Dr.-Ing. Daniel Klembt

DOI: 10.1016/j.apor.2024.103946

Abstract:

Unexploded Ordnance (UXO) and Discarded Military Munitions (DMMs) are found in many coastal regions. These objects are constantly exposed to environmental influences such as saltwater, which causes corrosion, and waves and currents as well as mobile seabed sediments. The basic assumption to decide if an object is mobilised by waves and currents or not is to compute the critical loads that are needed to move it from its stable position on the sediment bed. The loads on the object are induced by hydrodynamic and hydrostatic forces as well as by friction, gravitation, and inertia. In this study, the hydrodynamic forces were calculated by analytical approaches and numerical simulations (CFD). These forces have been validated for the current-induced mobilisation by wind tunnel experiments. Finally, the dependency of the dimensionless coefficients for lift, drag and added mass of the Reynolds number and the burial depth is transferred into a resulting equation.

DOI: 10.1016/j.applthermaleng.2021.117552

Abstract:

This experimental research was performed for the measurement-based detection and numerical simulation of a biological multiphase flow in a fermentation tank. The difficulties of an investigation are the many complex interactions between the different three phases (yeast as solid, carbon dioxide as gas, wort as liquid). One of the main difficulties is, that the natural convection processes are superimposed by rising gas bubbles in a high turbid fluid. Due to the various problems in optical measurement (e.g. PIV, LDA) the measurement is realised with acoustic sensors, so-called transducers. For a detailed understanding of the results of the acoustic measurement and the associated interpretation of the heat and mass transfer, high demands are on the acoustic measurement technology and the subsequent evaluation due to the real multiphase flow. These requirements are further complicated by the combination of several transducers and the targeted conversion of the measurement technology from a 1D acoustic measurement method to a 2D flow field measurement system. Furthermore, it is shown how problems of the acoustic measurement technology, caused by the multiphase flow, can be solved. The systematic investigation and improvement of the measurement technique allows the direct correlation of the measured temperature fields with the flow fields of the acoustic measurement technique. This combination of temperature and velocity allows the heat transfer of the yeast from the inside to the liquid and the cooling from the outside to the liquid to be analysed and investigated in detail. Finally, the influence of the different phases (yeast as solid, carbon dioxide as gas, wort as liquid) is evaluated, visualised and the complex interactions of the phases on heat and mass transfer are explained. In addition to acoustic measurements in the fermentation fluid, numerical simulations are used to provide additional insights into the processes in a fermenter.

DOI: 10.30464/jmee.2019.3.3.259

Abstract:

In the context of the investigations of multiphase flows, e.g. in cooperation with the local brewery, the convective transport phenomena during the fermentation are investigated. Due to the strong turbidity of the medium, the measurement of velocity profiles is complicated. The difficulties of an investigation with a biological fermentation fluid are the many complex interactions between the different three phases (solid, gas, fluid). Furthermore, natural convection processes are superimposed by rising gas bubbles and the high turbidity of the fluid only allow an acoustic velocity measurement. In previous investigation, ultrasonic transducers are used for the non-contact determination of velocity fields in fluids. The results of these past projects show that the measurement signals of the ultrasonic transducers used can be influenced by many factors. In order to verify the results of the transducers and to investigate the existing uncertainties, a flow configuration with a relatively stable reproducible flow pattern is required. In this study, a calibration system for ultrasonic transducers is developed, manufactured and validated by means of optical measurement technology such as the LDA. Finally, a measurement using Ultrasonic Doppler Velocimetry in a model fluid will be compared with an optical measurement technique.

DOI: 10.30464/jmee.2019.3.3.235

Abstract:

In the context of investigations of real multiphase flows, the university has its own 350 litre fermentation tank with comprehensive acoustic flow and temperature measurement technology for the systematically investigation, of the influence of the fermentation activity, distribution of yeast and occurring convection phenomena. Due to the many problems with the optical (e.g. PIV) and acoustic (e.g. UDV) measurement in a real fermenting fluid the numerical simulation was already used in earlier publications. To validate the numerical models, extensive experimental investigations were carried out which show that the flow in the fermenter is caused only by the reaction products of the yeast and the cooling panels and controls the yeast distribution. In this paper, both the numerical (CFD) and the experimental investigations serve as a starting point to influence the yeast distribution. The described convection flow can only temporarily guarantee the uniform distribution of the yeast in the fermenter until the sedimentation of the yeast at the tank bottom (bottom-fermenting yeast) finally begins. 

DOI: 10.1002/pamm.201800258

Abstract:

In the context of investigations of multiphase flows, the beer production is currently being investigated, especially fermentation, maturation and storage in cooperation with the local brewery. The university has its own 350 litre fermentation tank with comprehensive acoustic flow and temperature measurement technology for the systematical investigation of the influence of the fermentation activity, distribution of yeast and occurring convection phenomena. This paper deals with the numerical simulation of the fermentation tank and the combination of a numerical approach and an experimental investigation with the two Fluid Eulerian‐Eulerian time‐averaged model [3]. The Eulerian‐Eulerian model allows two sets of governing equations, continuity and momentum equations to be solved for either phase and their interactions are modelled using interface transfer terms for interfacial heat, mass and momentum exchanges. As a result, the numerical solution of a natural convection flow which is superimposed by rising gas bubbles will be presented.

DOI: 10.1002/pamm.201900116

Abstract:

In recent years, in addition to the experimental investigation of a flow phenomena, numerical investigation has become increasingly established. Especially in investigations where conventional flow measurement techniques such as PIV or LDA fail, numerical computation can offer new possibilities. Models for the simulation of the natural convection flow in a fermentation tank and in second step a superposition of the natural convection by gas bubbles have already been presented in earlier publications. Based on these results, this paper examines the simulation of yeast using the Euler‐Lagrange model. The aim is to extend the existing simulation, which is based on the Eulerian‐Eulerian time‐averaged model and to validate it with measurements from real experiments with the Ultrasonic Doppler Velocimetry (UDV). Starting point is the Dense Discrete Phase Model (DDPM), which is based on the Kinetic Theory of Granular Flow (KTGF). Especially the physical interaction models, for example the lift force, virtual mass force and collision models, play an important role. These fundamental studies must be conducted because the behaviour of the real yeast is really complex. During real fermentation, the yeast increases over time and also combines with other yeast particles. As a result, the proportion of yeast in the process increases and the equivalent particle size also increases due to the combination of the yeast. The goal of this paper is a numerical simulation of the flow processes in the fermentation tank, based on the Eulerian‐Eulerian model with the additional DDPM as realistic as possible, taking into account the natural convection flow and the actual bubble behaviour as well as the yeast distribution.

DOI: 10.7795/810.20190809

Abstract:

In this investigation, the influence between different bottom shapes of fermentation tanks and the different resulting velocity and temperature fields at the beer production are investigated. The difficulties of an investigation with a biological fermentation fluid (wort) are the many complex interactions between the different three phases (yeast, carbon dioxide bubbles, wort). Furthermore, natural convection processes are superimposed by rising gas bubbles and the high turbidity of the fluid only allows acoustic or magnetic resonance tomography velocity measurements. This leads to high requirements for the measurement technology and the following evaluation. In this study, latest measurements with two coupled UDV-Systems for a high-resolution velocity field combined with a data acquisition unit for the temperature field in the fermentation tank with two bottom shapes (conical, hemispherical) are presented. The new experimental setup consists of a velocity field of 16 x 2 MHz and 19 x 4 MHz transducers, 56 temperature sensors and enables an improved resolution compared to the previous measurements. For a precise evaluation, the filtering of interferences is carried out by an additional, self-written program. Finally, the experimental analysis of the flow and temperature measurements and the transport mechanism (momentum and heat) with a real fermentation fluid, in different bottom shapes, are presented.