New developments in FLOW-3D version 10.1 include the hybrid shallow water/3D flow model, the addition of porous moving components to the general moving objects model, the addition of a spray cooling model, plastic deformations in the FEA model and a new model for cooling channels. Version 10.1 features extensive improvements to the accuracy and performance of the software, including a dramatic reduction in the size of the results files. In addition to the solver developments, there has been a major redesign of the graphical users interface to help users easier unleash the power and accuracy of FLOW-3D.
New Models and Features
The hybrid shallow water/3D flow model in FLOW-3D is designed to model flow around 3D structures within a ‘shallow water’ environment, such as bridges, drilling rigs at sea and dams in large reservoirs. The model uses multi-block meshing, where a mesh block is designated as shallow water or 3D. The standard shallow water or 3D equations are solved within each such block, based on the user selection, and the respective solutions are coupled at the block boundaries.
Figure 2. Flooding of a large area with flow originating at a weir. The weir is modeled in a 3D mesh
block linked to a shallow water block that contains the flood area downstream.
Click the image to see a flooding animation.
Fluid-Structure Interaction (FSI) and Thermal Stress Evolution (TSE) models
Plastic strain magnitude of a cast aluminum
V6 engine block after 20 min cooling.
Temperature-dependent yielding, based on the von Mises yield criterion, and plastic deformations (without hardening) have been added to both the FSI and TSE models. This addition is especially important when modeling the development of residual stresses in solidifying metals.
An optional pre-conditioning step for the iterative FEA solver may help achieve more accurate solutions in less time.
Dynamic sub-space size
The option to dynamically adjust sub-space size for the iterative GMRES solver is designed to achieve convergence in less time.
FLOW-3D's new cooling channel model offers a wide range of controls, including time-dependent temperature and heat transfer coefficients and time- and temperature-controlled activation, allowing for many different types of cooling lines. These features allow the user to accurately capture the complex behavior of modern systems, assuring an optimum design and casting properties. The user has three options to control cooling channels: on and off with respect to time, temperature control (thermocouple) or the cooling lines can remain on throughout the duration of the simulation. This model will help in the setup of die cycling where cooling lines may be on only during the first stage (solidification).
This simulation shows a slice through the die, colored by the wall temperature, for 10 cycles.
The slice was chosen to show the core cooling channels on during the first stage and off
during the other stages in a cycle.
Liquid/Gas Phase Change
The two-fluid, gas/liquid phase change model with a non-condensable gas component has been extended to include spray cooling, where liquid droplets are represented with Lagrangian particles. The particles interact with the surrounding gas through heat transfer and phase change, and are absorbed into liquid once they enter it. The model also includes a special type of particle source called ‘spray bar’ in which liquid droplets are emitted from small holes in a cylindrical channel at a prescribed rate.
Liquid spray reduces gas temperature from 222 to 207 F in 50 seconds
Initial and boundary conditions for the vapor/gas mixture can now be defined in terms of relative saturation, as an alternative to the existing non-condensable gas volume fraction. This is especially useful when modeling water vapor in air.
Saturation curve and latent heat
Tabular and polynomial definitions of the P — T saturation curve and the latent heat as functions of temperature have been added to the liquid/gas phase model as an alternative to the existing Clausius-Clapeyron equation for the P — T curve and constant latent. This addition expands the applicability of the phase change model in the range of temperatures from the triple point to the critical one.
Water fills pore space in
an upward moving object.
GMO components can now be porous and move in a prescribed or fully coupled fashion. At each time step, the volume and area fractions are updated in all the mesh cells occupied by the porous objects. The drag force of the porous media on the fluid is computed using the relative velocity between the object and the fluid. Porosity effects are also considered in the calculations of hydraulic forces and torques exerted on the moving objects. Applications of this new model include simulating engine flooding, floating breakwaters, and floating tires. Read more in the Development Focus: Improvements to the General Moving Objects Model
Automatic Fluid Volume Correction
An option has been added to automatically maintain a constant volume of fluid #1 to compensate for possible systematic volume errors due to severe distortion of free surface. The model is especially useful in confined flows such as fluid sloshing in a fuel tank or oil churning in a gear box.
Fluid Initial Conditions
General hydrostatic pressure
A general hydrostatic pressure solver has been developed to replace the old simplified linear solutions. The solver works for complex geometries, two-fluid mixtures, fluids with variable density and with the non-inertial reference frame motion model.
Restart fluid regions
A new type of initial fluid regions has been introduced to be used in restart calculations. These regions allow users to modify the initial conditions read from the restart data source files, for example, to insert a bubble or a droplet into the solution.
Implicit Free Surface Pressure
An option to treat free surface pressure implicitly has been added to help speed up one-fluid, free-surface flow simulations by eliminating the time-step size stability limit associated with free surface boundary (stability code ‘fs’).
Gravity and Non-Inertial Reference Frame (NIRF) Model
The definition of gravity has been separated between cases that use constant gravity (IACCF=0) and the NIRF model in which gravity direction may change with time, to eliminate confusion during problem setup.
Two-phase Drift-flux Model
The ability to define the minimum and maximum volume fractions of dispersed phase has been extended to two-fluid cases.
The gas venting model that previously worked only with one-fluid, adiabatic bubble option, has been extended to work with two-fluid compressible fluid model as well.
External Sources for Tabular Material Properties
Temperature-dependent material properties of fluids and geometry components can be read directly from external comma-, space- and tab-separate ASCII files, without copying them into the prepin file. This feature eliminates the need to reimport the data into the simulation when the properties are changed.
Time step threshold example: Aluminum high pressure
die casting filling, fill time 0.5 sec. Using the target
time-step size of 0.4 ms, reduce the run time by 40%.
The implicit advection solver has been enhanced to allow the user to define a threshold velocity or time-step size to directly control the use of explicit and implicit approximations of advective fluxes. The goal of this addition is to speed up simulations by maintaining a larger time-step size than in a fully explicit run, but small enough (based on the user’s judgment) to resolve the essential features of the flow.
Volume Fraction Cleanup
The volume fraction cleanup option allows users to force the preprocessor to close small openings between solid components that sometimes appear due to minor inaccuracies in the STL data. Barely open cells could pose problems for the stability of the flow solution, but at the same time are usually not important.
Short Print Interval
In addition to the existing short print interval for the output to the hd3msg file based on the total simulation time, it now also depends on the clock time, with the default being 2 minutes. This addition ensures more regular and frequent updates of the solver status during long running simulations.
Fluid Restart Overlay
The standard solution overlay procedure during restart uses the volume-of-fluid (VOF) function, F, to locate and interpolate fluid interfaces. However, when geometry is modified at restart, specifically, when a solid component is removed thus exposing adjacent fluid to void, then the fluid interface is better described with the product of the VOF function and the volume fraction, V F, providing a more accurate solution overlay. This has been added as an option to the current list of restart features.
Orthotropic Thermal Conductivity
Thermal conductivity in solids made of thin layered materials, such as composites, may be highly anisotropic. The new feature allows users to defined different rates of thermal conduction in a geometry component along the orthogonal coordinate directions (hence the name orthotropic).
Implicit Pressure Solvers
Minimum number of iterations
The user can now define the minimum number of pressure iterations to be able to achieve better convergence by increasing it, as an alternative to reducing the convergence criterion.
Dynamic sub-space size
The option to dynamically adjust sub-space size for the iterative GMRES pressure solver is designed to achieve convergence in less time.
FL and TEMP Namelist Merge
The input namelists in the prepin file that define the initial fluid (FL) and temperature (TEMP) conditions have been merged into one (FL) to improve the efficiency and accuracy of setting the initial conditions. The old input files will be automatically converted to the new format when they are first opened in the GUI.
CAD Data Input
Support for ANSYS and I-DEAS CAD data has been discontinued. Only STL geometry data input is now supported. Topographical data files must be converted to STL format using the provided conversion tool under the Utilities menu in GUI’s Meshing & Geometry tab. The resulting STL file can then be imported into the simulation.
Simulations can now be terminated based on the number of time steps, in addition to the existing finish time and other termination criteria.
An input variable for the universal gas constant has been added to the core gas model. Together with the Stefan-Boltzmann constant, used in the radiative heat transfer model, the default value of this variable is automatically set based on the user-defined unit system.
The potential defects arising from metal oxidation and lost foam residue are now generated and tracked separately from each other, described as free surface and foam residue defects. This change helps to better identify the origin of defects in lost foam castings.
Spinning and Fan/Impeller Components
The definition of axisymmetric spinning components and fan/impeller components has been simplified to eliminate the need to create copies of virtual components. The axis of rotation is now directly defined by the user using two points. The removal of the copy requirement also allows users to define these geometric objects using STL data.
Contact Angle Function
A user-customizable FORTRAN function cangcal has been added to the solver to allow users to easily add their own descriptions of the fluid/solid contact line behavior.
Number of Processors
The number of processors that the user requests for a simulation in the GUI’s General tab is written to the prepin file as the variable NPROCS, and is then used by the solver if the simulation is subsequently run from the command line. Previously, the number of processors in that case would be based on the environment settings, which is still the case if NPROCS is not present in the prepin file.
History probes can now be of two types – fluid and FSI/TSE. The former works as the standard probe feature, outputting solution quantities computed in the structured grid. The new FSI/TSE probes output the solution of the stress/strain equations computed in the Fluid-Structure Interaction and Thermal Stress Evolution models. These probes must be placed within the finite-element mesh.
Probes inside the FE mesh for FSI and TSE simulations, similar to fluid probes in the structured mesh.
Users can output turbulence intensity in FLOW-3D v10.1.
Two new spatial quantities have been added to the turbulence model output. The first one is y+ that is helpful in evaluating the turbulent boundary layer resolution near walls, and the second one is turbulence intensity in %, with the value of 0.0 meaning laminar flow, that is useful in estimating the level of turbulence in different parts of the flow, for example, during mold filling.
Output File Format
Only the active mesh is now written to the flsgrf file, helping to reduce its size compared to the previous format where the whole mesh was stored. The file size reduction is proportional to the ratio of the active and passive mesh cell counts. Additionally, the solution in all mesh boundary cells is also saved and can be viewed in the GUI’s Analyze tab by modifying the spatial plot limits in the flsinp.tmp file.