Experimental and Numerical Analysis of the Flow Inside a Configuration Including an Axial Pump and a Tubular Exchanger

In centrifugal and axial pumps, the flow is characterized by a turbulent and complex behavior and also by physical mechanisms such as cavitation and pressure fluctuations that are mainly due to the strong interactions between the fixed and mobile parts and the operating conditions. These fluctuations are more important at the tip clearance and propagate upstream and downstream of the rotor. The control of the fluctuating signal amplitudes can be achieved by incrementing the distance between the components mentioned above. This paper presents experimental and numerical results concerning the operation of a configuration that includes an axial pump and a bundle of tubes that mimics the cool source of a heat exchanger. The pump used in the tests has a low solidity and two blades designed in forced vortex, the tip clearance is approximately 3.87% of tip radius. The experimental measures were carried out using a test bench built for this purpose at the DynFluid Laboratory which was accomodated conveniently with a variety of instruments. Firstly, the characteristic curves were drawn for the pump at 1500 rpm and then a set of measurements concerning the use of pressure sensors was done in order to recover for different flow rates the static pressure signals upstream and downstream the pump and the exchanger. The pressure fluctuations and the performance curve were compared to the numerical results. The numerical simulations were carried out by using a Fluent code, the URANS (Unsteady Reynolds Averaged Navier-Stokes) approach and the k-ω SST turbulence model were applied to solve the unsteady, incompressible and turbulent flow. To record the fluctuating pressure signal, virtual sensors were necessary and placed at the same positions as in the experiments

Experimental study of hydraulic transport of large particles in horizontal pipes

This article presents an experimental study of the hydraulic transport of very large solid particles (above 5 mm) in an horizontal pipe. Two specific masses are used for the solids. The solids are spheres that are large with respect to the diameter of the pipe (5, 10 and 15%) or real stones of arbitrary shapes but constant specific mass and a size distribution similar to the tested spherical beads. Finally, mixtures of size and / or specific mass are studied. The regimes are characterized with differential pressure measurements and visualizations. The results are compared to empirical models based on dimensionless numbers, together with 1D models that are based on mass and momentum balance. A model for the transport of large particles in vertical pipes is also proposed and tested on data available in the Literature, in order to compare the trends that are observed in the present experiments in a horizontal pipe to the trends predicted for a vertical pipe. The results show that the grain size and specific mass have a strong effect on the transition point between regimes with a stationary bed and dispersed flows. The pressure drops are moreover smaller for large particles in the horizontal part contrary to what occurs for vertical pipes, and to the predictions of the empirical correlations

High Accuracy Volume Flow Rate Measurement Using Vortex Counting

A prototype device for measuring the volumetric flow-rate by counting vortices has been designed and realized. It consists of a square-section pipe in which are placed a two-dimensional bluff body and a strain gauge force sensor. These two elements are separated from each other, unlike the majority of vortex apparatus currently available. The principle is based on the generation of a separated wake behind the bluff body. The volumetric flow-rate measurement is done by counting vortices using a flat plate placed in the wake and attached to the beam sensor. By optimizing the geometrical arrangement, the search for a significant signal has shown that it was possible to get a quasi-periodic signal, within a good range of flow rates so that its performances are well deduced. The repeatability of the value of the volume of fluid passed for every vortex shed is tested for a given flow and then the accuracy of the measuring device is determined. This quantity is the constant of the device and is called the digital volume (V_p). It has the dimension of a volume and varies with the confinement of the flow and with the Reynolds number. Therefore, a dimensionless quantity is introduced, the reduced digital volume (V_r) that takes into account the average speed in the contracted section downstream of the bluff body. The reduced digital volume is found to be independent of the confinement in a significant range of Reynolds numbers, which gives the device a good accuracy

Experimental study of yawed inflow around wind turbine rotor

In this article, we present an experimental study in a wind tunnel of a three-bladed, Rutland 503 model, horizontal axis yawed wind turbine. Power measurement and an exploration downstream wake of the turbine using particle image velocimetry measurements are performed. The variation of power coefficient as a function of rotational velocity is presented for different yaw angles. The results show a loss of power from the wind turbine when the yaw angle increases. The velocity field of the downstream wake of the rotor is presented in an azimuth plane, which passes through the symmetry axis of the rotor. The instantaneous velocity field is measured and recorded to allow for obtaining the averaged velocity field. The results also show variations in the wake downstream due to decelerating flow caused by the yawed turbine rotor. Analysis of this data shows that the active control of yaw angles could be an advantage to preserve the power from the wind turbine and that details near rotor wake are important for wake theories and topredict the performance of wind turbines as well

Experimental study of yawed inflow around wind turbine rotor

In this article, we present an experimental study in a wind tunnel of a three-bladed, Rutland 503 model, horizontal axis yawed wind turbine. Power measurement and an exploration downstream wake of the turbine using particle image velocimetry measurements are performed. The variation of power coefficient as a function of rotational velocity is presented for different yaw angles. The results show a loss of power from the wind turbine when the yaw angle increases. The velocity field of the downstream wake of the rotor is presented in an azimuth plane, which passes through the symmetry axis of the rotor. The instantaneous velocity field is measured and recorded to allow for obtaining the averaged velocity field. The results also show variations in the wake downstream due to decelerating flow caused by the yawed turbine rotor. Analysis of this data shows that the active control of yaw angles could be an advantage to preserve the power from the wind turbine and that details near rotor wake are important for wake theories and topredict the performance of wind turbines as well

Mixing in turbulent compressible heated coaxial jets: A numerical study

The computation of compressible coaxial jets has moved into the field of interest not only in fundamental research but also in industrial applications, especially in chemical engineering. Numerical simulations of such flows are performed here, using a code specifically developed for gaseous turbulent flows which can also take into account chemical reactions. The coaxial jet can be regarded as a model of injection device in industrial applications; one can cite combustion and aeroacoustics technology. Three-dimensional numerical simulations in this configuration, already published by various authors in open literature are limited to incompressible isothermal flow. In our work, we have explicitly taken into account the temperature gradient effects on the dynamics and mixing mechanisms. Indeed, we have investigated a spatially developing compressible (isothermal and non-isothermal coaxial jet). The numerical model is based on time and space resolutions of compressible Navier-Stokes equations. The piece wise parabolic method (PPM) is combined with a linearized Riemann solver. This scheme adds non-linear dissipation intermittently just where and when needed in order to avoid spurious oscillations and guarantee monotonicity for the advection equation. The simulation can, therefore, be regarded aslarge-Eddy simulations: large scales are accurately solved with minimal viscosity and non-linear dissipation extracts energy out of the small scales in order to avoid non-physica loscillations. In order to study the mixing between Air-Air flows, we consider the mixture fraction f to track the mixing between two species seeded in the coaxial jets. A great attention is paid to the spatial-temporal evolution of the mixture fraction f, with aparticular interest to probability density function. The comparison between the numerical results and experimental data is fairly good, with respect to the mean and turbulent fields. We found that the inner potential core length in the non-isothermal configuration reduced with respect to the isothermal coaxial jet due to the gradient of temperature. It was shown that in the non-isothermal coaxial jet, the temperature gradient leads to the rapid development of the inner Kelvin-Helmholtz vortices implying an efficient mixing of the species close to the exit of the computational domain

A naturally anti-diffusive compressible two phases Kapila model with boundedness preservation coupled to a high order finite volume solver

This paper presents a two phases flow model combined with a high order finite volume solver on unstructured mesh. The solver is highly conservative and preserves the sharpness of the interface without any reconstruction. Special care has been taken for boundedness preservation, as a high order scheme does not guaranty the boundedness of the volume fraction. The efficiency of the method is demonstrated with two numerical experiments: the simple advection test and the interaction between the shock and a bubble. Although experiments have been carried out with fine mesh, it is also demonstrated that the method allows satisfactory results to be obtained with coarse mesh

Improved δ-SPH Scheme With Automatic and Adaptive Numerical Dissipation

[Abstract] In this work we present a δ-Smoothed Particle Hydrodynamics (SPH) scheme for weakly compressible flows with automatic adaptive numerical dissipation. The resulting scheme is a meshless self-adaptive method, in which the introduced artificial dissipation is designed to increase the dissipation in zones where the flow is under-resolved by the numerical scheme, and to decrease it where dissipation is not required. The accuracy and robustness of the proposed methodology is tested by solving several numerical examples. Using the proposed scheme, we are able to recover the theoretical decay of kinetic energy, even where the flow is under-resolved in very coarse particle discretizations. Moreover, compared with the original δ-SPH scheme, the proposed method reduces the number of problem-dependent parameters.This research was funded by the Ministerio de Ciencia, Innovación y Universidades of the Spanish Government, grant number #RTI2018-093366-B-I00, by the Consellería de Educación e Ordenación Universitaria of the Xunta de Galicia (grant number #ED431C 2018/41). Xesús Nogueira has also been funded by the Xunta de Galicia through the program Axudas para a mellora, creación, recoñecemento e estruturación de agrupacións estratéxicas do Sistema Universitario de Galicia (grant number # ED431E 2018/11)Xunta de Galicia; ED431C 2018/41Xunta de Galicia; ED431E 2018/1