new l...

The dynamics of a plane air sheet surrounded by a co-flowing water sheet, discharging into stagnant air, has been investigated by means of experiments and numerical simulations with the aim at proposing new geometrical configurations for air bubble generation. In this case, the problem is governed by the Weber number, We = rhow,w^2,a/sigma, and the...

We extend our previous research on the instability properties of the laminar incompressible flow around a cylindrical body with a rounded nose and length-to-diameter ratio L/D=2, at zero angle of attack, by analyzing the effects of a cylindrical base cavity of length h and diameter Dc. We combine experiments, three-dimensional direct numerical simu...

This paper provides with a set of full-scale experimental data of atrium fires. These data could be used as benchmarks for future numerical validation studies. In particular, the influence of the make-up air velocity as well as the position and area of the vents in an atrium is assessed both experimentally and numerically. Experimentally, the effec...

This paper aims to study the influence of different make-up air configurations on the inner conditions induced by low-power fires within an atrium. For this objective, three full scale fire tests in a 19.5 m x 19.5 m x 19.5 m facility have been conducted. In these tests, symmetric and non-symmetric make-up air configurations, as well as different a...

We report the results of the global mode analysis to characterize the onset of unsteadiness in a circular pipe flow through an axisymmetric sudden expansion of inlet-to-outlet diameter ratio of d/D=0.5. We find that the axisymmetric state becomes linearly unstable at a significantly higher critical Reynolds number than the one reported in previous...

The flow around a slender body with a blunt trailing edge is unstable in most situations of interest. Usually the flow instabilities are generated within the wake behind the bluff body, inducing fluctuating forces and introducing the possibility of resonance mechanisms with modes of the structure. Base bleed is a simple and well-known means of stab...

We investigate the instability properties of the laminar incompressible flow around a cylindrical body with a rounded nose and length-to-diameter ratio 2, at zero angle of attack, combining experiments, three-dimensional direct numerical simulations and a global linear stability analysis. The direct numerical simulations and the global stability re...

Atria and large spaces are common architectonical features in modern buildings such as high rises, auditoria, warehouses, airports and mass transport stations among others. There is currently an international trend towards the performance-based design for fire safety of these building elements. This design process relies heavily on fire modelling b...

New experimental correlations to characterize energy losses in adiabatic compressible flow at 90-degree T-junctions and their expanded uncertainties are presented. These new correlations are based on a new linking between branches coefficient definition, Kˆ, and show a logarithmic relationship with mass flow rate ratio between branches, q, and the...

The use of computational fluid dynamics (CFD) as a tool for buildings, warehouses or factories design requirements fulfilling about fire safety is becoming more common and reliable. Performance-based fire safety assurance procedures make use of the CFD fire modelling to anticipate the evolution of fire, but they need always to be validated. This is...

Numerical simulations of steady incompressible laminar 3D fluid flow with heat transfer in smooth round tubes with wire coil inserts have been accomplished. Four wire coils with different geometrical characteristics of dimensionless pitch (p/d) and wire-diameter (e/d) have been studied for Reynolds numbers lower than 500–700 using the commercial pa...

We have performed a series of three-dimensional (3D) numerical simulations of the incompressible flow discharging from a rotating pipe into a coaxial static cylindrical container through a sudden expansion. We have considered several values of the Reynolds number based on the pipe flow rate ReQ between 50 and 300, and an expansion diameter ratio of...

Base bleed is a simple and well-known means of stabilizing the wake behind slender bodies with a blunt trailing edge. In the present research, we investigate the global instability properties of the laminar-incompressible flow using a spectral domain decomposition method to perform the global stability analysis. In particular, we describe the flow...

The baroclinic stability of a family of two time-level, semi-implicit schemes for the 3D hydrostatic, Boussinesq Navier–Stokes equations (i.e. the shallow water equations), which originate from the TRIM model of Casulli and Cheng (Int. J. Numer. Methods Fluids 1992; 15:629–648), is examined in a simple 2D horizontal–vertical domain. It is demonstra...

A global methodology has been developed and validated to obtain the total pressure loss coefficient in internal compressible flow in T-type junctions. This methodology is based on the calculation of the thermo-fluid properties extrapolated to the branch axes intersection, once the straight pipe friction losses numerically calculated have been subtr...

We report results from three-dimensional numerical simulations of the incompressible flow in a vertical pipe of circular cross-section discharging from a cylindrical container. Natural Coriolis forces due to the Earth rotation triggers the instability of the axisymmetric flow, and nonlinear spiral waves with azimuthal wave number |n|=3 are formed a...

A global methodology has been developed and validated to obtain the total pressure loss coefficient in internal compressible flow at T-type junctions. This methodology is based on the calculation of the thermo-fluid properties extrapolated to the branch axes intersection, once the straight pipe friction losses numerically calculated have been subtr...

The three-dimensional (3D) structure of a jet of water coming out of a rotating circular pipe into a quiescent tank of water is analyzed both experimentally (through LDA and PIV techniques), and numerically, for several values of the Reynolds number (Re) of the order of a few hundreds, and for several values of the swirl parameter (L). The observed...

A method for generating a non-uniform Cartesian grid for irregular two-dimensional (2D) geometries such that all the boundary points are regular mesh points is given. The resulting non-uniform grid is used to discretize the Navier–Stokes equations for 2D incompressible viscous flows using finite-difference approximations. To that end, finite-differ...

To investigate the nature of nonlinear waves appearing in an axially rotating pipe, we have performed a series of time-depending, three-dimensional numerical simulations of the incompressible Navier-Stokes equations in a rotating long pipe. As a difference with some previous works on the subject, which look for several given types of traveling wave...

A finite-difference method for solving the incompressible time-dependent three-dimensional Navier–Stokes equations in open flows where Dirichlet boundary condition (BC) for the pressure are given on part of the boundary is presented. The equations in primitive variables are solved using a projection method on a non-staggered grid with second-order...

An explicit numerical method to solve the unsteady incompressible flow equations consisting on N small time steps Δt between each two much larger time steps (Δt)1 is considered. The stability and efficiency of the method is first analyzed using the one-dimensional diffusion equation. It is shown that the use of a time step Δt slightly smaller than...

The amplification of the circulation in an axisymmetric and incompressible sink flow inside a cylindrical container is numerically analyzed as a function of the sink Reynolds number (Re). To that end, both infinitesimal and finite-amplitude perturbations of the azimuthal velocity are introduced upstream of the sink. It is shown that, for moderate a...

Radial and swirl velocity components in an axisymmetric sink flow inside a cylindrical container of variable aspect ratio H/R are measured using laser-Doppler anemometry. It is shown that a vortex, superimposed to the meridional sink flow, is formed when the Reynolds number based on the sink flow rate is above a critical value. Both clockwise and c...