Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session D32: Applied CFD II |
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Chair: Catherine Gorle, Stanford University Room: Georgia World Congress Center B404 |
Sunday, November 18, 2018 2:30PM - 2:43PM |
D32.00001: Validating computational predictions of natural ventilation in Stanford’s Y2E2 building Chen Chen, Catherine Gorle Natural ventilation can significantly reduce building energy consumption, but robust design is challenging due to uncertainties in a building’s operating conditions. In a previous study, we used an integral model and a computational fluid dynamics (CFD) model with uncertainty quantification to model night-time ventilation in Stanford’s Y2E2 building. The prediction of indoor air temperature showed a too high cooling rate compared to building measurements; variance based sensitivity analysis showed that the initial thermal mass temperature and internal load had an important influence on results. The objective of the present study is to perform additional measurements to further investigate the discrepancies between the model predictions and measurements. Thermal mass temperatures are measured, and Bayesian inference is used to estimate the internal load. Extensive measurements of spatial variability in the indoor air temperature are conducted to support more accurate validation of the predictions. Future work will leverage the findings of this study to further improve the models and support robust design of natural ventilation systems. |
Sunday, November 18, 2018 2:43PM - 2:56PM |
D32.00002: Predictive simulations for quantifying ventilation in slum housing in Dhaka, Bangladesh Yunjae Hwang, Catherine Gorle Pneumonia is the leading cause of death in children under 5, killing 100 children every hour globally. Bangladesh is among the top ten countries with the highest incidence of pneumonia, and there are indications that improved ventilation in slum housing could reduce its occurrence. The objective of this study is to develop and validate a computational framework for predicting the ventilation rate in these slum houses. The framework uses a combination of an integral model, a computational fluid dynamics (CFD) model, and uncertainty quantification methods. The integral model is used to quantify the effect of uncertainties in model parameters such as weather conditions, the home’s material properties, the internal heat loads, and the window discharge coefficients, on the prediction. The 3D CFD model is used to investigate local flow patterns and obtain more accurate inputs used in the integral model. Validation is performed by comparing model predictions to ventilation measurements performed in a Dhaka home. The validated model will be used to design an optimal solution for improving ventilation while maintaining thermal comfort and mitigating privacy and safety concerns. |
Sunday, November 18, 2018 2:56PM - 3:09PM |
D32.00003: Converting visually realistic L-System tree models into a porous media model for urban CFD Daniel Joseph Wise, Woei Leong Chan, Chi Wan Lim, Like Gobeawan, Yongdong Cui, Hee Joo Poh As part of the Virtual Singapore (VS) initiative, steps are being taken to populate Singapore's digital twin with visually accurate tree models. The most detailed of these are created using Lindenmayer or L-Systems which accurately capture biological features such as branching angles, trunk/branch growth rates, and leaf fall rates. As Singapore is home to over 2 million trees, many of which are located in urban areas, it is imperative that they are modelled with sufficient accuracy when CFD analyses are performed. |
Sunday, November 18, 2018 3:09PM - 3:22PM |
D32.00004: High-Performance CFD Validation of GPPH Planing Hull in Calm Water Mostafa Elaskalany, Motiur Rahman, Maysam Mousaviraad The Generic Prismatic Planing Hull (GPPH) is a representative geometry of typical planing hulls that is designed as part of an Office of Naval Research project to obtain a comprehensive set of experimental data for assessing of CFD tools. The purpose of the current work is validation studies using OpenFoam for GPPH in calm water. The Froude numbers range from 1.14 to 2.51 and the boat is free to heave and trim. The experimental data and uncertainties for resistance, heave, and trim at four different speeds were used as a CFD grand challenge at the recent MACC 2018 conference. Ten different submissions were made which included potential flow, boundary element, LBM, and URANS solvers. Herein, we present OpenFoam results and provide a comparison with the previous simulations. The simulation uncertainty intervals and the state of the art validation uncertainties are determined accounting for the experimental uncertainty and the numerical uncertainty. Simulation uncertainties include the uncertainty due to the different simulations similar to the facility bias for experiments. The current state of the art for planing hull is summarized and compared with the previous studies for conventional hulls at lower speeds. Future studies will include motions and slamming pressures in waves. |
Sunday, November 18, 2018 3:22PM - 3:35PM |
D32.00005: LES- and RANS-based Modeling of Coupled Flow & Mobile bed Evolution in a Natural River Under Various Flood-induced Turbulent Boundary Layers Ali Khosronejad, Kevin Flora Flow field and sediment transport in rivers under flood conditions are dominated by high-energy, large-scale, coherent structures. High-resolution numerical modeling provides a reliable tool to better understand the flow and bed morphodynamics interaction. The inlet turbulent boundary layers (TBL) used to prescribe the incoming turbulence in natural rivers can have crucial effects on the flow and sediment dynamics. We employ an in-house CURVIB code, the VFS-Geophysics, to systematically investigate the effect of various TBLs on the LES and unsteady RANS computed flow and morphodynamics of a 0.6km-long area of the Feather River in California under flood condition. We employ three different TBLs, including: a uniform flow, a precursor straight-channel flow simulation, and a precursor river-flow simulation in a 1km-long area of the river immediately upstream of the study area. The pre-flood bathymetry is utilized to produce the computational grid system of the river. While, the post-flood bed bathymetry served as a benchmark to validate the computed bed morphodynamcis calculations. |
Sunday, November 18, 2018 3:35PM - 3:48PM |
D32.00006: A new algebraic turbulence model for simulating hypersonic boundary layer transition. Wei-Tao Bi, Mengjuan Xiao, Zhen-Su She We report a new algebraic turbulence model (SED-SL) based on a structural ensemble dynamics (SED) theory of wall turbulence (She et al., 2017). The model specifies a multi-layer profile of a stress length (SL) function (which defines the eddy viscosity) in both the streamwise and wall-normal directions, characterizing the laminar-turbulent transition on a wall. First, we report clear evidence of a successful simulation of flat-plate compressible TBLs by the SED-SL model (She et al., 2018). Then, we report further applications of the model to the hypersonic boundary layer transition on a straight cone at Mach 6. The SED-SL model predicts correctly the mean surface heat fluxes during the transition processes for all the experimental cases (Horvath, 2002), superior to other closure models. Remarkably, the transition peak and the subsequent relaxation to the fully developed turbulent flow is accurately simulated. The most important achievement is the physical interpretation of the model parameters: they specify the differentiating multi-layer structures of TBLs with well-behaved parameter variation; consequently, the model delivers high simulation accuracy for all cases, and specifies the physics of CTBL for varying flow circumstances. |
Sunday, November 18, 2018 3:48PM - 4:01PM |
D32.00007: A new algebraic turbulence model for the prediction of three-dimensional aeronautic flows. Mengjuan Xiao, Zhen-Su She, Wei-Tao Bi We report a new algebraic turbulence model (SED-SL) based on a structural ensemble dynamics (SED) theory of wall turbulence (She et al., 2017), a symmetry-based approach to quantifying wall turbulence. The model specifies a multi-layer profile of a stress length (SL) function in both wall-normal and streamwise direction, validated by empirical data from both experiments and simulations. After a successful simulation of transitional flat plate flows (APS meeting, 2016) and further applications to the flows over airfoils (APS meeting, 2017), we here report the results of its application to three dimensional flows over M6 wing and DLR-F4 wing/body. For the flow over M6 wing, the prediction of the Cp by simplified version of the SED-SL model has comparable quality to SA and SST model, but with much less complexity in parameter setting and computing time. For the flow over DLR-F4 wing-body, a significant improvement of the prediction accuracy of CL and CD is obtained with SED-SL, compared to SA and SST. Future applications of the SED-SL model to aeronautic flows would not only provide accurate prediction model for assisting aeronautic design, but also yield more knowledge about the flow physics. |
Sunday, November 18, 2018 4:01PM - 4:14PM |
D32.00008: Low Reynolds number airfoil dynamics: three different flow patterns within a small range of angles of attack Bjoern F. Klose, Gustaaf B Jacobs, Joseph D Tank, Geoffrey R Spedding The effect of angles of attack on the flow over of a NACA 65(1)-412 airfoil at low Reynolds number is investigated. Direct numerical simulations in two and three dimensions are performed using a discontinuous-Galerkin spectral element method. Through analysis of lift, drag, and pressure coefficients, average velocity field, and Lagrangian Coherent Structures determined by the Finite-Time Lyapunov Exponent, we show that the flow bifurcates several times in a small range of angles of attack. The flow is in a laminar separated state with transition to turbulence in the wake for angles smaller than 7°. Increasing the angle leads to laminar reattachment of the flow at 8° incidence. Then, for angles of attack larger than 8° the separation bubble bifurcates to a sizable bubble at the leading section of the airfoil, followed by transition to a fully turbulent flow. At an angle of attack of 8°, a high lift coefficient at low drag marks a preferable state in terms of aerodynamic performance of the airfoil. |
Sunday, November 18, 2018 4:14PM - 4:27PM |
D32.00009: Numerical simulation of an unsteady flow over a circular cylinder at high Reynolds numbers Nariman Ashrafi, Seyed Mahmood Kia Flow around bluff bodies such as a circular and elliptical cylinder is a challenging problem in fluid mechanics. Many engineering applications such as offshore structures, bridge piers, and pipelines can be modeled as a circular cylinder. In the present study, unsteady flow around a circular cylinder is simulated by ANSYS-Fluent 14.0 in laminar and turbulent flow regimes. The Finite Volume Method with second-order equations were applied. The coupling of pressure and velocity equations solved by the PISO algorithm. The PISO algorithm is more accurate in transient flows, also it shows vortices behind of cylinder clearer than other methods. Owing to the capability of the k-ε turbulent model, it is used in this study. In the simulation, the effects of Reynolds number’s changes on the formation and destruction period time of vortices and drag and lift coefficient have investigated. The results showed that by increasing the Reynolds number, the time of formation and destruction of vortices, as well as lift coefficient has experienced a decrease. The drag coefficient fluctuated and the overall trend was decreasing. It is crystal clear that the simulation results are in good agreement with previous results which the numerical error of the lift and drag coefficients were less than 10%. |
Sunday, November 18, 2018 4:27PM - 4:40PM |
D32.00010: Flow Past a Circular Cylinder on a 2D Curved Surface Using Discrete Exterior Calculus Pankaj Jagad, Mamdouh Mohamed, Ravi Samtaney We present results of flow past a circular cylinder embedded on a curved 2D surface using the approach of discrete exterior calculus (DEC) (Mohamed et al., Journal of Computational Physics, 312, 175-191, 2016). DEC has been demonstrated to exhibit good conservation of secondary flow quantities such as kinetic energy (for inviscid flows) and discretely satisfies vorticity conservation both locally and globally. Moreover, DEC is suitable for studying flows |
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