Jochen Fröhlich

TU Dresden | TUD · Institut für Strömungsmechanik

The paper presents Large Eddy Simulations of plane channel o w at a friction Reynolds number of 180 and 395 with a block-structured Finite Volume method. Local grid renemen t near the solid wall is em- ployed in order to reduce the computational cost of such simulations or other simulations of wall-bounded o ws. Dieren t subgrid-scale models are em...

High-resolution large-eddy simulation is used to investigate the mean and turbulence properties of a separated flow in a channel constricted by periodically distributed hill-shaped protrusions on one wall that obstruct the channel by 33% of its height and are arranged 9 hill heights apart. The geometry is a modification of an experimental configura...

The coupling of large eddy simulation (LES) with statistical turbulence models, i.e. Reynolds-Averaged Navier–Stokes (RANS) models, is arguably the main strategy to drastically reduce computational cost for making LES affordable in a wide range of complex industrial applications. The present paper presents a coherent review of the various approache...

The paper reports on three direct numerical simulations of sediment transport with different prototypical non-spherical particle shapes, ranging from prolate to oblate to a triaxial ellipsoidal shape, and a fourth simulation with spherical particles. All physical and numerical parameters of these simulations are identical, including bulk Reynolds n...

The paper addresses the fluid–structure interaction of submerged aquatic canopies, with particular focus on the complex interplay between coherent flow structures and the motion of vegetation elements. New insights into the underlying mechanisms are gained from a large eddy simulation of a submerged model canopy flow. The model canopy is made up of...

Der Beitrag zieht eine erste Bilanz des Lernprojekts Shanvi (Strömungen hautnah, nicht virtuell). Es wurde konzipiert, um Studierenden eigenständige Erfahrungsmöglichkeiten in der Strömungsmechanik zu bieten, die über den normalen Universitätsbetrieb hinausgehen. Neben der direkten Erfahrung zu physikalischen Phänomenen und der eigenverantwortliche...

As an advanced oxidation process, hydrodynamic cavitation generates radicals inducing reduction of chemicals in water. In the present work dye degradation is investigated as a representative for such chemical. Cavitation intensity, outgassing and flow reactivity largely depend on pressure boundary conditions. The paper presents an experimental stud...

A novel Y-shaped membraneless flow-through electrolyzer is introduced to achieve a homogeneous electrochemical reaction across the entire electrode in a cost-efficient cell design with effective product separation. Numerical simulations of the electrolyte flow and electrical current within the already known I-and T-shaped cells motivate the newly p...

Bubble deformation and breakup due to strain-rate-induced stress is investigated for a laminar flow configuration. The bubble shape is assumed to be a prolate ellipsoid. A new model for bubble deformation under dynamic load is introduced in the form of an ordinary differential equation for the deformation energy. Breakup is identified with a critic...

Knowledge of the cleaning mechanism is necessary to choose a suitable model for a cleaning simulation. In the present work, an existing classification scheme for cleaning mechanisms is considered. Altough this framework is quite promising, the generation of training data constitutes a bottleneck, since the labeling was done manually and very roughl...

In this contribution the authors investigate how flushing of chocolate using a follow‐up chocolate in a straight horizontal pipe is affected by temperature. The authors investigate a non‐uniform distribution of temperature across the considered domain. This is done using two cases, where the first exhibits a wall temperature deviating from the norm...

Modelling flotation fundamentals is segregated into hydrodynamics, surface hemistry, and froth. At present, a widely accepted understanding of how these processes are linked to each other and a comprehensive set of experimental data that can be used as a flotation modelling reference is missing. A binary particle system was used to perform an exte...

In the present contribution, a numerical simulation of the flow over idealized aquatic canopy patches is presented. These patches consist of flexible blades interacting with the surrounding flow. The physical parameters governing the flow, the characteristics of the blades and their positioning within the vegetation patches are identical to a previ...

Rotor internal cooling is a new concept for high power density electric vehicle drives. A turbulent pipe flow is injected into a cylindrical cavity in the rotor shaft of the motor. The flow is deflected in the cavity, accelerated in circumferential direction by the rotor wall and exits through an annular duct with the outer wall rotating. Due to th...

The paper is concerned with fast and robust contact detection methods for arbitrary ellipsoids. An iterative procedure, namely the Levenberg‐Marquardt method, based on the common normal concept for parametric ellipsoids, is employed together with an implementation of the widely used GJK algorithm for comparison. The performance and accuracy of both...

This paper presents a numerical method to study the collision process of mineral particles and air bubbles in flotation cells. A bubble‐resolved and particle‐modelled direct numerical simulation was performed to study the particle–bubble collision frequency for representative flotation conditions. The location of the particle collisions on the bubb...

This work aims to improve the turbulence modeling in RANS simulations for particle-laden flows. Using DNS data as reference, the errors of the model assumptions for the Reynolds stress tensor and turbulence transport equations are extracted and serve as target data for a machine learning process called SpaRTA (Sparse Regression of Turbulent Stress...

The intermediate wake of a circular cylinder at Reynolds number 3300 is studied by means of highly resolved large eddy simulations. The domain spans 100 cylinder diameters D downstream of the cylinder. The intermediate wake is taken here as the region between 6D and 50D downstream of the cylinder. Initially , the velocity deficit shows a marked dec...

Predicting the cleaning time required to remove a thin layer of soil is a challenging task and subject of current research. One approach to tackle this problem is the decomposition into physical sub-problems which are modelled separately and the subsequent synthesis of these models. In this paper, an existing model for adhesive detachment is extend...

Turbines are core components in jet engines for flight propulsion, power plants, and other important energy conversion processes. They are composed of successive rows of blades so that wakes of upstream blades reach subsequent blades where they perturb the flow in an unsteady manner. At the point where a wake reaches the downstream blades, the pert...

The present study investigates the transport of dilute bubbles by transitional flow in a joining, cross-flow-type T-junction channel geometry with Reynolds numbers at the outlet branch from Re3 = 600 to 1800 and an inlet volume flow rate ratio of 1. Bubbles with diameters between db = 400 and 600 µm are considered. The schematic pattern of the sing...

The paper analyzes the migration of non-spherical particles in curved micro-channels. Inertial migration combined with Dean drag results in a reduced set of stable focusing positions in specific regions of the cross section of the channel. These are studied using fully resolved transient simulations of particulate flows in rectangular curved ducts...

The paper reports on simulations of particulate flows in square ducts with oblate and prolate particles at a bulk Reynolds number of 100 and dilute particle concentration. Inertial migration leads to focusing of particles in specific regions of the cross section. It is observed that these positions are different for the non-spherical particles comp...

To clean highly viscous fluids from pipework, flushing processes are used. The cleaning time for a pair of fluids, one being flushed and one used for flushing the other out, is typically estimated by using expensive experiments or costly fully resolved numerical simulations. In this work the authors propose a new approach to determine an accurate a...

An open-box machine learning algorithm (sparse symbolic regression) is used to generate improved turbulence models for sediment transport from DNS data. For that purpose, the SpaRTA (Sparse Regression of Turbulent Anisotropy) of Schmelzer et al. is extended to flows with sediment transport and a new dissipation analogy for constructing correction t...

Particle-laden ows occur in many ways in natural and technological situations. Jain et al. [1] presented four DNS studies of sediment transport with di erent particle shapes. The one conducted with spherical particles was used in the present work to apply a machine learning (ML) algorithm to improve the turbulence modelling in RANS simulations. Ch...

Cleaning is an important process step in the food industry, especially to avoid contamination during increasingly frequent product changes. The equipment is cleaned almost daily causing high ecological and economic expenses. Predicting the cleaning time required to remove a thin soil layer for given operating conditions can prevent the use of unnee...

Abstract: A set of closure models for the Euler-Euler two-fluid framework that was previously established for bubbly flows, in a variety of different geometries comprising pipes, columns and stirred tanks by Rzehak et al. 2017 and Shi et al. 2018, is applied here to a turbulent bubbly jet. The closure models for momentum exchange comprise drag-, li...

The article describes direct numerical simulations using an Euler–Lagrange approach with an immersed-boundary method to resolve the geometry and trajectory of particles moving in a flow. The presentation focuses on own work of the authors and discusses elements of physical and numerical modeling in some detail, together with three areas of applicat...

Cleaning is an important process step in the food industry, especially to avoid contamination during increasingly frequent product changes. The equipment is cleaned almost daily causing high ecological and economic expenses. Predicting the cleaning time required to remove a thin soil layer can prevent the use of unneeded resources. The authors rece...

In turbomachines, rotors and stators differ by the rotation of the former. Hence, half of each stage is directly influenced by rotation effects. The influence of rotation on the flow structure and its impact on the performance is studied through Wall-Resolving Large Eddy Simulations of a rotor with large relative tip gap size. The simulations are p...

The article proposes an algorithm to model the collision between arbitrary ellipsoids in viscous fluid. It is composed of several steps, each improving upon the standard procedure employed in the current literature. First, an efficient contact detection algorithm is presented. Then, the semi-implicit Immersed Boundary Method of Tschisgale et al. (2...

The paper addresses a fluid-structure problem involving a trapezoidal ribbon which undergoes large static reconfiguration, yielding a drag force independent of the velocity over a sizable velocity range. With experimental reference data on shape and drag available in the literature, the paper reports on Large Eddy Simulations of the configuration p...

Data from direct numerical simulations of disperse bubbly flows in a vertical channel are used to study the effect of the bubbles on the carrier-phase turbulence. We developed a new method, based on an extension of the barycentric map approach, that allows us to quantify and visualize the anisotropy and componentiality of the flow at any scale. Usi...

There has been considerable discussion in recent years concerning whether a log-law exists for wall-bounded, turbulent bubbly flows. Previous studies have argued for the existence of such a log-law, with a modified von Kármán constant, and this is used in various modelling studies. We provide a critique of this idea, and present several theoretical...

The removal of film-like deposits is a challenge in many fields of production. For environmental and economic reasons, the cleaning processes need to be optimized. An optimization by means of computational fluid dynamics seems to be beneficial, but is subject to some restrictions, especially in industrial context. General modeling ideas, a subdivis...

Impinging circular free-surface water jets are used in challenging cooling and cleaning tasks. In order to develop simulation models for process optimization, validation data are required, which are currently not available. Therefore, the flow field of these jets is studied for the first time with the novel laser Doppler velocity profile sensor. Th...

The removal of film-like soils is a challenge in many fields of production for consumer goods. For ecological and economic reasons, these cleaning processes have to be optimized. A model for the prediction of the cleaning times of adhesively detaching soils is presented. It is formulated as a boundary condition for CFD simulations, which reduces th...

Vortragsseminare finden klassischerweise in Präsenz statt. Der coronabedingte Lockdown im Sommersemester 2020 zwang alle Lehrveranstaltungen in den virtuellen Raum. Dieser Beitrag stellt die in drei verschiedenen Vortragsseminaren an der Fakultät Maschinenwesen der TU Dresden implementierten Anpassungen zur Durchführung unter Kontaktbeschränkungen...

Dispersed multiphase flow can be simulated by the Euler-Lagrange approach where the continuous phase is described on the Euler grid and the dispersed phase is treated as Lagrange points. The point-mass Euler-Lagrange method requires the bubble or particle size to be much smaller than the cell size when the interphase coupling is considered. Otherwi...

In turbomachines, rotors and stators differ by the rotation of the former. Hence, half of each stage is directly influenced by rotation effects. The influence of rotation on the flow structure and its impact on the performance is studied through Wall-Resolving Large Eddy Simulations of a rotor with large relative tip gap size. The simulations are p...

This study of a cavitating jet in a reactor with different nozzle diameters and pressure differences is focused on evaluating a cavitation flow in terms of process engineering use, for process optimization and for reproducibility of the experiment. For this purpose, optical images of the flow were acquired, significant process variables were measur...

This article provides a summarizing account of the results obtained in the current collaborative work of four research institutes concerning near-wall flow in turbomachinery. Specific questions regarding the influences of boundary layer development on blades and endwalls as well as loss mechanisms due to secondary flow are investigated. These addre...

Thermal-hydraulic conditions in a partially uncovered nuclear fuel assembly mock-up are studied with particular focus on the influence of the horizontal air flow above the rod bundle. The investigations are performed at the ALADIN test facility, which models a boiling water reactor fuel assembly at a 1:1 scale both axially and radially. In the scen...

Data from Direct Numerical Simulations of disperse bubbly flows in a vertical channel are used to study the effect of the bubbles on the carrier-phase turbulence. A new method is developed, based on the barycentric map approach, that allows to quantify the anisotropy and componentiality of the flow at any scale. Using this the bubbles are found to...

A statistical learning approach is presented to predict the dependency of steady hydrodynamic interactions of thin oblate spheroidal particles on particle orientation and Reynolds number. The conventional empirical correlations that approximate such dependencies are replaced by a neural-network-based correlation which can provide accurate predictio...

For elliptic equations in three dimensions, the runtime of discontinuous Galerkin methods typically scales with O(p^4 n_e) , where p is the polynomial degree and n_e the number of elements and structure exploitation via tensor-product bases is assumed. For local discontinuous Galerkin methods that allow for hybridization, the authors were able to l...

This paper treats the separation of particles in microchannels relevant to biological and industrial process engineering. To elucidate the mechanisms creating uneven distribution of particles over the cross section, simulations are conducted with the particles being geometrically resolved and coupled to the fluid by an immersed-boundary method. In...

Linear cascades are commonly used as surrogate geometries when performing fundamental studies of turbomachinery blading. Several effects are not accounted for in linear cascades, among them the relative motion between blade and endwall. In this study three different relative endwall velocities are analysed. The effect of the relative motion between...

Linear cascades are commonly used as surrogate geometries when performing fundamental studies of turbomachinery blading. Several effects are not accounted for in linear cascades, among them the relative motion between blade and endwall. In this study three different relative endwall velocities are analysed. The effect of the relative motion between...

In this work, an efficient model for simulating bubble dispersion and coalescence due to turbulence is developed in the Euler-Lagrange framework. The primary liquid phase is solved on the Euler grid with the RANS turbulence model. Bubble motion is computed with the force balance equations. One-way coupling between two phases is assumed and the fram...

This paper presents a numerical method for the simulation of fluid-structure interaction specifically tailored to interactions between Newtonian fluids and a large number of slender viscoelastic Cosserat rods. Because of their high flexibility and low weight the rods considered here exhibit large deflections, even under moderate fluid loads. Their...

This paper presents a numerical method for the simulation of fluid-structure interaction specifically tailored to interactions between Newtonian fluids and a large number of slender viscoelastic Cosserat rods. Because of their high flexibility and low weight the rods considered here exhibit large deflections, even under moderate fluid loads. Their...

This paper proposes a matrix-free residual evaluation technique for the hybridizable discontinuous Galerkin method requiring a number of operations scaling only linearly with the number of degrees of freedom. The method results from application of tensor-product bases on cuboidal Cartesian elements, a specific choice for the penalty parameter, and...

The original manuscript contains scribal errors in the main equation. This corrigendum contains the correct equations. Results and conclusions in the original manuscript are not affected.

Removing inclusions from the melt is an important task in metallurgy with critical impact on the quality of the final alloy. Processes employed with this purpose, such as flotation, crucially depend on the particle size. For small inclusions, the aggregation kinetics constitute the bottleneck and, hence, determine the efficiency of the entire proce...

Data from direct numerical simulations (DNS) of disperse bubbly flow in an upward vertical channel are used to develop a new second-moment closure for bubble-induced turbulence (BIT) in the Euler-Euler framework. The closure is an extension of a BIT model originally proposed by Ma et al. (Phys. Rev. Fluids, vol. 2, 2017, 034301) for two-equation ed...

The cleaning behaviour of a pre-wetted soil is studied experimentally and modelled numerically for the prototypical case of plane channel flow. One of the channel walls is soiled with a food-based model soil containing luminescent tracer particles to perform space- and time-resolved investigations of the cleaning process. Pre-wetting is applied for...

The paper presents four direct numerical simulations of an open channel flow with geometrically resolved particles heavier than the fluid. In each simulation the same number of mono-disperse particles is considered, with the shape of the particles varied between the simulations, while conserving the volume. Three simulations are reported with non-s...

The equations for double-mean, form-induced and spatially averaged turbulent energy budgets are employed to analyse data from direct numericalsimulations of turbulent open-channel flows over transitionally rough mobile beds with intermediate flow submergence. Two scenarios were con-sidered related to (i) near-critical bed condition, and (ii) fully...

High-order methods gain more and more attention in computational fluid dynamics. Among these, spectral element methods and discontinuous Galerkin methods introduce element-wise approximations by means of a polynomial basis. This leads to a small number of operators consuming a large portion of the runtime of CFD applications. The present paper addr...

Turbines are essential components of jet planes and power plants. Therefore, their efficiency and service life are of central engineering interest. In the case of jet planes or thermal power plants, the heating of the turbines due to the hot gas flow is critical. Besides effective cooling, it is a major goal of engineers to minimize heat transfer b...

High-order methods gain increased attention in computational fluid dynamics. However, due to the time step restrictions arising from the semi-implicit time stepping for the incompressible case, the potential advantage of these methods depends critically on efficient elliptic solvers. Due to the operation counts of operators scaling with the polynom...

The article proposes an algorithm to model the collision between arbitrary ellipsoids in viscous fluid. It is composed of several steps, each improving upon the standard procedure employed in the current literature. First, an efficient contact detection algorithm is presented. Then, the semi-implicit Immersed Boundary Method of Tschisgale et al., 2...

Turbines are essential components of jet planes and power plants. Therefore, their efficiency and service life are of central engineering interest. In the case of jet planes or thermal power plants, the heating of the turbines due to the hot gas flow is critical. Besides effective cooling, it is a major goal of engineers to minimize heat transfer b...

The removal of film-like deposits is a challenge in many fields of production. For environmental and economic reasons, the cleaning processes need to be optimised. An optimisation by means of computational fluid dynamics seems to be beneficial, but is subject to some restrictions, especially in industrial context. General modelling ideas, a subdivi...

Splat and antisplat events are a widely found phenomenon in three-dimensional turbulent flow fields. Splats are observed when fluid locally impinges on an impermeable surface transferring energy from the normal component to the tangential velocity components, while antisplats relate to the inverted situation. These events affect a variety of flow p...

The baseline model for the CFD-simulation of turbulent bubbly flows in the Euler-Euler framework was proposed several years ago. It defines a fixed set of closures including all constants to avoid case by case tuning and to have a basis for sustainable model development. The present paper extends the baseline model by improving the modelling of bub...

The present paper provides a collision model for Cosserat rods, able to represent a very general collision response, including frictional effects as well as multiple simultaneous collisions of a large number of rods. The proposed collision model falls into the category of constraint-based collision models. This concept is extended to a general clas...

The paper studies the response of a cluster of bubbles to osmotic pressure, and steady and oscillatory shearing by detailed numerical simulations. In contrast to other investigations, the movement of the interstitial fluid is fully resolved. To that end, an immersed-boundary method is employed, yielding the trajectory of each bubble and the flow an...