Stochastic modeling and large-eddy simulation of heated concentric coaxial pipe flow

Turbulent concentric coaxial pipe flows are numerically investigated as canonical problem addressing spanwise curvature effects on heat and momentum transfer that are encountered in various engineering applications. It is demonstrated that the wall-adapting local eddy-viscosity (WALE) model within a large-eddy simulation (LES) framework, without model parameter recalibration, has limited predictive capabilities as signalized by poor representation of wall curvature effects and notable grid dependence. The identified lack in the modeling of radial transport processes is therefore addressed here by utilizing a stochastic one-dimensional turbulence (ODT) model. A standalone ODT formulation for cylindrical geometry is used in order to asses to which extent the predictability can be expected to improve by utilizing an advanced wall-modeling modeling strategy. It is shown that ODT is capable of capturing spanwise curvature and finite Reynolds number effects for fixed adjustable ODT model parameters. Based on the analogy of heat and mass transfer, present results yield new opportunities for modeling turbulent transfer process in chemical, process, and thermal engineering.Comment: In: New Results in Numerical and Experimental Fluid Mechanics XIV -- Contributions to the 23rd STAB/DGLR Symposium Berlin, Germany, 2022, edited by Andreas Dillmann, Gerd Heller, Ewald Kr\"amer, Claus Wagner, and Julien Weis

Stochastic Modeling of Electrohydrodynamically Enhanced Drag in One-Way and Fully Coupled Turbulent Poiseuille and Couette Flow

Die gemeinsame Modellierung von hydrodynamischen und elektrokinetischen Prozessen stellt eine numerische Hürde dar, die jedoch für verschiedene Anwendungen in der Elektrochemie oder im Energieingenieurwesen kritisch ist. Der aktuelle Modellierungsbedarf für elektrohydrodynamische (EHD), turbulente Strömungen liegt in den kleinskaligen Prozessen und Skalenwechselwirkungen. Um diese Einschränkungen zu überwinden, wird ein stochastisches, eindimensionales Turbulenzmodell (ODT) genutzt. Das Modell zielt darauf ab, alle relevanten Skalen der Strömung aufzulösen, jedoch nur entlang einer gedachten Linie. Turbulente Advektion wird durch eine stochastisch gezogene Sequenz an Wirbelereignissen, welche deterministische molekular-diffusive Prozesse unterbrechen, modelliert. In dieser Studie werden zwei kanonische Strömungskonfigurationen untersucht, die verschiedene Kopplungsstrategien und physikalische Prozesse adressieren. Zuerst werden EHD-Effekte in der vertikalen Rohrströmungen eines idealen Gases variabler Dichte und einer konzentrischen, axialen Elektrode mit einem einfach gekoppelten Modellformulierung untersucht. Elektrische Felder werden durch eine Corona-Entladung und eine als konstant angenommene elektrische Ladungsverteilung vorgeschrieben. Danach werden EHD-Effekte in der turbulenten Grenzschicht mithilfe der etwas einfacher aufgebauten ebenen Couette-Strömung einer univalenten, ionischen Flüssigkeit unter Nutzung der vollständig gekoppelten Modellformulierung untersucht. Beide Anwendungsfälle demonstrieren, dass das ODT-Modell Vorhersagefähigkeit besitzt, da mehrskalige Transportprozesse aufgelöst werden können. Die gewonnen Ergebnisse legen nahe, dass das teurere vollständig gekoppelte Verfahren, im Gegensatz zum günstigeren einfach gekoppelten Verfahren, verwendet werden sollte, wenn die Relaxationszeiten der Ladungsträger signifikant größer als die mittlere advektive Zeitskala der Strömung ist.Joint predictive modeling of hydrodynamics and electrokinetics is a standing numerical challenge but crucial for various applications in electrochemistry and power engineering. The present lack in modeling of electrohydrodynamic (EHD) turbulent flows lies in the treatment of small-scale processes and scale interactions. To overcome these limitations, a stochastic one-dimensional turbulence (ODT) model is utilized. The model aims to resolve all scales of the flow, but only on a notional line-of-sight, modeling turbulent advection by a stochastically sampled sequence of eddy events that punctuate deterministic molecular diffusive advancement. In this study, two canonical flow configurations are investigated that address different coupling strategies and flow physics. First, EHD effects in a variable-density vertical pipe flow of an ideal gas with an inner concentric electrode are investigated with a one-way coupled model formulation. Electric fields are generated by means of a corona discharge and the corresponding effect of a fixed ionic charge density field. Second, in order to reduce physical complexity, EHD effects the turbulent boundary layers in plane Couette flow of an isothermal univalent ionic liquid are investigated with a fully coupled model formulation. Both application cases demonstrate that ODT has predictive capabilities due to multiscale resolution of transport processes. Present results suggest that more expensive fully than one-way coupling of electrokinetics is crucial when charge relaxation times are significantly larger than the mean advection time scale

Empowering the Configuration-IP - New PTAS Results for Scheduling with Setups Times

Integer linear programs of configurations, or configuration IPs, are a classical tool in the design of algorithms for scheduling and packing problems, where a set of items has to be placed in multiple target locations. Herein a configuration describes a possible placement on one of the target locations, and the IP is used to chose suitable configurations covering the items. We give an augmented IP formulation, which we call the module configuration IP. It can be described within the framework of n-fold integer programming and therefore be solved efficiently. As an application, we consider scheduling problems with setup times, in which a set of jobs has to be scheduled on a set of identical machines, with the objective of minimizing the makespan. For instance, we investigate the case that jobs can be split and scheduled on multiple machines. However, before a part of a job can be processed an uninterrupted setup depending on the job has to be paid. For both of the variants that jobs can be executed in parallel or not, we obtain an efficient polynomial time approximation scheme (EPTAS) of running time f(1/epsilon) x poly(|I|) with a single exponential term in f for the first and a double exponential one for the second case. Previously, only constant factor approximations of 5/3 and 4/3 + epsilon respectively were known. Furthermore, we present an EPTAS for a problem where classes of (non-splittable) jobs are given, and a setup has to be paid for each class of jobs being executed on one machine

The One-Dimensional Turbulence Aspects of Internal Forced Convective Flows

We present an overview of issues for the modeling of internal forced convective flows with the One-Dimensional Turbulence (ODT) model. Results of recent research as well as prospective research issues are presented for statistically streamwise homogeneous flows and streamwise inhomogeneous mixed convective flows. The results illustrate the capabilities of the model to evaluate and bring insight into a wide range of physical phenomena in the field of convective flows. Nonetheless, as a model, ODT is best suited for the evaluation of asymptotically turbulent flows, i.e., away from laminar regimes

EHD Turbulence in Channel Flows with Inhomogeneous Electrical Fields: A One-Dimensional Turbulence Study

Electricly enhanced flows can be found in various technical applications as, for example, in air cleaning devices and liquid metal or redox flow batteries. For both examples mentioned it is crucial to develop a general understanding of the relevant physical processes and model them economically. Additionally, a correct upscaling procedure is specifically relevant for the transition into the industrial scale. All of these aspects are challenging because of the multiscale and multiphysics nature of these flows. In this paper we present a lower-order modeling strategy that aims to bridge the gap between fundamental research and applications by utilizing stochastic one-dimensional turbulence (ODT). Two case studies are performed. One is for two-way coupled turbulent Couette flow of electrolytes and another for one-way coupled planar Poiseuille flow in a wire-plate electrostatic precipitator. By comparison with reference data, we show that the modeling approach is robust and has predictive capabilities. Nevertheless, we also discuss some limitations of the purely one-dimensional and stochastic dynamical representation

Proton Spectra for the Interplanetary Space Derived From Different Environmental Models

Knowledge about the space radiation environment is crucial for the design and selection of materials and components used for space applications. This environment is characterized not only by the Sun’s electromagnetic radiation but also by charged particles categorized into solar wind, solar energetic particles (SEP) and galactic cosmic rays (GCR). Especially for material engineering and qualification testing, differential and integral spectra for particle energies ranging from keVs to GeVs are required. Up to now, a wide variety of models is available, whereas it is difficult to keep the overview. Although, e.g., the European Cooperation for Space Standardization (ECSS) standard includes instructions on how to investigate particle radiation, it does not provide an overall view. This paper shall support those in need of a comprehensive overview and provide comprehensive information about proton radiation spectra that can potentially be of use for space engineering tasks ranging from mission analysis to material and component design as well as qualification testing. The publicly accessible platforms OLTARIS, SPENVIS, and OMERE were examined for available proton spectra to be used. Exemplary, the particle radiation of solar cycle 23 is considered, which comprehends the years 1996–2008. A common drawback of the available models is their restriction to the MeV-range. Particularly when materials are directly exposed to the space environment, low energetic particles, specifically, the keV-range, are of high interest, since these particle transfer all their energy to the material. Therefore, additional data sources were used in order to include the usually neglected low energy protons into the derived spectrum. The data was transferred to common set of units and eventually could be compared and merged together. This includes a comparison of the most common models, incorporating data foundation, applicability, and accessibility. As a result, extensive and continues spectra are fitted that take all different models with its different energies and fluxes into account. Each covered year is represented by a fitted spectrum including confidence level as applicable. For solar active and quite times spectra are provided