We present a numerical analysis of the convective heat transfer coefficient for the turbulent Taylor–Couette–Poiseuille flow in a concentric annular gap. The study utilizes rotational speeds defined by the Taylor number (Ta) ranging from 2×104 to 1×108, each combined with the axial flow defined by Reynolds number Re=4485, resulting in eight distinct simulation cases in addition to one base case where no rotation is involved. The transient k−ω model available with ANSYS FLUENT for computational fluid dynamics is used for turbulence modelling. The hydrodynamic and thermal fields of the model are validated by comparison with experimental and numerical results from the literature, with an overall qualitatively good agreement. Moreover, the resultant velocity fields exhibit an improvement over the LES results from the literature in comparison with the experimental data. The influence of the flow on the thermal fields is investigated by the swirl parameter N, which compares the rotation speed of the inner cylinder and the mean axial speed. There is no noticeable effect on the thermal fields for the magnitudes of N<1.19. Coherent structures are present for N≥1.19, confirming a direct effect of the temperature and the velocity profiles. The convective heat transfer coefficients (CHTC) are examined by their non dimensional form, the Nusselt number Nu, across the inner rotating wall and the outer static wall. The rotation of the inner wall shows a positive effect on the CHTC for both inner and outer walls. The correlation between the Nu and Ta delivers the exponents of 0.334 and 0.266 for the inner and the outer wall, respectively.

We present an application of a thermal transient model to a coaxial borehole heat exchanger system. We compare two numerical methods. First, a model with a prescribed formation temperature (PFT); secondly, a method with a modeled formation temperature (MFT). In this comparison, several parameters are analyzed, such as the transient temperature profiles, the heat flux along the wellbore, the overall heat transfer rate, the thermal conductivity of the formation, and the type of flow inside the pipe and annulus — laminar or turbulent. The description of the system by the MFT method is more physically consistent. Then we proceed validating this method against two experimental setups, thereby showing good agreement. We perform a sensitivity analysis to the MFT method, varying the direction of the flow, regular and reversed, and the center tube material, with a high (steel) or low (polyethylene) thermal conductivity. It is shown that the reverse circulation has a better heat extraction, while regular flow performs better in the case of heat injection. For the center tube material, polyethylene shows a better thermal performance when compared to steel.

A model for acoustic cavitation flows able to depict large geometries and time scales is proposed. It is based on the Euler-Lagrange approach incorporating a novel Helmholtz solver with a non-linear acoustic attenuation model. The method is able to depict a polydisperse bubble population, which may vary locally. The model is verified and analyzed in a setup with a large sonotrode. Influences of the initial void fraction and the population type are studied. The results show that the velocity is strongly influenced by these parameters. Furthermore, the largest bubbles determine the highest pressure amplitude reached in the domain, which corresponds to the Blake threshold of these bubbles. Additionally, a validation is performed with a small sonotrode. The model reproduces most of the experimentally observed phenomena. In the experiments, neighboring bubbles are found which move in different directions depending on their size. The numerical results show that the responsible mechanism here is the reversal of the primary Bjerknes force at a certain pressure amplitude.

In the design of turbomachinery, the avoidance of flow-induced vibrations offers optimisation potential with regard to noise reduction and the extension of the service life of a machine. To achieve this, damage-relevant should be analyzed in the development phase using methods such as forced response or flutter calculations. A forced response analysis requires the specification of flow-induced excitations in the spectral range, which can be obtained from a temporal numerical simulation using FFT. Since the FFT depends on the time span and therefore only reproduces discrete frequencies, only rotational frequencies and their integer harmonics can be determined from a single rotational period. To work around this, a Dynamic Mode Decomposition (DMD) is applied to analyse the flow field in a high performance centrifugal fan obtained from simulation and measurement data. DMD is a model order reduction method based on singular value decomposition. It extracts modes and eigenvalues of a nonlinear, dynamic system. DMD is considered an ideal combination of proper orthogonal decomposition in space and Fourier transform in time. The numerical data were generated with a CFD calculation based on the unsteady Reynolds-averaged Navier-Stokes equations together with the k-ω SST turbulence model. As a result of this study, it can be shown that the DMD agrees exactly with the analysis of the FFT based on transient local pressure sensors. For the two-dimensional pressure field, however, the DMD deviates significantly from the FFT in the amplitudes for higher-frequency excitations, partly showing better agreement with the measurements of the pressure sensors.

The rising demand for lower noise emissions of car ancillary units due to electrification and higher customer expectations regarding driving comfort results in the need for more silent car components. Hydraulic driven car components in particular are often identified as a major source of noise in the system. Therefore, it is mandatory to investigate the noise sources inside the hydraulic system. In this work, a combined CFD-FEM approach is applied to estimate the flow-induced noise radiation of a mechanically driven transmission pump. To achieve this goal, the mapping procedure to hand over the pressure field from the CFD to the FEM mesh must be valid. For this purpose, the error during the mapping process is evaluated and different parameters, which influence the mapping results, are analyzed. Additionally, the impact of the time step size and the length of the time signal on the frequency resolution of the force signal is investigated to get an appropriate excitation force for the vibroacoustic simulation. Subsequently, a force analysis and a structural FEM simulation are performed to identify which flow phenomenon contributes most to the excitation of the pump housing. Specific locations in the pump with high loads are pointed out. In a final step, the results of the vibroacoustic model are compared to acceleration and sound pressure level measurements of the pump performed in a hemi-anechoic room.

Shifts of frequency and bandwidth of a quartz crystal microbalance (QCM) in contact with a structured, viscoelastic sample have been computed with a linearized version of the lattice Boltzmann method (LBM). The algorithm operates in the frequency domain and covers viscoelasticity. The different domains are characterized by different values of the complex viscosity, η, equivalent to different values of the shear modulus, G. Stiff particles are given large |ηSph|, where |ηSph| must be less than ∼100 ηbulk with ηbulk the viscosity of the ambient liquid. Critical to the computational efficiency is a match of the LBM populations at the upper boundary of the simulation box to an analytical solution of the Stokes equation in the bulk above the box. The application example is a test of the ΔΓ/(-Δf)-extrapolation scheme, where Δf and ΔΓ are the shifts in resonance frequency and half bandwidth, respectively. For adsorbed particles, plots of ΔΓ/(-Δf) versus - Δf/n (with n the overtone order) show almost straight lines. The extrapolation of these lines to zero yields a frequency shift, which, after conversion to a thickness with the Sauerbrey equation, closely agrees with the height of the particles. Plots of Δf/n and ΔΓ/n versus n look similar to the corresponding plots obtained for viscoelastic films, where the parameters, which would usually be extracted from those plots (apparent mass and apparent compliance), depend on the geometry and the sample's viscoelasticity in a nontrivial way.

The efficiency requirements for hydraulic pumps applied in automatic transmissions in future generations of automobiles will increase continuously. In addition, the pumps must be able to cope with multiphase flows to a certain extent. Given this background, a balanced vane pump (BVP), an internal gear pump (IGP) and a three-dimensional geared tumbling multi chamber (TMC) pump are analyzed and compared by a computational fluid dynamics (CFD) approach with ANSYS CFX and TwinMesh. Furthermore, test bench measurements are conducted to obtain experimental data to validate the numerical results. The obtained numerical results show a reasonable agreement with the experimental data. In the first CFD setup, the conveying characteristics of the pumps with pure oil regarding volumetric efficiencies, cavitation onset and pressure ripple are compared. Both the IGP and the BVP show high volumetric efficiencies and low pressure ripples whereas the TMC shows a weaker performance regarding these objectives. In the second CFD setup, an oil-bubbly air multiphase flow with different inlet volume fractions (IGVF) is investigated. It can be shown that free air changes the pumping characteristics significantly by increasing pressure and mass flow ripple and diminishing the volumetric efficiency as well as the required driving torque. The compression ratios of the pumps appear to be an important parameter that determines how the multiphase flow is handled regarding pressure and mass flow ripple. Overall, the BVP and the IGP show both a similar strong performance with and without free air. In the current development state, the TMC pump shows an inferior performance because of its lower compression ratio and therefore needs further optimization.

Low noise emissions of vehicle components are today a quality feature in the automotive sector. In automatic transmissions in particular, the hydraulic pump often contributes significantly to noise, which motivates research to clarify the noise sources and transmission pathways in these components. The subject of the present investigation is the generation of noise by the inherently instationary flow in hydraulic pumps. In order to shed some light on these phenomena, a computational fluid dynamics (CFD) simulation model for flow investigations on rotary vane pumps was set up. In this work, first the influence of different simulation parameters on the numerical results is analyzed. Then the pressure in the internal displacement chambers of the pump is examined, as it can be assumed that this is the essential parameter for noise generation. Different operating conditions such as rotational speeds and delivery pressures are investigated. Furthermore, the simulation results are compared to pressure measurements for validation and are used to find optimization potentials.

A modular simulation approach is used to compute the flow of a fluid and the mass transport of tracers in the void space of computer-generated porous packings. Effective transport properties such as the diffusive tortuosity and the dispersion tensor are determined. First, we present and compare two different approaches to model mass transport in homogeneous porous media. Subsequently, heterogeneous porous media are considered, where we investigate the effect of walls on the structure of confined random sphere packings and how it affects the mass transport properties of a sphere packing. In addition, the hydraulic tortuosity is computed and its performance as a descriptor of porous media is compared with that of the diffusive tortuosity.

Vane pumps are often applied in automatic transmission systems of vehicles. Future applications require the oil pumps to be more efficient and to be able to handle multiphase flow pumping situations to a certain extend. To fulfill these requirements, efficient development tools are needed. Therefore, a less demanding computational 2D model of a fixed-type balanced vane pump was derived and numerically analyzed with the commercial computational fluid dynamics (CFD) software ANSYS CFX. The meshing of the rotating parts was done with TwinMesh, using a moving mesh approach. At first, a mesh convergence study was performed. It was shown that the resolution of the radial clearances in particular had a significant influence on the predicted leakages and the volumetric efficiency. The leakage was further investigated concerning the dependence on rotational speed and delivery pressure. In the next step, multiphase flows were considered. In a first setup, vapor cavitation was analyzed and the influence of the alignment of the suction ports on its onset was derived. In a second setup, the influence of different inlet volume fractions of free air was evaluated. The employed multiphase modeling approach was presented and a sensitivity analysis on modeling parameters was performed. Overall, it was shown that free air in the suction ports changed the pumping characteristic of the vane pump significantly. Pressure and flow ripple increased, and the volumetric efficiency and the mean power demand decreased significantly with an increasing inlet volume fraction.

Mass transport in liquid-filled pores at the micro- and nanoscale can play an important role in applications such as membrane separations, chromatography, and catalytic processes. In this work, we use Brownian dynamics in order to describe the motion of spherical solute molecules at a pore-scale. The method can be used to calculate effective parameters intrinsically related to the porous medium such as the effective diffusivity and the hindrance factor for diffusion. The latter is calculated using a novel probabilistic model derived in the present study, which uses the Lennard-Jones potential to reproduce the hindering effect of the interaction between solute molecules and the wall atoms on the diffusivity. In addition, we introduce a fitting function that can be used to estimate the diffusive hindrance factor of a complex geometry when the pore size distribution of the porous network is known. Finally, a multiscale approach is presented and illustrated with an application example, whereby the hindrance factors of the micro- and nanoscale are used in the simulations of the mass transport at the larger scale.

Predicting the pressure drop in the flow through a particle-filled reactor is of great importance in chemical engineering. When the particles are relatively large compared to the characteristic length of the reactor, the confining walls can have a great influence on the flow and thus on the pressure drop. Thus, the effect of geometry on the pressure drop in packed beds is subject of extensive research since decades. Many experimental findings and derived correlations exist which differ widely. In the present work, a computer-based approach is used to study this effect systematically and to contribute to a clarification of these discrepancies. In contrast to common correlations, the results clearly show, that the pressure drop is a nonmonotonic function of the reactor hydraulic diameter-to-sphere diameter ratio. Furthermore, three different reactor geometries, a pipe, a channel and two infinitely extended plates, are studied in order to investigate the universality of the correlations. The results show that for high ratios of hydraulic diameter of the reactor to sphere diameter the three geometries behave similar, whereas for small ratios the pressure drop is difficult to cast in simple correlations.

Simulation in engineering sciences comprises the analysis of complex technical devices and processes using numerical methods. Simulation is clearly an indispensable tool in industry and research/development with huge potential but also with pitfalls and restrictions. Thus, engineers have to be aware of these aspects which is the reason why this topic was introduced at TU Clausthal as a mandatory course with hands on exercises in 2010. The steadily increasing number of participants revealed several disadvantages of the original concept in that the learning experience was unsatisfactory while the personnel effort increased dramatically. Individualized learning was difficult to realize under these circumstances. Thus, a new teaching and learning concept has been designed and implemented focusing on instructional videos which allow offline teaching and training and which allows to adapt to the individual learning speed. The new concept not only imparts technical and methodological competence, but also system, social and intercultural competence.

A numerical investigation of the effect of sensitive parameters on the controlled electrodeposition of charged nanoparticles driven by an electric field is conducted. By applying a potential difference between an arrangement of electrodes, an electric field is generated, in which charged nanoparticles are transported through a mask and finally deposited on a substrate, a technique first described and applied by Choi a al. Using this technique, sharply delimited structures of deposited particles can be printed. A series of simulations are carried out taking into account the variation of different parameters such as the geometry of the electrode arrangement as well as the size and charge of the particles. The numerical results are verified with experimental and numerical data from Choi a al. It is determined how the considered parameters affect the deposition of the nanoparticles with respect to the sharpness of the obtained deposits. Here, the investigated spherical particles showed an inertia-free behavior within the considered diameters from 5 to 30 nm. The correlation of the thermal fluctuations with the electric force is quantitatively analyzed, as well as its impact on the width of the pattern of deposited nanoparticles.

Acoustic cavitation typically forms a variety of bubble structures of generally unknown and broad size distributions. As the bubbles strongly oscillate, their (equilibrium) sizes are not directly observable. Here, a method is presented to experimentally determine the size distribution in bubble populations from high-speed imaging of the bubbles in oscillation. To this end, a spherical bubble model is applied in statistical fashion. This technique is applied to several experimentally realized bubble structures: streamer filaments, clusters, and a peculiar structure we report here on, the acoustically cavitated jet. It is generated by the sonication of a submerged jet to produce abundant cavitation at low flow velocities. Our analysis is complemented by numerical exploration of the hydrodynamic and acoustic properties of the experimental configuration in which the observed bubble structures are formed.

SimScience 2017 workshop proceedings on simulation and optimization in networks, simulation of materials, sistributed simulations, simulation and optimization in networks, multiscale systems, public & transportation network, distributed architectures, parallel architectures.

Many simulations require large amounts of computing power to be executed. Traditionally, the computing power is provided by large high performance computing clusters that are solely built for this purpose. However, modern data centers do not only provide access to these high performance computing systems, but also offer other types of computing resources e.g., cloud systems, grid systems, or access to specialized computing resources, such as clusters equipped with accelerator hardware. Hence, the researcher is confronted with the choice of picking a suitable computing resource type for his simulation and acquiring the knowledge on how to access and manage his simulation on the resource type of choice. This is a time consuming and cumbersome process and could greatly benefit from supportive tooling. In this paper, we introduce a framework that allows to describe the simulation application in a resource-independent manner. It furthermore helps to select a suitable resource type according to the requirements of the simulation application and to automatically provision the required computing resources. We demonstrate the feasibility of the approach by providing a case study from the area of fluid mechanics.

The application of ultrasonic cavitation in chemical processing is a widespread method to accelerate dissolution processes. In recycling technology, often bulk material is introduced into a reactor forming a packed bed of granular particles. Thereby, the cavitation activity at the material surfaces is of interest. In this numerical study, the packed bed is simplified by sphere packings of different arrangement and porosity. The ultrasound propagation model considers the effect of cavitation bubbles by a linearized damping ansatz. A strong sound scattering by the spheres is found for packings with low porosities, while the sphere arrangement is less important.

Liquid-filled pores of Fischer-Tropsch catalyst lead to slow diffusion of the reactants and can cause internal transport limitations leading to a significant decrease of selectivity and productivity. As an approach to overcome these limitations, transport pores can be added to provide an additional pathway for mass transport. In this work, a 3D isothermal model was developed, which takes the effect of concentration gradients within the transport pores into account. A comparison with a 1D model showed, that a description by a 3D model is necessary for transport pores with diameters larger than 10 mu m.