XFlow – The CFD Simulation Code of the Future

...Published 2014-10-17

XFlow is a next generation CFD software system developed by Next Limit. It uses proprietary, state-of-the-art Lattice-Boltzmann technology to model transient aerodynamics, water management and fluid-structure interactions, to name a few.

Okay. So that was a condensed wealth of information – but what does it really mean?


The Lattice-Boltzmann technology that is referred to, is the embedded deadly-duo that makes the software so powerful. Unlike traditional CFD codes, XFlow makes use of a particle based mesoscopic (in-between micro and macro scale) mesh-free approach to solve the computational fluid dynamics. The Boltzmann equation is solved in a lattice structure, where each particle can transfer data in the lattice directions, as shown right.

This particle based lattice structure that represents the fluid domain is mesh-less. This feature of XFlow eliminates the tedious process of mesh refinement and generation usually associated with CFD software. Due to the nature of the computational domain structure; XFlow has the capability to simulate moving geometries (ridged body dynamics) and free surface flows. Large, complex geometries are not a limiting factor either – XFlow is tolerant to the quality of your geometry.


Figure 1: Panzer firing round

Simulation of moving geometries has been a considerable challenge in CFD in the past. CFD codes that make use of meshed fluid domains need to either stretch cells or re-populate the domain with new cells. The simulations can easily become unstable when this is done. One of the better approaches to modelling moving geometries was to approximate the motion by doing a series of simulations with the respective model in different locations. This proved to be very time consuming as the models needed to be re-meshed and solved separately.

Since XFlow does not make use of a mesh, moving geometry does not pose a problem to the solver. XFlow is capable of computing enforced motion or calculated motion (ridged body dynamics) with remarkable ease. This simulation of a round being fired from a panzer’s muzzle illustrates the capabilities of the software; shown in Figure 1 & 2.


Figure 2: Round release from muzzle

Another special case that XFlow handles very well is free surface fluid simulations. Free surface fluids are fluids such as water or oil, where there is a clear surface layer between the surroundings and the fluid. Figure 3 shows a simple simulation of a dam break. Separation of droplets from the main fluid body can be seen. XFlow also has a wave generator functionality for marine vessel simulations.

Not only can XFlow simulate moving geometries and free surface fluids, it can also simulate fluid-structure interactions. This is best explained with an example. A wind turbine can be simulated in XFlow to determine the efficiency or rotational speed of the rotor. A wind speed can be specified to be constant or to vary along a single or multiple axes. The rotor is constrained to be able to rotate freely about the axis normal to the flow. When the simulation starts, the rotor will begin to rotate due to the wind and the shape of the rotor blades. Similarly XFlow can simulate the response of a buoy due to water currents or wave shapes.


Figure 3: Free surface splash simulation of a dambreak

XFlow has a very easy to use top-down user interface. The model setup process is streamlined; allowing users to efficiently and effectively navigate the configuration environment, enabling your processors to get to number crunching as soon as possible. Once the computation has started, the user can start evaluating the results immediately. XFlow allows the user to begin full post processing as soon as the first time step has been computed.

XFLow is parallelized for multi-core technology, with near-linear scalability even with several hundred cores; which means that if you throw twice as much computational power at your simulation, it solves in almost half the time. Other CFD codes do not experience the same ratio and only marginal simulation speed up is achieved with massive core counts.

Ensuring that XFlow yields accurate results is evidently one of the developer’s top priorities. The software has been validated with some of the most complex case studies – such as the High Lift Prediction Workshop. Below is a video on the validation of the XFlow.

A company needs to make a serious commitment to a CFD code when it decides to start using it. Perpetual licences for CFD codes are very expensive. A great feature that Next Limit has incorporated into XFlow is that it can be used on a pay-per-use basis. Tokens can be purchased for the computational time and User Interface time required for the project. The CFD analysis cost can then easily be added to your project cost. The pay-per-use option is very affordable, and the tokens are valid for one year after purchase.

The unique characteristics of the XFlow technology breaks the limitations of the traditional methodologies – resulting in endless possibilities.

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