bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Analysis of a Bathtub Vortex in a Simplified Cowl Box of Automotive Vehicles
Authors: Recoquillon Yann , Andrès Emmanuelle , Kourta Azeddine 
Published: July 2013

On automotive vehicles, the cowl box is a volume located at the bottom of the windshield, under the cowl top grille. It provides external fresh air to the HVAC (Heating, Ventilating and Air Conditioning) unit and it is used to collect water coming from the windshield under rain conditions. This box is designed as a tranquillisation chamber to segregate water from air and avoid the ingress of rainwater into the HVAC unit. However, as the area is awkward to access with measuring devices, our knowledge about the physics of flow in the cowl box is limited.
The present work aims to advance our knowledge through experimental work on the air/water flow in a simplified cowl box in order to optimize the box size and improve numerical models. This paper will focus on the analysis of the bathtub vortex, which is potentially responsible for insufficient draining of the water collected in the cowl box.
The experimental set-up consists of a Plexiglas parallelepiped representing a simplified cowl box with top cowl grille, HVAC inlet and drain. A blower generates airflow through the HVAC inlet. A water sheet, with controlled flow rate, is created on an inclined plane representing the windshield. Velocity measurements of all components are obtained by PIV (Particle Image Velocimetry) in the liquid phase and the surface level is recorded by a capacitance probe near the drain. Moreover, contour detection of the vortex core is achieved using a high-speed camera. Results show a relationship between the pressure loss generated by the airflow in the cowl box, the water level and the vortex structure. The modification of the vortex structure as well as the modification of velocity components near the air core are visible only in transient stages. These experimental results give us today some insight to understand the physical phenomena occurring in the cowl box.
Monte Carlo Simulations of Micro-Particle Detachment and Resuspension From Surfaces in Turbulent Flows
Authors: Goldasteh Iman , Ahmadi Goodarz , Ferro Andrea 
Published: July 2013

Micro-particle adhesion, detachment and resuspension from surfaces have attracted considerable attention due to their numerous applications in semiconductor, xerographic, and pharmaceutical industries, and, more recently, in understanding indoor air quality. However, most earlier studies have focused on idealized spherical particles and smooth surfaces, and the effects of particle irregularities and surface roughness on the rate of particle removal and resuspension are not well understood. In this work, a Monte Carlo simulation of particle resuspension from a surface under turbulent flow conditions was developed and resuspension of nearly spherical and irregular shaped particles with rough surfaces from substrates under turbulent flow condition was studied. Following our earlier approach, compact irregular shaped particles were modeled as spherical particles with a number of hemispherical bumps. It was assumed that the bump surfaces also have fine roughness. The extended Johnson-Kendall-Roberts (JKR) adhesion theory for rough surfaces was used to model the particle adhesion and detachment.
A number of assumptions were made to apply the model. It was assumed that the particles have a Gaussian size distribution. The number of bumps of the irregular particles and surface roughness values of particle are assumed to be random, respectively, with Poisson and log-normal distributions. For particle detachment from the surface, the theory of critical moment was used. The effects of particle size, turbulent flow, particle irregularity and surface roughness on particle detachment and resuspension were studied for different cases. The Monte Carlo model predictions show probabilistic distributions of the particle resuspension. The simulation results are compared with the available experimental data and good agreement was found. The study provided information on the random nature of particle resuspension due to the randomness in the airflow, particle size distribution and surface roughness.
Numerical Investigation of Viscous Flow in Three Centrifugal Pumps
Authors: Moreno Carlos Luis , Fuenmayor Alejandro , Núñez Gilberto , De Andrade Jesús , Noguera Ricardo , Asuaje Miguel 
Published: July 2013

Centrifugal pump performance is affected when pumping viscous liquids, requiring a larger power input than the same pump handling water. In applications of chemical, civil, environmental, and mechanical engineering that involve centrifugal pumps, it is a challenge to accurately estimate and even more of a challenge to improve their performance when handling viscous liquids. When accurate performance data is needed, difficult experiments must be conducted with the operating viscous flow. The extension of the applicability of numerical techniques for solving fluid dynamics (CFD) permits the consideration of these tools as a definite possibility for predicting the performance of centrifugal pumps with viscous flows. The purpose of this study is to perform a 3D-CFD steady-state simulation of three different configurations of centrifugal pumps. The first is an impeller-diffuser pump (ns = 19) taken from an ESP model. The second is a Francis Pump-Turbine (ns = 28). Finally, the third configuration possesses an impeller and volute (ns = 32). The objective is to characterize and evaluate their performances with four different fluids from 1 to 420 cSt. These are: water at 25°C, SAE10 and SAE30 oils, and Fuel Oil Medium (FOM). For water flow conditions, the numerical results were compared with experimental data, and found to be consistent with global performance parameters. With regard to the higher viscosity fluids, the CFD calculation was compared with those obtained through the standard empirical method (ANSI/HI9.6.7). This resulted in good agreement between the performance results. The commercial software ANSYS-CFX was used for the CFD calculations.
The resulting pump performance curve (head, hydraulic efficiency and power output) is consistent with that expected by theory. In general, as the viscosity of fluids increases, the hydraulic energy losses increase. Of the three pumps, slip factor for SAE30 oil was larger for all volumetric flows since it features the best guidance of the flow in the impeller blade passage. For the ns32 pump and the pump-turbine ns28, the volute losses rose from water to FOM, just like the impeller hydraulic losses. For these two turbo machines, the impeller losses were larger than volute losses. For the pumps with volute, the effects of fluid viscosity on the radial forces were evaluated. It was found that the radial forces decrease when the viscosity increases. This paper attempts to contribute to a better understanding of fluid dynamics within centrifugal pump impellers handling viscous fluids, and intends to shed more light on the approaches that performance prediction models should follow in the future.
Use of Lattice-Boltzmann Method in Mass Transfer for the Wall Shear Stress Calculation in an Unsteady Laminar Flow Downstream of a Cylinder Located in a 2D Rectangular Channel
Authors: Abassi Wafik , Aloui Fethi , Ben Nasrallah Sassi , Legrand Jack 
Published: July 2013

A Lattice Boltzmann method (LBM) is proposed to study the flow and mass transfer in the parietal zone of a channel containing a blocking circular obstacle at low Reynolds number. For such configuration, the variation of Re based on cylinder diameter leads to different regime that fluid may occur during it flowing. Hence, this varied behaviour of flow downstream of the obstacle affects the mass transfer rate in the parietal zone of the channel.
A sensor with zero concentration on the surface is placed at different locations on the channel wall downstream of the cylinder. Flow velocity and concentration profile of diffusing species on the sensor were evaluated and analyzed for different Reynolds. The Sherwood numbers are calculated and compared with available experimental data.
For the present simulation, LBM is based on the D2Q9 lattice model and the single relaxation time approach called BGK method.
The challenge of this work is to extend the use of the mesoscopic method (LBM) for a flow problem to studying the enhancement of the rate of mass transfer to channel wall downstream of the obstacle. The numerical results are in good agreement with the benchmark result available in the literature. The highlight of calculation is the flexibility to deal with the boundary conditions for such a problem.
The result indicates that LBM is useful for simulation of fluid flows with mass transfer as well as heat transfer.
On the Stability of Taylor - Couette Flow With Axial Flow
Authors: Berrich Emna , Aloui Fethi , Legrand Jack 
Published: July 2013

An experimental investigation of Taylor-Couette flows with axial flow is presented. Two techniques are used: Visualization using the Kalliroscope and Electro-diffusion method using electrochemical probes. The fluid is confined between concentric cylinders. It is constituted by an electrochemical solution seeding with 2% of a rheoscopic liquid AQ-1000 (Kalliroscope Corp., U.S.A.). The rheoscopic liquid contains small particles reflecting light in dependence on their orientation imposed by the flow direction. The reflected light intensity of Kalliroscope flakes allows a qualitative study of the flow. While the polarography technique allows the measurement of diffusion limit current intensities delivered by the electrochemical probes. The frequency responses of the probe to the flow allow the determination of the instantaneous and local mass transfer and the instantaneous wall shear rate.
Two protocols were adopted to study the effect of an axial flow superposed to Couette-Taylor flows and the history flow effect. The first one consists to impose an azimuthal flow to the inner cylinder. When the regime was established, we superposed the axial flow. This protocol was named “the direct protocol”. While the second protocol consists to impose firstly the axial flow on the gap of the system then the azimuthal flow. We named it “the inverse protocol”. We demonstrated that the Couette-Taylor flow with axial flow is strongly dependent on the flow history (the protocol). For the same Taylor number and axial Reynolds number, the resulting flow is completely different. An axial flow superposed to Couette-Taylor flow can delay the instabilities apparition; generate the displacement of the Taylor vortices in the same direction as the axial flow or in the opposite direction; and modify the instability character of the flow by developing helical vortices or wavy helical vortices.
A Practical Approach to Speed Up NPSHr Prediction of Centrifugal Pumps Using CFD Cavitation Model
Authors: Ding H. , Visser F. C. , Jiang Y. 
Published: July 2013

This paper presents an innovative NPSHr prediction procedure. Derived through analyzing the definition of NPSHr and the characteristics of pump head vs. NPSH curve (i.e. head drop curve), this procedure can significantly reduce the number of simulations needed in NPSHr prediction. For the majority of cases, NPSHr can be predicted with reasonable accuracy for one flow rate in as little as three simulation runs. This procedure is also very robust since it can avoid running simulations under severe cavitation conditions. Therefore simulation convergence is improved and simulation time is reduced for each simulation step.
In the paper, the methodology of the proposed approach is derived and explained. The complete procedure with suggested strategies is laid out in detail. Then the procedure is demonstrated against an industrial pump case. NPSHr prediction results are compared with experimental data. Important factors which can affect NPSHr prediction are also indentified and discussed.
Predicting Bubble Migration due to Bjerknes Force in a Complex 3D Geometry: Numerical and Experimental Results
Authors: Valentin Francisco I. , Cancelos Silvina 
Published: July 2013

While the Bjerknes force is not the only force experienced by a bubble subjected to an acoustic field; studies of bubble translation in non-flowing fluid have identified Bjerknes force as being the most influential. Therefore, Bjerknes force can be used to trap bubbles in predefined locations of maximum and minimum absolute pressure. Specifically challenging is to determine these locations in complex geometries because direct measurement of the acoustic pressure for the whole system is generally not possible. The objective of this research is to numerically predict Bjerknes force effect on bubble migration and accumulation in a complex 3D geometry that includes piezoelectric materials, elastic materials and a fluid media.
A numerical solution of the acoustic pressure field was obtained for this geometry, valid in the range of small pressure oscillations. Additionally, using the linearized Rayleigh-Plesset equation, which gives the volumetric oscillations of a bubble subjected to an acoustic field, the Bjerknes force was numerically computed. By knowing the Bjerknes force, a bubble migration pattern upon entering the system was predicted. A CMOS high speed camera was used to experimentally monitor bubble multimode excitation and bubble response to a stationary pressure field validating our numerical results. Results are presented for experiments conducted for a 1mm bubble diameter with acoustic fields ranging from 7 to 10 kHz which correspond to values of the structure and/or the bubble’s resonant frequency.
Entropy Generation in Laminar Flow Junctions
Authors: Sanchez Mauricio , Henderson Andrew W. , Papavassiliou Dimitrios V. , Lemley Evan C. 
Published: July 2013

Laminar flow dominates microscale and milliscale applications. This work is focused on laminar energy losses in junctions (bifurcations). Reynolds number plays a dominant role in energy losses for laminar flow. The physical cause of these energy losses is entropy generation. This paper analyzes the energy losses in junctions by considering the entropy generation.
This paper documents results from computational fluid dynamics (CFD) simulations of laminar flow in planar junctions. The junctions studied consisted of circular pipes with two outlets and one inlet tube with Reynolds numbers ranging from one to 1000. A general technique has been developed to produce computer models of junctions in which the inlet tube size is set, but the outlets are allowed to vary in size and angle relative to the inlet tube. A generalized algorithm has been implemented to create three-dimensional models of the junctions for both computational and experimental studies. The entropy generation has been determined in junctions from simulation results for the velocity field. Results for entropy generation as a function of geometry and Reynolds are presented. Energy loss coefficients are derived from the simulations and compared to experimental measurements of energy losses in microscale junctions.
Influence of a Diffuser to the Wake Flow of a Passenger Car
Authors: Marklund Jesper , Lofdahl Lennart 
Published: July 2013

To achieve more energy efficient transportation we have to reduce losses and resistance forces all over the vehicle. Aerodynamic drag is one of the primary resistance forces a passenger vehicle has to overcome and the force increases exponentially with increased speed. The under-body and rear-end geometry of a passenger car is a significant contributor to the overall aerodynamic drag and the shape of it is normally a compromise between styling, cost and other properties. To reduce the aerodynamic drag it is very important to have a good pressure recovery at the rear-end; to end up with a base pressure as high as possible. It is not necessarily the case that an optimized lower part of the rear-end for a square-back car has the same performance as a notch-back or fast-back car.
This work investigates the rear-end flow and aerodynamic performance of a sedan and wagon car with varying rear-end under-body design parameters. The study is a numerical analysis using a standard CFD approach commonly used in the automotive industry. A parameter study of under-body covers with varying rear angles, making the rear floor act like a diffuser. The function of the rear floor working as a diffuser is similar regardless of the upper geometry, but its function as a drag reduction device can be very different. Results from this study show a potential to reduce aerodynamic drag of the sedan car approximately 10%, with the best diffuser angle and cover plates over the floor. The best drag reduction for the wagon car was 2–3% and the optimum was at a smaller diffuser angle. Flow analysis of the wake shows how important it is the wake is balanced.
On the Interaction of Boundary Layer and Mixing Layer in Stratified Pipe Flow
Authors: Merzari Elia , Fischer Paul , Pointer W. David , Pellegrini Marco , Ninokata Hisashi 
Published: July 2013

Stratified pipe flow in a pipe has been the subject of several investigations over the years. In fact it is relevant to the operation of thermal energy systems involving significant temperature gradients and low flow conditions. Stratification affects mixing, and is one the key phenomena that need to be addressed in the design of any mixing system of devices involving significant density difference. In order for thermal stratification in a pipe to be correctly modeled the underlying hydrodynamic behavior related to the mixing of two streams in a pipe needs to be fully understood.
The present paper deals with the numerical simulation of the flow in a pipe where the bottom half has a lower velocity compared to the upper half. A turbulent mixing layer develops in the streamwise direction at the interface between low flow region and higher flow region. Since the Reynolds number is low, the boundary layer and the mixing layer are about the same size. This translates in non trivial interactions between the structures in the boundary layer and the mixing layer. The failure of RANS models in accounting for the mixing points in this direction.
An LES of the flow in this geometry has been performed with the spectral code Nek5000. The averaged statistics have been compared with available experimental results. Proper Orthogonal Decomposition has been applied to clarify outstanding issues in RANS modeling.
An Eulerian Method for Water Droplet Impingement by Means of an Immersed Boundary Technique
Authors: Capizzano F. , Iuliano E. 
Published: July 2013

The estimation of water droplet impingement is the first step for a complete ice-accretion assessment. Basically two different numerical approaches can be found in literature: the Lagrangian and the Eulerian methods. The present paper describes the design and development of a water impingement simulation tool based on Eulerian droplet equations solved on Cartesian meshes by using an immersed boundary (IB) technique.
The robustness of the methodology and the accuracy of the approach are discussed. The method is applying to classical two- and three-dimensional test-cases for which experimental data are available in literature. The results will be discussed by comparing with experimental and body-fitted numerical solutions.
Influence of Bubbles on the Turbulence Anisotropy
Authors: Bolotnov Igor A. 
Published: July 2013

Direct numerical simulations (DNS) with interface tracking of turbulent bubbly flows are becoming a major tool in advancing our knowledge in the multiphase modeling research area. Comprehensive analysis of turbulent flow structure allows to evaluate the state-of-the-art computational multiphase fluid dynamics (CMFD) models and to propose new closure laws.
The presented research will demonstrate how the multiphase DNS data can inform the development of computational fluid dynamics (CFD) models. In particular, Reynolds stress distribution will be evaluated for single and two-phase bubbly flows and the level of turbulence anisotropy will be measured in several scenarios. The results will help determine if the isotropic turbulent models are suitable for bubbly flow applications or there is a strong need to apply and develop Reynolds-stress turbulent models for two-phase flow CFD modeling.
Characterization of Liquid Sheet Breakup Using Numerical Experiments
Authors: Sinclair Jarrod , Abanteriba Sylvester 
Published: July 2013

For the plain orifice nozzle configuration, breakup mode analysis of the issuing liquid jet has been extensively, over the years, undertaken. The works of Rayleigh, Haenlein, Ohnesorge, Reitz and others have used an Ohnesorge-Reynolds chart to clearly characterize breakup into four distinct modes. These include: (1) Rayleigh, (2) first wind induced, (3) second wind induced, and (4) prompt atomization. Planar liquid sheet flows have not undergone such intensive characterization analysis. In this work a non-expanding (nor thinning) liquid sheet is injected into a quiescent volume of gas from a planar nozzle of constant opening height. The flow has no co-flowing gas stream nor air-assistance to drive the disintegration. The nozzle configuration and subsequent liquid primary breakup is somewhat similar to an outward opening fuel injector having an annular outlet with a large radius to needle lift height ratio.
The numerical experiments in this work use a high fidelity Computational Fluid Dynamics (CFD) modeling approach. This includes the Volume-Of-Fluid (VOF) two-phase method to represent the liquid and gas fluids both considered to be incompressible, coupled with the Large Eddy Simulation (LES) treatment of turbulence modeling. The initial primary breakup of the liquid sheet into large droplets, ligaments and other structures is the main focus of the modeling. As such, secondary breakup and possible evaporation of the liquid is not considered. Due to the configuration of the planar nozzle, upstream cavitation of the liquid within the nozzle is also not considered.
Breakup studies were conducted within the Reynolds number range of 3,000 to 23,400, and Ohnesorge number range of 0.004 to 0.1. Results are extensively validated with the works of Heukelbach and Scholz. In-nozzle velocity profiles are characterized with Reynolds number showing laminar, semi- and fully-turbulent states in the flow boundary layer and core. Velocity profile relaxation is studied as the liquid sheet transitions from a wall-bounded flow within the nozzle to a free shear flow surrounded by gas. Particularly, the axial velocity component is seen to weaken, whilst the sheet normal velocity component strengthens and aids in disintegration of the liquid sheet.
Flow Characteristics of a Three Dimensional Bluff Body With a Single Rotating Cylinder
Authors: Bell James R. , Burton David , McArthur Damien , Sheridan John 
Published: July 2013

This work investigated the application of a rotating cylinder to the upper leeward edge of a three dimensional bluff body in ground proximity.
Aerodynamic drag measurements, base pressure contours and wake velocity profiles were obtained in a closed jet wind tunnel for Reynolds Numbers in the range of approximately 220,000 to 660,000. The cylinder of diameter 0.1H was mounted on the upper edge of the leeward face of the body. The ratio of cylinder surface velocity to freestream velocity was varied from 0 to 2.0. A computational model of the geometry was developed and results are presented for various velocity ratios and cylinder diameters.
The results of this work demonstrated that, even at low velocity ratios, the cylinder rotation has a large effect on the flow structures in the body wake region. A large downwash is observed that creates two large counter-rotating vortices and a resultant significant increase in drag.
The aerodynamic drag changes are presented as a function of velocity ratio and are shown to be Reynolds Number insensitive over the range tested. Aerodynamic drag was shown to increase with increasing velocity ratio over the velocity ratio range 0.25 to 2.0.