Laser Doppler Anemometer Measurements Research Articles

A numerical method to mimic an experimental wind gust generator: The immersed boundary gust generator

To generate horizontal wind gusts in a classical wind tunnel, Wood, Breuer, and Neumann [A novel approach for artificially generating horizontal wind gusts based on a movable plate: The paddle,” J. Wind Eng. Ind. Aerodyn. 230, 105170 (2022)] developed a new wind gust generator denoted the “paddle.” The working principle relies on the partial blocking of the outlet of the wind tunnel nozzle by a plate that vertically moves into the free-stream. Based on laser-Doppler anemometer measurements of the velocity at only a few locations, the basic functionality of the device was proven. The objective of the present contribution is to numerically mimic the gust generator and the flow field induced by the paddle in the test section. Contrary to the single-point measurements, the three-dimensional time-resolved simulation delivers the entire flow field and thus allows to investigate all details of the generated gust. To describe the paddle motion, the immersed boundary method with a continuous and direct forcing approach is implemented into a finite-volume flow solver for large-eddy simulations. A uniform and a non-uniform distribution of the Lagrangian markers are investigated where the latter ensures that an excessive increase in the computational resources required can be avoided. The predictions allow to characterize the resulting flow features induced by the paddle in great detail. Furthermore, a comparison of the numerical and experimental results is carried out based on the time histories of the streamwise and vertical velocity components at certain positions showing a close agreement. Finally, the forces acting on the fluid by the moving paddle are evaluated.

Noise induced effects in the axisymmetric spherical Couette flow.

We study the axisymmetric, wide gap, spherical Couette flow in the presence of noise in numerical simulations and experiments. Such studies are important because most of the flows in nature are subjected to random fluctuations. Noise is introduced into the flow by adding fluctuations to the inner sphere rotation which are random in time with zero mean. Flows of a viscous incompressible fluid are induced either by rotation of the inner sphere only or by the co-rotation of the spheres. Mean flow generation was found to occur under the action of additive noise. A higher relative amplification of meridional kinetic energy compared to the azimuthal component was also observed under certain conditions. Calculated flow velocities were validated by laser Doppler anemometer measurements. A model is proposed to elucidate the rapid growth of meridional kinetic energy for flows induced by varying the co-rotation of the spheres. Our linear stability analysis for flows induced by the rotation of the inner sphere revealed a decrease in the critical Reynolds number, corresponding to the onset of the first instability. Also, in this case, a local minimum of the mean flow generation on approaching the critical Reynolds number was observed, which is consistent with the available theoretical predictions. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (Part 2)'.

Flow around surface-mounted permeable cubes on solid and deformable surfaces

A wind tunnel experiment was carried out to characterize the flow surrounding rectangular prisms of varying permeability, each set mounted on a stationary plane-bed surface and subsequently on an erodible bed. Laser-Doppler anemometer measurements of the horizontal and vertical velocity components were obtained in a grid that included an area adjacent to the windward face, enveloped the free end of the form, and extended ≈6.5 element heights downwind of the rear wall. From these component measurements, the total velocity (Tuw), turbulence intensity (TI), Reynold Stress (RS) and the turbulence kinetic energy (TKE) were calculated throughout the sampling array. As compared to an impermeable same-sized cube, the near-surface TKE and RS were substantially reduced within the wake flow behind the permeable elements. In the plane-bed experiments, TI generally increased downwind of the permeable cubes, opposite to the trend for the impermeable form. The distinction in TI was less pronounced, however, when the bed morphology developed scour marks. The impermeable cube had the largest amount of erosion relative to its volume, in response to strong downwash along its windward face and the development of an energetic horseshoe vortex. This coherent flow structure was not detected for all permeable forms and the amount of scour was orders of magnitude less. This study would suggest that for restricting erosion, the efficiency of a surface-mounted element can be improved by making the walls of the form permeable rather than solid, thereby increasing energy dissipation in the wake flow while reducing vortex impingement and bed shear stress.

Flow around Surface-Mounted Permeable Cubes on Solid Surfaces

A wind tunnel experiment was administered to characterize the flow surrounding rectangular prisms of varying permeability, each set mounted on a stationary plane-bed surface and subsequently on an erodible bed. Laser-Doppler anemometer measurements of the horizontal and vertical velocity components were obtained during a grid that included a neighbourhood adjacent to the windward face, enveloped the free end of the shape, and extended ≈6.5 element heights downwind of the rear wall. From these component measurements, the entire velocity (Tuw), turbulence intensity (TI), Reynold Stress (RS) and therefore the turbulence K.E. (TKE) were calculated throughout the sampling array. As compared to an impermeable same-sized cube, the near-surface TKE and RS were substantially reduced within the wake flow behind the permeable elements. Within the plane-bed experiments, TI generally increased downwind of the permeable cubes, opposite to the trend for the impermeable form. The excellence in TI was less pronounced, however, when the bed morphology developed scour marks. The impermeable cube had the most important amount of abrasion relative to its volume, in response to strong downwash along its windward face and therefore the development of an active horseshoe vortex. This coherent flow structure wasn't detected for all permeable forms and therefore the amount of scour was orders of magnitude less. This study would suggest that for restricting erosion, the efficiency of a surface-mounted element are often improved by making the walls of the shape permeable instead of solid, thereby increasing energy dissipation within the wake flow while reducing vortex impingement and bed shear stress. The study of the flow around surface-mounted, sharp-edged obstacles placed in a channel is fundamental to the understanding of the flow mechanisms for complex two- and three dimensional geometries. There exists a considerable amount of published data for flows over two-dimensional geometries such as ribs and fences. However, there are markedly fewer studies in the literature concerned with the flow around three dimensional obstacles. Of these, most are limited to the study of a single parameter, for example, the reattachment length. It is therefore the aim of this study to provide a general description of the flow around three-dimensional obstacles. Based on the flow visualization experiments performed for obstacles of different aspect ratio (width-to-height), the changes in the flow patterns as a function of aspect ratio are discussed qualitatively. Additionally, large-scale parameters such as the reattachment and separation lengths are discussed quantitatively. The flow around single, surface-mounted, prismatic obstacles submerged in a boundary layer at high Reynolds numbers depends on a large number of parameters.

High-frequency simultaneous measurements of velocity and concentration within turbulent flows in wind-tunnel experiments

We analyse the metrological aspect related to systems devoted to the simultaneous measurements of (one point) velocity and scalar concentration statistics. We consider systems based on the coupling of an anemometer (laser Doppler or hot wire) with a flame ionization detector. In particular, we focus on the estimate of the cross-correlation velocity-concentration. Key aspects in the reliability of such measurements are related to the identification of an optimal distance between the two probes, the time lag with which the velocity and concentration signals are acquired, and, eventually, the influence of seeding particles (when using a laser Doppler anemometer) on the concentration measurements. We investigate these aspects by performing wind-tunnel experiments on the scalar dispersion downwind a ground-level source in a turbulent boundary layer. This analysis allowed us to identify a time delay and a convenient distance between the signals provided by the anemometer and the concentration detector. Results also show that the seeding used for the laser Doppler anemometer measurements modifies the cut-off frequency in the concentration spectra and induces a slightly larger uncertainty on the statistics of scalar field. The results show the reliability of both systems in estimating (horizontal and vertical) turbulent mass fluxes.

Mapping of the turbulent round jet developing region using a constant temperature anemometer (CTA)

The fully developed round turbulent jet has been extensively studied, whereas the developing region is much less understood. The high shear and turbulence intensities in the most interesting parts of the developing region make them inaccessible to common measurement techniques such as Constant Temperature Anemometry (CTA) due to the high demands on the measurement techniques for accuracy of the measurements. Turbulence measurements are therefore planned using our in-house laser Doppler anemometer (LDA) system based on its capability to provide accurate measurements and with its inherent ability to properly distinguish velocity components. A rigorous measurement with the intended LDA system however demands impractical processing time, so knowing the critical points at which measurement are to be taken will save valuable time. This information is herein acquired significantly faster and more practically, however less accurately, with single-wire CTA. A high-resolution measurement was done using a computer-controlled single-wire CTA with the wire probe mounted perpendicular to the incoming flow from the jet orifice. The measurements covered several points in the radial (r-direction) along x/D=10, x/D=15, x/D=20 and x/D=30 downstream (where D is the jet exit diameter), with spatial resolutions ranging from 1 to 3 mm between the points, depending on how far the measurement was from the jet centerline. A proper alignment was also conducted prior to measurement so that the same points can be reached again for LDA measurement on the same jet afterwards. The radial profiles of mean velocity and turbulence intensity at each downstream position are presented to show the statistics of the air flow inside and outside the jet. As expected from theory, the mean profiles display a nearly Gaussian shape, spread out and tapered with the downstream direction. The highest velocities are located at the centerline.

Formation of high quality interference fringes from both sides of a suitably designed hololens in the laser Doppler anemometer measurement volume

We report, for the first time to the best of our knowledge, the formation of high quality, evenly spaced, undistorted fringes in the measurement volume of a laser Doppler anemometer from both sides of a suitably designed hololens. Experiments are performed for the analysis of fringes formed at the measurement volume by real time monitoring and actual fringe field analysis techniques. The results indicate the qualitative as well as quantitative improvement of 66.58 % in overall average normalised standard deviations of the width of the fringes formed by the proposed imaging configuration than that of the conventional imaging configuration.

Multi-species PLIF study of the structures of turbulent premixed methane/air jet flames in the flamelet and thin-reaction zones regimes

Simultaneously planar laser-induced fluorescence (PLIF) measurements of OH, CH, CH2O and toluene are carried out to investigate the structures of turbulent premixed methane/air jet flames in the flamelet regime and the thin-reaction zones regime. A premixed flame jet burner of an inner diameter of 1.5mm is employed. Stoichiometric methane/air mixtures introduced as a jet are ignited and stabilized in a hot co-flow generated by a coaxial porous plug pilot flame surrounding the jet. The Reynolds number for the studied jet ranges from 960 to 11,500 with the characteristic Karlovitz number ranging from 1 to 60. The focus of this study is on the characterization of the structures and turbulent burning velocity of premixed flames in the flamelet and the thin-reaction zones regimes. The preheat zone is analyzed using the CH2O and toluene PLIF fields, whereas the reaction zone is analyzed using the CH and OH PLIF fields. Laser Doppler Anemometer (LDA) measurements are performed to characterize the turbulence field and it is noted that when the Reynolds/Karlovitz number increases a successive thickening of the preheat zone is observed, whereas the reaction zone, characterized by the CH layer maintains nearly the same thickness. The heat release zone, characterized by the combination of the OH and CH2O PLIF fields, is shown to nearly maintain the same thickness under the present experimental conditions. The flame surface wrinkle ratio is shown to be Reynolds number and Karlovitz number independent when the Reynolds number is high enough such that the smallest wrinkle scales reach to the length scales of the thin reaction layers. The global fuel consumption speed of the jet flame is analyzed using the toluene PLIF field and the OH PLIF field. A discrepancy in the two consumption velocities is found as the Karlovitz number increases. This is found to be a result of the broadening of the oxidation zone. These findings provide experimental support to the flamelet and thin-reaction zone regime hypotheses of turbulent premixed combustion.

A wind tunnel study of flow structure adjustment on deformable sand beds containing a surface‐mounted obstacle

AbstractRoughness elements of varied scale and geometry commonly appear on the surfaces of sedimentary deposits in a wide range of planetary environments. They perturb the local fluid flow so that the entrainment, transport, and deposition of particles surrounding each element are fundamentally altered. Fluid dynamists have expended much effort in examining the flow structures surrounding idealized elements mounted on fixed, planar walls. However self‐regulation occurs in sedimentary systems as a result of the bed surface undergoing rapid topographic modification with sediment transport, until it reaches a stable form that enhances the net physical roughness. The present wind tunnel study examines how the flow pattern surrounding an isolated cylinder, a problem extensively studied in classical fluid mechanics, is altered through morphodynamic development of a deep well that envelopes the windward face and sidewalls of the roughness element. Spatial patterns in the fluid velocity, turbulence intensity, and Reynolds stress obtained from laser Doppler anemometer measurements suggest that the flow structures surrounding such a cylinder are fundamentally altered through self‐regulation of the bed topography as it reaches steady state. For example, flow stagnation and the turbulent dissipation of momentum are substantially increased at selected points surrounding the upwind face and sidewalls of the cylinder, respectively. Along the center line of the wake flow to the rear of the cylinder, several structures arising from flow separation are annihilated by strong upwelling of the airflow exhausted from the terminus of the well. Feedback plays a complex, time‐dependent role in this system.

Enhanced Computational Fluid Dynamics Modeling and Laser Doppler Anemometer Measurements for the Air-Flow in an Aero-engine Front Bearing Chamber—Part I

Modern aero-engine development requires also a gradual increase in the overall effectiveness of lubrication systems. This particularly applies to bearing chambers where a complex two-phase flow is formed by the interaction of the sealing air and the lubrication oil. It is important to increase the level of understanding of the flow field inside the bearing chamber and to develop engineering tools in order to optimize its design and improve its performance. To achieve this, an experimental and a computational study of the whole front bearing chamber were carried out for a range of shaft rotational speeds and sealing air mass flow. The experimental measurements of the air velocity inside the chamber were carried out using a laser Doppler anemometer (LDA) in two-phase air/oil-flow conditions. The experimental facility is a 1:1 scale model of the front bearing chamber of an aero-engine. Computational 3D modeling of the bearing chamber was performed. The bearing gap and the presence of lubrication oil were modeled as an anisotropic porous medium with functions relating the pressure loss of the air coming through the gap and the tangential component of velocity of the air exiting the gap of the ball bearing with the air-flow rate through the gap and the rotational speed of the shaft. The methodology to obtain the above mentioned functions and the results of the detailed study are given (Aidarinis, J., and Goulas, A., 2014, “Enhanced CFD Modeling and LDA Measurements for the Air-Flow in an Aero Engine Front Bearing Chamber: Part II,” ASME Paper No. GT2014-26062). The enhanced computational model of the chamber implementing the law of pressure drop of the “lubricated” bearing and the function of modeling the tangential velocity of the air exiting the bearing was used to calculate the flow field for the full range of the measurements. A limiting curve dividing the operational map of the bearing chamber into two areas was predicted. Large vortical and swirling structures dominate the flow and they vary in size according to the position of the operation point relative to the limiting curve. Operation above the limiting curve leads to flow classified as type I with air going through the ball bearing while for operation below the limiting curve line the flow is classified as type II, there is no air-flow through the bearing gap.

Enhanced Computational Fluid Dynamics Modeling and Laser Doppler Anemometer Measurements for the Air-Flow in an Aero-engine Front Bearing Chamber—Part II

A detailed computational study of the air-flow through the outer gap of the front bearing of an aero-engine is presented. The reason to carry out this study was to understand the flow through the bearing as a function of the operational parameters of the engine, which was necessary for the modeling of the flow in the whole bearing chamber. The complex geometry and the size of the bearing gap relative to the overall dimensions of the bearing chamber and the need for very precise and detailed information of the effect on the flow within the chamber of the bearing operational parameters, prohibited the solution of the flow through the gap together with the rest of the bearing chamber. A 3D modeling of the flow through the outer bearing gap, which included a section of the ball bearing, was performed. Functions relating the pressure drop of the air coming through the bearing gap and the tangential component of velocity of the air exiting the bearing region, to the mass of air through the gap of the ball bearing and the rotational speed of the shaft were developed. The effect of the lubrication oil within the bearing was modeled as an anisotropic porous medium with a predefined law. In order to acquire in a mathematical form the above relationships a series of computational runs were performed. These relationships, in the form of second order curves, were subsequently introduced to the model of the bearing chamber as described by Aidarinis and Goulas (2014, “Enhanced CFD Modeling and LDA Measurements for the Air-Flow in an Aero Engine Front Bearing Chamber (Part I),” ASME Paper No. GT2014-26060). The constants of the relationships were derived through comparisons of the calculations with the experimental data. From the analysis, it was concluded that the pressure drop across the bearing increases with the square of the rotational speed of the shaft with the mass flow of air through the ball bearing as a parameter and vice versa. For this particular ball bearing, there is a region where, for any combination of rotational speed of the shaft and pressure drop through the bearing, there is no flow of air through the bearing. In this paper the detailed modeling methodology, the computational flow field, the boundary conditions and finally the results are presented and discussed.

Analysis of eddy viscosity models in predicting flow field of high-speed water jet

Three commonly used two-equation turbulence models were adopted. The computed velocity field was compared with the data from corresponding laser Doppler anemometer measurement to analyze the accuracy of these models. By adjusting the model parameters, the simulation data can fit into the experimental result. The optimal viscosity coefficients Cμ in these used eddy viscosity models were presented. It is shown that the RNG k-e model is more sensitive to Cμ, while the results from Standard k-e model vary almost linearly with the change of the Cμ value. Study on the simulated flow field gives that if the peak of turbulence kinetic energy appears within the radial span, it will affect the velocity distribution along the jet axis; otherwise, it will modify the velocity magnitude. The proposed numerical scheme reduces the physical complexities involved in ultra-high pressure injection process so that it can be applied to archive fast production from relevant CAE workflow.

Characteristics of Secondary Flow Induced by 90-Degree Elbow in Turbulent Pipe Flow

The purpose of this study is to characterize the swirling secondary flow in the downstream of a pipe bend using a numerical simulation of the flow. The CFD (Computational Fluid Dynamics) software OpenFOAM is used to simulate the turbulent flow in pipes with elbow. Various turbulence models are benchmarked with the existing experimental data and a comparative study is performed to select an appropriate turbulence model for the analysis. Predictions made by the selected turbulence model are compared with the LDA (Laser Doppler anemometer) measurements from the experiments currently conducted to find the dependency of the flows on the Reynolds number. It is found that the swirl intensity of the secondary flow is a strong function of the radius of curvature of the bend and a weak function of the Reynolds number. Additionally, it is found that the dissipation of the swirl intensity is exponential in nature.

Turbulent flow downstream of a large solidity perforated plate: near-field characteristics of interacting jets

Measurements of streamwise velocity characteristics in a flow downstream of a perforated plate with 96% solidity were obtained using a single-component laser Doppler system. The channel bulk velocity was 1 m s−1, the diameter D of the holes was 5 mm and the Reynolds number of the flow through the holes was around 10 000. The results are presented in terms of profiles of the mean and rms of streamwise velocity, their decay behaviour on the jet centre line, probability density functions (PDFs) of velocity fluctuations, velocity autocorrelation functions and integral time scales. In comparison with the literature data, the mean velocity decay on the centre line was much larger than that for a free jet but smaller than that for a confined jet. There was a mean reverse flow between the jets, and instantaneous reverse flow events were found also on the centre line of the jets. These were quantified based on the PDF of velocities, and at streamwise position x/D = 12 around 5% of the flow events on the centre line of the jet had negative streamwise velocities. Flow visualizations and laser Doppler anemometer measurements showed that this reverse flow is highly turbulent, and suggest that the penetration of a turbulent fluid is larger than that of a laminar or low-turbulence fluid. Finally, the consequences of the instantaneous flow reversals for droplet injection downstream of the perforated plate were analysed, and it was estimated that a small fraction of 10 μm water droplets injected at x/D = 12 could reverse their direction of flight and deposit on the plate.

Numerical and experimental investigation of flow and scour around a half-buried sphere

The paper describes the results of a numerical and experimental investigation of flow and scour around a half-buried sphere exposed to a steady current. Hot-film bed shear stress and Laser Doppler Anemometer measurements were made with a half sphere mounted on the smooth bed in an open channel. The hydrodynamic model is a 3-D general purpose N–S flow solver. The k-omega SST turbulence model was used for closure. The flow model was used to study the horseshoe vortex and lee-wake vortex flow processes around the sphere. The flow model was coupled with a morphologic model to calculate scour around the half-buried sphere in currents. The morphologic model includes a sediment-transport description, and a description of surface-layer sand slides for bed slopes exceeding the angle of repose. The sediment transport description includes, for the first time, the effect of externally-generated turbulence (induced by the horseshoe-vortex flow and the lee-wake flow processes) on sediment transport. The results show that the scour depth increases and time scale decreases when the effect of externally-generated turbulence is incorporated in the calculations. Empirical expressions representing the numerically obtained data on the equilibrium scour depth and the time scale are presented. The results show that the equilibrium maximum scour depth in the live-bed regime can be approximated by 0.5 D in which D is the sphere diameter.

An experimental investigation of air boundary layer flow in grinding using the laser doppler anemometry technique

This paper reports on the motion of the air flow around a rotating grinding wheel based on LDA measurements. The results clearly show the velocity distributions and the turbulence intensity. The experimental results and conclusions give, for the first time, a full understanding of the air boundary layer velocity profiles. Outcomes of this work will help to optimise the design of fluid delivery systems. The grinding wheel rotates at relatively high speed and carries on its surface an air boundary layer flow. This flow may act to divert the grinding fluid stream and prevent it from entering the grinding contact zone resulting in elevated temperatures and reduced grinding efficiency. This has aroused interest and stimulated research in the study of the air boundary layer flow distribution around a rotating grinding wheel. However, a review of prior literature reveals conflicting experimental results obtained from previous investigations due to the use of different experimental measurement methods. Currently, the laser doppler anemometer (LDA) is one of the most effective tools in the measurement of fluid velocity compared with other conventional measurement instruments.

Experimental study and large eddy simulation of turbulent flow around tube bundles composed of wavy and circular cylinders

This paper presents the results of an investigation on the effects of wavy cylindrical tubes in a staggered heat exchanger tube bundle. Experimental measurements and large eddy simulation (LES) technique were used to study the turbulent flow characteristics in a staggered tube bundle arrangement at a sub-critical Reynolds number of Re = 7500. The aim of this investigation is to compare the flow characteristics of a new configuration of cylindrical tubes with that of a similar arrangement which comprises purely circular cylinders. The first row of circular tubes is replaced by a row of wavy cylindrical tubes. The result of the experiment shows that the mean velocity distributions and turbulence intensity, obtained by the present LES method, are in good agreement with the Laser Doppler Anemometer (LDA) measurements. The wake patterns around the second row of cylinders become more well organized upon the introduction of wavy cylinders of optimal wavelength (λ/Dm = 6). The turbulent kinetic energy behind the first row of tubes is also reduced. The power density spectra of the vortex shedding in the tube bundle are evidently suppressed. As a result, the fluctuating forces of the tube bundles are weakened. However, the drag is not noticeably reduced by such modification.

Three-dimensional ray tracing through curvilinear interfaces with application to laser Doppler anemometry in a blood analogue fluid

Prediction of the effects of refractive index (RI) mismatch on laser Doppler anemometer (LDA) measurements within a curvilinear cavity (an artificial ventricle) was achieved by developing a general technique for modelling the paths of the convergent beams of the LDA system using 3D vector geometry. Validated by ray tracing through CAD drawings, the predicted maximum tolerance in RI between the solid model and the working fluid was +/- 0.0005, equivalent to focusing errors commensurate with the geometric and alignment uncertainties associated with the flow model and the LDA arrangement. This technique supports predictions of the effects of refraction within a complex geometry. Where the RI mismatch is unavoidable but known, it is possible not only to calculate the true position of the measuring volume (using the probe location and model geometry), but also to estimate degradation in signal quality arising from differential displacement and refraction of the laser beams.

CFD simulation of bubble columns incorporating population balance modeling

A computational fluid dynamics (CFD)-code has been developed using finite volume method in Eulerian framework for the simulation of axisymmetric steady state flows in bubble columns. The population balance equation for bubble number density has been included in the CFD code. The fixed pivot method of Kumar and Ramkrishna [1996. On the solution of population balance equations by discretization—I. A fixed pivot technique. Chemical Engineering Science 51, 1311–1332] has been used to discretize the population balance equation. The turbulence in the liquid phase has been modeled by a k – ε model. The novel feature of the framework is that it includes the size-specific bubble velocities obtained by assuming mechanical equilibrium for each bubble and hence it is a generalized multi-fluid model. With appropriate closures for the drag and lift forces, it allows for different velocities for bubbles of different sizes and hence the proper spatial distributions of bubbles are predicted. Accordingly the proper distributions of gas hold-up, liquid circulation velocities and turbulence intensities in the column are predicted. A survey of the literature shows that the algebraic manipulations of either bubble coalescence or break-up rate were mainly guided by the need to obtain the equilibrium bubble size distributions in the column. The model of Prince and Blanch [1990. Bubble coalescence and break-up in air-sparged bubble columns. A.I.Ch.E. Journal 36, 1485–1499] is known to overpredict the bubble collision frequencies in bubble columns. It has been modified to incorporate the effect of gas phase dispersion number. The predictions of the model are in good agreement with the experimental data of Bhole et al. [2006. Laser Doppler anemometer measurements in bubble column: effect of sparger. Industrial & Engineering Chemistry Research 45, 9201–9207] obtained using Laser Doppler anemometry. Comparison of simulation results with the experimental measurements of Sanyal et al. [1999. Numerical simulation of gas–liquid dynamics in cylindrical bubble column reactors. Chemical Engineering Science 54, 5071–5083] and Olmos et al. [2001. Numerical simulation of multiphase flow in bubble column reactors: influence of bubble coalescence and breakup. Chemical Engineering Science 56, 6359–6365] also show a good agreement for liquid velocity and gas hold-up profiles.

CFD simulation of bubble column—An analysis of interphase forces and turbulence models

3D transient CFD simulations of bubble column have been performed for a wide range of superficial gas velocity on an industrially relevant cylindrical column and the CFD predictions have been compared with the experiments of Menzel et al. [T. Menzel, T. Weide, O. Staudacher, U. Onken, Reynolds stress model for bubble column reactor, Ind. Eng. Chem. Res. 29 (1990) 988–994]. Simulations have also been performed to understand the sensitivity of different interphase forces (drag, lift, turbulent dispersion and added mass). This work highlights the importance of choosing the CL value and the drag law in accordance with the bubble size. Further, a laboratory scale bubble column with three different spargers (perforated plate, sintered plate and single hole) has been simulated using three different turbulence closure (k–ɛ, RSM and LES) models, with the purpose of critically comparing their predictions with experimental data [M.R. Bhole, S. Roy, J.B. Joshi, Laser doppler anemometer measurements in bubble column: effect of sparger, Ind. Eng. Chem. Res. 45 (26) (2006) 9201–9207; A.A. Kulkarni, K. Ekambara, J.B. Joshi, On the development of flow pattern in a bubble column reactor: experiments and CFD, Chem. Eng. Sci. 62 (2007) 1049–1061]. It has been found that the RSM shows better agreement than the k–ɛ model in predicting the turbulent kinetic energy profiles. Comparatively, the LES has been successful in capturing the averaged behavior of the flow, while at some locations; it slightly over predicts the kinetic energy profiles. Further, it has been able to simulate the instantaneous vortical-spiral flow regime in case of sieve plate column, as well as, the bubble plume dynamics in case of single hole sparger. Thus, LES can be effectively used for study of flow structures and instantaneous flow profiles.