GOOD NEWS: The new version, Fluids6, supports multiprocessing (up to 8 processors), so it is several times faster. It also supports models with better resolution, up to 400 layers along the duct.
NOTE: Fluids6 can import STL files and calculate forces
FLUIDS6 : better resolution, multiprocessing
New example: http://www.raczynski.com/pn/fluidsex1.htm
This is the new version of the Fluids package. The old Fluids5 program is no longer distributed. Model files of both Fluids5 and Fluids6 have the same format, so you can import your old models to Fluids6.
What is new:
Multiprocessing: New PCs are now equipped with more powerful , normally dual or quad processors. Consequently, new software should be designed to run on multiple processors. Fluids6 detects automatically the processors, and runs its simulation procedure on all available processors concurrently. This means that you can achieve a considerable speedup, approximately proportional to the number of processors. On the other hand, if you use full resolution of Fluids6, the number of grid points may be rather big, which means that the simulation will slow down. While creating a model, you always should think about a reasonable compromise between the model resolution and the computing time. Of course, if you have a single processor machine, then Fluids6 will run on one processor and you will be able to process your old Fluids6 models as well.
Resolution: Fluids6 permits up to 400 layers in the main duct direction (Z-axis). The resolution in X and Y can also be greater, so the total number of grid points is 8 times greater comparing with a similar model with 200 layer resolution. The figure below shows the comparison of these two resolutions.
The upper figure shows the resolution of Fluids5, the other was taken from a screen of Fluids6
A model with 390 layers
Velocity field for the 390 layers model. Vertical section. Total grid points 867088.
The augmented resolution permits to create ducts and obstacles with more precision. Both the duct length (Z-axis) and the X-Y-size may have two times more grid points. This is due to the permitted duct length. While drawing the duct, the recommended drawing area reflects this change. Remember that this means about 8 times the number of 3D grid points. While a reasonable number of grid points for Fluids6 was of 50,000 (after reducing the number of points), this may grow to more than 500,000 (1,500,000 to 2,000,000 before the automatic reduction) in Fluids6. Anyway, you always can edit a "low resolution" models. To do this, just define your duct using only half length of the recommended drawing area. This will result in less than 200 layers in Z direction. For big, 400-layers models you can reduce the resolution if you feel the number of points is too big (more than 1 million), using the Edit Shape - Reduce resolution option of the main menu.
The other important enhancement is multiprocessing. New PCs frequently are equipped with two, four or eight processors, so it is important that the new software can use this advantage. Fluids6 detects automatically the number of processors available, and performs the flow calculations on the maximal number of processors. As the result, you get a considerable speedup, approximately N times, with N processors. On the other hand, if you define a higher resolution model with thick duct, then the number of grid point in 3D space may be rather big, which slows down the simulation. The reasonable number of (fine) grid points is up to 1,500,000. After reducing the number of points, this still remains big, may be several hundred thousand.
Note that to simulate big models with Fluids6 you need a fast machine with multiple processors. The minimal recommended platform is double or quad processor, 2.4 GHz, 2GB of memory, at least 10 GB of hard disk space available. The model files are also big, normally more than 100 MB.
To be able to use the new features of Fluids6 you must have a fast machine and the multiple-processor PC is recommended. The good results can be obtained on a double-core or quad 2GHz processor or faster, at least 2GB of memory. You will also need hard disc space enough to store the projects. A typical low-resolution Fluids6-like project may need 20MB, a normal Fluids6 project will need 100MB or more. The minimal screen resolution is 1024x768.
Anyway, if you have a smaller machine, you can use Fluids6 just like Fluids6. Comparing to the old Fluids6 program in low resolution mode, several improvements been introduced.
How it works:
Fluids6 solves the Navier-Stokes (N-S) equation for a gas
or an incompressible liquid that flows through 3D channels with
obstacles. The channel and the obstacles can be arbitrary 3D shapes.
Optionally, the channel may be axisymmetric. See some examples
of gas flow analysis at the end of this page.
Recall that the N-S equation is a nonlinear partial equation that describes fluid dynamics. The N-S equation is complemented by the continuity equation. The whole system represents a set of nonlinear partial differential equations with four unknown variables assigned to each point of the a 3D region: the pressure and the three components of the particle velocity.
This is a dynamic solution, rather than a search for a steady state solution. Perhaps steady solution is a nice one, shown in books on fluid dynamics and calculated by many fluid dynamics programs. However, it has rather academic and not practical meaning. The steady solution may exist if the flow is laminar (with low velocity) or if its behavior and properties are very "regular". In a real flow, particularly for gases, no steady solution is reached in the real flow, unless the velocities are low. The pressure and velocity fields constantly change and the flow is oscillatory or it becomes chaotic. Fluids6 provides such a dynamic, time-dependent solution that can be useful while simulating shock waves, oscillations in valves or nozzles or similar problems. However, the steady solution option has been added in the new versions 5 and 6. It works for the liquid case only and with very low pressure differences.
It should be noted that to obtain a dynamic
solution, even for few
milliseconds of the transient process, you need a long
computing time; in less than half hour of computer time you will get
nothing interesting. A normal simulation time oscillates between on
hour to several hours on a
fast (more than GHz) machine. But it is necessary, no program can
simulate a 3D liquid flow model with 300,000
grid points in few minutes. Sometimes after one or two hours you
merely reach a millisecond of the model time. Long simulations can
provide something similar to steady solution, but remember that the
main application of Fluids6 are shock waves. As for the "steady
solution" note that in the real flow a steady state does not
exist, unless you have very low pressure gradient and velocities. But
such solutions are not very interesting, they are rather academic
examples. In a real flow the velocity field is always changing,
oscillating or produces turbulence. So, the Fluids6 program never
stops, it has not "stop criterion". This is a dynamic
simulation, where each iteration step provides an image of the
velocity, pressure and temperature fields for a particular model time
The flow is considered to occur in an axisymmetrical or irregular channel that has an inlet and outlet. However, the user can define any other configuration, like, for example, an open region where some internal points have fixed pressure, being sources of the flow. The boundary conditions are defined as sets of points with fixed pressure or fixed velocity. It is supposed that the velocity on all solid boundaries is fixed. Moving walls of the duct or obstacle are also supported. The pressure at the inlet/outlet points can be defined by the user, as an external excitation.
Fluids6 program includes a 3D duct editor. The duct shape is defined graphically. For the axisymmetric duct the user draws the duct projection. For the arbitrary duct the shape is defined by sections (layers) on the X-Y plane, that are given consecutive Z coordinate values. Then, the program creates the set of grid points to discretize the problem in space. A normal channel needs about 500,000 points. For each point the pressure, the temperature (gas case) and the three velocity components are calculated.
Fluids6 can calculate the forces on the duct walls and/or obstacles, produced by the flow.
Fluids6 can import STL ASCII files created by CAD/CAM software or other 3D graphics programs. So, you can import a duct or obstacle shape instead of editing it with the Fluids6 shape editor. The "slicer" algorithm of Fluids6 converts an STL file in up to 400 slices that define the 3d duct shape. The "slicer" resolution is limited to those 400 layers, so small details of complicated shapes can be lost. But this option enables you to create shapes that may hardly be edited by Fluids6 itself.
The Fluids6 display screens show the 3D or 2D channel and obstacle images with variable view angles. The following result images are provided.
Velocity in a vertical (Y-Z), horizontal (X-Z) or X-Y projections. The velocity is marked at each grid point as a section which direction shows the particle velocity direction. The length of the velocity indicator may be constant or proportional to the absolute velocity, and the color changes with the velocity.
Pressure marked at each point with a corresponding color
Rotation marked with a corresponding color. The rotation is the sum of the absolute values of the components of the rotation tensor
Flow lines in X-Z, Y-Z and X-Y projections, and the 3D image of flow lines that start from random points inside the duct. This image can be seen from different angles, providing an illustrative image of the flow behavior.
PLATFORM: PC min 2GB RAM, and a fast 2GHZ or more machine is recommended. Windows 98 or later, NT, XP Vista.
The examples shown below have mostly been obtained using Fluids5. They are shown here, because the lower resolution flow images look better on a Web pages. Exactly the same sesults can be generated by Fluids6, the only difference is two-times better resolution of the model grid. As stated before, the other main advantage of FLuids6 is the computing speed. Compared to Fluids5, Fluids6 may be up to 9 times faster while running the same model on an 8-processor machine.
Example - liquid flow
This image shows an axisymmetric channel with two obstacles.
The above figure shows the velocity distribution in the Y-Z projection (a section of the channel with a vertical plane X=0). Remember that the model is 3-dimensional, and the above image shows only one section of the duct. The whole problem includes more than 60000 grid points. It is a liquid flow with external presure applied at the left side of the duct, the right side being open. The length of the velocity sections is proportional to the logarithm of the velocity. The velocity is also marked with different colors: blue sections represent low velocity, while the yellow means big velocity.
Below are some images taken from a simulation of air excited by a short pressure pulse at the left end of a duct with an obstacle. The first image shows the moment when the front of the shock wave bounces for the first time from the obstacle. The next picture shows the situation after some longer time interval. On the last figure we can see the pressure distribution in a vertical section of the duct in the same moment of the model time. Also the temperature of the gas is plotted in similar way.
WAVES IN GAS AND FREQUENCY ANALYSIS
As the gas flow simulation is dynamic, you can see the time-plots of the pressure in selected fixed points. Frequently the multiple reflections result in oscilations, like in musical instruments. In these cases it is very interesting to see the frequency response of the model. The frequency analysis option of Fluids32.3 does the job. The user can see the spectrum of the gas vibrations in the selected points inside the duct.
CONVECTION in GAS
Some parts of duct and obstacle walls can be given a fixed, user-defines temperature. This results in slow clonvection gas movement. As the velocities of the convection related movements are low, this fenomemnon can be observed when no other strong excitations are defined. The below images illustrate the convection flow. A part of the right-hand side of a vertical duct is heated (red line on the right side indicated the heated region). The first figure shows the velocity distribution and the second shows the temperature several seconds after the temperature pulse have been applied.
Below is another example of slow convection velocity field in gas (a 2D section of a 3D model). The heated area has 420 degree Kelvin and the elliptic body has 150 Kelvin. The color indicates velocity, not temperature. The air cooled by the cool body falls down, and the heater generates the upwards flow. Anyway, the air near to the body goes down.
An example of an unstable stream of air. Made with the new version of the program, Fluids6.
Note that symmetrical ducts and boundary conditions does not lead to symmetrical flows. See http://www.raczynski.com/pn/fluidsex1.htm
An interesting fact is the oscillating character of the flow. The following plot shows the pressure oscillation below the wing.
Other example of oscillating gas flow. Pressure waves in a gas flow through a chamber. No steady solution in this case exists.
The following figure shows another simulation of the chamber flow
The following figure shows the air flow around a space capsule which enters the atmosphere.
In the above model the main duct was a cylinder, and the whole geometry as well as the boundary conditions have been ax-symmetrical. However, the resulting 3D velocity field in not.
Other example: A tube with an appendix (figure below).
Water enters at the left and passes through the duct. It is interesting that a vortex forms not only in the appendix, but also in the tube. The amazing flow lines are shown below. White arrows show the parts where a counterflow occurs.
Download it from http://www.raczynski.com/pn/updfl.htm The demo version only permits to see the results of an example provided in the package.
New example: http://www.raczynski.com/pn/fluidsex1.htm
ORDER the full version of Fluids6
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Fluids5 users: Use the button below to upgrade to Fluids6. Please send us the date or the order number of your previous purchase of Fluids5.
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