High fidelity numerical simulations of ship and sub-marine hydrodynamics

This paper discusses the use of wall-modeled LES and hybrid RANS-LES models for the prediction of ship and submarine flows. Results from applied cases are discussed to il-lustrate the use of these methods for practical problems as well as the differences between methods. The paper then discusses the underlying theories and assumptions of wall-modeled LES and hybrid RANS-LES models. The focus of this presentation is on wall-modeled LES as these methods are theoretically more well-founded than hybrid RANS-LES models. Re-sults from both canonical and building block flows are then presented and discussed in order to provide a more firm and practical foundation for the recommendations for applied use that are provided in the final concluding remarks section

Inlet conditions for LES using mapping and feedback control

Copyright © 2009 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Computers and Fluids. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Computers and Fluids, Volume 38 Issue 6 (2009), DOI: 10.1016/j.compfluid.2009.02.001Generating effective and efficient inlet boundary conditions for large eddy simulation (LES) is a challenging problem. The most accurate way of achieving this is to run a precursor calculation to generate a library of turbulence, either prior to the simulation or concurrently with it, and to transfer the data from the library simulation to the main domain inlet. In this paper, we investigate a variant of this, in which the precursor calculation is subsumed into the main domain, its function being adopted by a mapping of data from a specified plane downstream of the inlet back to the inlet. Within this inlet section of the main domain, the flow can be affected by a number of computational manipulations, including the introduction of artificial body forces, modification of the mapped data, and direct correction of the velocity data. These modifications can be linked to feedback control algorithms to drive the solution towards specified characteristics, including mean and turbulent flow profiles, and bulk properties of the flow such as swirl. Various variants of the basic technique incorporating different levels of complexity in the control are implemented and tested on simulation of flow in a rectangular channel and in a circular pipe

Large Eddy Simulations of Fully-Developed Turbulent Pipe Flows At Moderate-To-High Reynolds Numbers

Despite the high relevance of wall-bounded turbulence for engineering and natural science applications, many aspects of the underlying physics are still unclear. In particular, at high Re close to many real-life scenarios, the true nature of the flow is partially masked by the inability of numerical simulations to resolve all turbulent scales adequately. To overcome this issue, we aim to numerically investigate fully-developed turbulent pipe flows at moderate-to-high Re ($361 \leq Re_\tau \leq 6,000$), employing LES. A grid convergence study, using the WALE subgrid stress model, is presented for $Re_\tau=361$. Additionally, the prediction accuracy of distinct subgrid-scale stress models, such as WALE, SMG, OEEVM, LDKM, and DSEM, is examined using a range of statistical measures. The results infer, as expected, that SMG and OEEVM are too dissipative, whereas WALE, LDKM, and, more surprisingly, DSEM perform rather well compared to experiments and results from DNS. Moreover, LES utilizing WALE are performed and investigated in detail for six different Reynolds numbers in the interval from $Re_\tau = 361$ to $6,000$ with gradually refined grids. These computations allow an insight into what turbulence information is retained when LES with a wall model is applied to such high Reynolds numbers in the limit of a relatively coarse grid. Second-order statistics for all values of $Re_\tau$ exhibited excellent agreement with the DNS data in the outer region. Surprisingly, results also revealed a dramatic deviation from the DNS data in the sub-viscous layer region irrespective of the $Re_\tau$, attributed to the considered scaling for mesh refinement. Overall, the WALE model enabled accurate numerical simulations of high-Reynolds-number wall-bounded flows at a fraction of the cost incurred if the inner layer was temporally and spatially resolved

Industrigolv.

This paper deals with cracking in industrial concrete floars. We have restricted us to study two special cases, that is, eraeks developed by the load itself and eraeks due to shrinkage. We have of course also studied the deformation effects of the load. The effect of the load has here been studied thoroughly by two separate methods, Winklerfoundation and the more exact Elastic halfspace theory. We have also studied effects eaused by two separate loads at a distance. The shrinkage is dealt with in accordonance with a paper from Buö (11) who has studied this problem extensivly. Our purpose has been to establish designing aids for this type of pavements. These are quite extensive and are based on the regulations for concrete structures BBK 79

A Fluid-Dynamical Subgrid Scale Model for Highly Compressible Astrophysical Turbulence

We formulate and implement the Euler equations with SGS dynamics and provide numerical tests of an SGS turbulence energy model that predicts the turbulent pressure of unresolved velocity fluctuations and the rate of dissipation for highly compressible turbulence. We test closures for the turbulence energy cascade by filtering data from high-resolution simulations of forced isothermal and adiabatic turbulence. Optimal properties and an excellent correlation are found for a linear combination of the eddy-viscosity closure that is employed in LES of weakly compressible turbulence and a term that is non-linear in the Jacobian matrix of the velocity. Using this mixed closure, the SGS turbulence energy model is validated in LES of turbulence with stochastic forcing. It is found that the SGS model satisfies several important requirements: 1. The mean SGS turbulence energy follows a power law for varying grid scale. 2. The root mean square (RMS) Mach number of the unresolved velocity fluctuations is proportional to the RMS Mach number of the resolved turbulence, independent of the forcing. 3. The rate of dissipation and the turbulence energy flux are constant. Moreover, we discuss difficulties with direct estimates of the turbulent pressure and the dissipation rate on the basis of resolved flow quantities that have recently been proposed. In combination with the energy injection by stellar feedback and other unresolved processes, the proposed SGS model is applicable to a variety of problems in computational astrophysics. Computing the SGS turbulence energy, the treatment of star formation and stellar feedback in galaxy simulations can be improved. Further, we expect that the turbulent pressure on the grid scale affects the stability of gas against gravitational collapse.Comment: 19 pages, 16 figures, submitted to A&

LARGE EDDY SIMULATION OF A FORWARD-BACKWARD FACING STEP FOR ACOUSTIC SOURCE IDENTIFICATION

The feasibility of using a commercial CFD code for large eddy simulation (LES) is investigated. A first test on homogeneous turbulence decay allows a fine-tuning of the eddy viscosity with respect to the numerical features of the code. Then, a flow over forward–backward facing step at Reynolds number Reh 1:7 105 is computed. The results found show good agreement with the new LDA data of Leclercq et al. [Forward backward facing step pair: aerodynamic flow, wall pressure and acoustic characterization. AIAA-2001-2249]. The acoustic source term, recorded from the LES and to be fed into a following acoustic propagation simulation, is found to be largest in the separation from the forward step. The source terms structures are similar to the vortical structures generated at the front edge of the obstacle and advected downstream. Structures generated from the backward step rapidly break down into smaller scale structures due to the background turbulence

Study of the influence of the inlet boundary conditions in a LES simulation of internal flow in a diesel injector

In this paper the study of the behavior of the fuel flow through the injector nozzle using CFD tools is presented. Large Eddy Simulation will be used to model the internal flow turbulence in a Diesel fuel injector with velocities over 500 m/s. More specifically, the influence of boundary conditions applied to the model will be studied. The article analyzes the influence of the inlet boundary condition upon activation and maintenance of turbulent flow during the calculation. Carefully assessing which inlet boundary condition is more trustworthy in reality, for this the outlet velocity, pressure, turbulence and level of stabilization will be studied.This work has been funded by UNIVERSIDAD POLITECNICA DE VALENCIA from Spain, in the framework of the project "ESTUDIO DE LA INFLUENCIA DEL LEVANTAMIENTO DE AGUJA EN EL PROCESO DE INYECCION DIESEL'', Reference No. PAID-06-10-2362.Payri Marín, R.; Gimeno García, J.; Marti Aldaravi, P.; Bracho León, GC. (2013). Study of the influence of the inlet boundary conditions in a LES simulation of internal flow in a diesel injector. Mathematical and Computer Modelling. 57(7-8):1709-1715. https://doi.org/10.1016/j.mcm.2011.11.019S17091715577-