New enhancements, including adaptive timestep capabilities, improvements to the heat exchangers, graphs with new functionalities and a fresh new appearance as well as a host of other improvements have been added to Flownex Simulation Environment that enables you to design and optimize any system where fluid is the driving factor.

 

Adaptive Timestep

 

An adaptive timestep functionality has been added to the Flownex solver that automatically refines the timestep size through a transient simulation. This results in small timesteps when fast transients (such as pressure pulses during water hammer) are occurring to accurately predict the solution and larger timesteps when possible to effect shorter solving times..

Figure 1 FLownex 2019

Figure 1: Adaptive Time Step in Scheduler.

This feature monitors the pressure, energy, mass flow and density of all the components and will automatically reduce the timestep to ensure that the solution remains within the specified accuracy criteria. This allows the user to accurately predict fast transients such as pressure pulses without having to perform a temporal convergence study first.

 

Cavity Editor

 

One of the main capabilities of Flownex is to simulate turbomachinery flows.

The inputs of the Rotor-Rotor and Rotor-Stator components have been significantly enhanced in order to allow a user to easily specify a complex geometry for the cavity.

The complex geometry can be specified by using the Cavity Editor, which opens when double clicking on a Rotor-Rotor or Rotor-Stator component. The Cavity Editor allows the user to import a background picture for the cavity. The geometry and dimensions can then be defined on the picture in the Cavity Editor, as seen in Figure 2.

Figure 2 FLownex 2019

Figure 2: Rotor-Stator Cavity Editor – Reference Measurements.

After a picture has been imported, the user can define the dimensions of the cavity by specifying two points at any location on the drawing. Thereafter, the rotor and stator surface geometries are easily drawn on top of the picture.

Figure 3 FLownex 2019

Figure 3: Rotor-Stator Cavity Editor – Rotor Surface Geometry.

Other geometric items like the position of bolts, gap and shroud width, as well as defining the discretization is also done easily using this Cavity Editor.

Figure 4 FLownex 2019

Figure 4: Rotor-Stator Cavity Editor – Discretization.

 

Gibbs Free Energy Reactor

 

The combustion category has been renamed to Chemical Reactions. The existing Adiabatic Flame model is a chemical reaction where the end temperature and composition of the end product of the reaction is determined by the CEA calculations. Another component has been added to the Chemical Reactions library where the user can specify the end temperature of the chemical reaction, namely the Gibbs Free Energy Reactor.

Figure 5 FLownex 2019

Figure 5: Gibbs Free Energy Reactor.

The component uses the NASA CEA program to predict the reaction products at the specified end temperature. This component will then calculate the change in Gibbs free energy and enthalpy during the reaction. As part of this enhancement, a Gibbs free energy result has been added on all flow nodes. The first application of this reactor is to model fuel cells and use Flownex to optimise the surrounding systems. There are however many other possible applications.

 

Heat Exchanger Improvements

 

The Heat Exchanger components in Flownex has been updated. These components are now easier to use, and a few essential features have been added. The heat exchangers that has been updated is the Shell and Tube Heat Exchanger, Finned Tube Heat Exchanger and the Recuperator, which has been renamed to a Plate Heat Exchanger. The changes make using the heat exchangers for a general application like radiators etc. simpler.

Furthermore, fouling factors and fin efficiencies have been added to the heat exchangers where relevant. These can be used to model degradation over time and changes in the condition of the heat exchangers.

New icons have been added for the Shell and Tube heat exchanger and the names now clearly indicate the shell side and the tube side.

Figure 6 FLownex 2019

Figure 6: Shell & Tube Heat Exchanger.

Some input changes occur as far as Shell Side Primary Loss Calculations is concerned for Shell and Tube Heat Exchangers. The shell side supports specification of the friction factor through a constant value, using a script or using a Fanning friction chart. By default, the Fanning friction factor chart is used. The user can however easily use a correlation from another source in the script defined friction factor specification. These options can be seen in Figure 7.

Figure 7 FLownex 2019

Figure 7: Shell Side Primary Loss Options.

The shell side now supports built in correlations for the heat transfer coefficient calculation, as well as script defined heat transfer coefficient calculation, constant value specification and Stanton Prandtl charts. By default, the Shell Side heat transfer coefficient calculation correlation is used. The user can however easily use a correlation from another source in the script defined heat transfer coefficient calculation, as seen in Figure 8.

Figure 8 FLownex 2019

Figure 8: Shell Side Convection Coefficient Options.

The tube side supports specification of the friction factor through a constant value, Darcy Weisbach correlations, using a script or using a Fanning friction factor chart. By default, the Darcy Weisbach correlation is used.

The tube side supports built-in correlations for the heat transfer coefficient calculation, as well as script defined heat transfer coefficient calculation, constant value specification and Stanton Prandtl charts. By default, the Gnielinski correlation is used for the tube side heat transfer coefficient calculation.

Let’s see the few changes for Finned Tube Heat Exchanger. New icons have been added for the Finned Tube heat exchanger and the names now clearly indicate the fin side and the tube side.

Figure 9 FLownex 2019

Figure 9: Finned Tube Heat Exchanger.

A simplified set of inputs has been added to specify the geometry of a rectangular finned tube heat exchanger with round fins. This is the default option now, as seen in Figure 10.

Figure 10 FLownex 2019

Figure 10: Rectangular HX with Round Fins Inputs.

The user now specifies more readily available geometric parameters like the heat exchanger width height and length as well as tube and fin diameters. The older more generic specification is still available.

The fin side supports specification of the friction factor through a constant value, using a script or using a Fanning friction factor chart. By default, the Fanning friction chart is used. The user can however easily use a correlation from another source in the script defined friction factor specification.

The shell side now supports script defined heat transfer coefficient calculation, constant value specification and Stanton Prandtl charts. By default, Stanton Prandtl chart is used. The user can however easily use a correlation from another source in the script defined heat transfer coefficient calculation.

The tube side supports specification of the friction factor through a constant value, Darcy Weisbach correlations, using a script or using a Fanning friction factor chart. By default, the Darcy Weisbach correlation is used.

The tube side supports built-in correlations for the heat transfer coefficient calculation, as well as script defined heat transfer coefficient calculation, constant value specification and Stanton Prandtl charts. By default, the Gnielinski correlation is used for the tube side heat transfer coefficient calculation.

The Recuperator heat exchanger has been renamed to the Plate Heat Exchanger, which describes the functionality of the heat exchanger better. New icons have been added for this heat exchanger too.

Figure 11 FLownex 2019

Figure 11: Plate Heat Exchanger.

Both sides support specification of the friction factor through a constant value, Darcy Weisbach correlations, using a script or using a Fanning friction factor chart. By default, the Darcy Weisbach correlation is used with the addition of friction factor multipliers that can be used in the laminar and turbulent ranges to adjust the friction factor.

Both Primary and Secondary sides support built in correlations for the heat transfer coefficient calculation, as well as script defined heat transfer coefficient calculation, constant value specification and Stanton Prandtl charts. By default, the Gnielinski correlation is used for the tube side heat transfer coefficient calculation.

 

Graph Improvement

 

The appearance of the graphs in Flownex has been updated and the new graphs can be seen in Figure 12.

Figure 12 FLownex 2019

Figure 12: Comparison Between the Old and New Graphs in Flownex®.

The graphs inputs have been modified such that only basic graph properties are shown when creating a new graph to ease formatting/styling. Additional formatting properties are available when checking the Advanced Formatting properties, as seen in Figure 13.

Figure 13 FLownex 2019

Figure 13: Graph Properties.

New graph functionalities include:

  • By default, the Y-Axis will zoom and pan automatically for easy navigation.
  • The X-Axis will auto scale.
  • Line types can be changed to Step, Spline, Scatter Line, Area, Step Area or Spline area.
  • Line graph plotting data can be saved to a CSV file by simply right clicking on the graph.
  • A Crosshair cursor showing all Y-Axis values for a specific X-Axis value has been added.
  • Graphs formatting can be changed without having to solve the network again.

 

Custom Vortex

 

A Custom Vortex component has been added to the Rotating Components Library. The custom vortex is a vortex model commonly used in gas turbine cavity modelling. The tangential velocity is specified to produce a velocity profile between that of a forced vortex and free vortex. The radial velocity profile is specified in the following format. A custom vortex is characterised by a swirl constant, s, and a vortex weighing factor, n. The custom vortex model provides a simplified cavity model that allows the user to adjust the swirl constant and vortex weighing factor to match the swirl pressure rise seen in empirical measurements.

 

Liquid Gas Mixtures

 

The following components were extended to allow liquid-gas mixture fluid types, thereby allowing coupling of the secondary air system with the lubrication system: Rotating Channel, Rotating Nozzle, Nozzle, Rotor-Stator Cavity, Rotor-Rotor Cavity, Forced vortex and Free Vortex.

Rotating Components

 

The Daily and Nece correlation for calculating moment coefficients on disk surfaces was added as an option for the Rotor-Stator and Rotor-Rotor cavities.

In the case of the Rotor-Stator cavity, the Daily and Nece correlation allows for four different regimes, including fully interfering boundary layers within very small gap widths. The possibility to modify the Haaser et. al. correlation to be dependent on the gap width to disk diameter ratio was also added.

The Rotor-Stator and Rotor-Rotor cavities were upgraded to allow specifying an inner radius and outer radius for each disk individually, this is specifically useful when modelling cavities with axial inflows/outflows.
The Rotor-Stator and Rotor-Rotor cavities were upgraded to allow a disk surface profile specification that is not strictly rising with radius.

An option was added to all elements connected to vortices and cavities to specify the radius at the connection rather than the radius fraction. This allows the user to easily link the connection radius input to a measurement on a scaled drawing.

An increment result for windage power was added to the Rotor-Stator and Rotor-Rotor cavities. The windage power calculation of the Rotating Channel, Rotating Nozzle, Labyrinth Seal and Rotating Annular Gap was modified to automatically account for windage addition/removal to the element on account of upstream node swirl speeds not equal to that inside the element. Previously the windage power added to these elements was solely attributed to that required to maintain the swirl speed inside the element. This modification may lead to modified results since windage affects gas density.

The windage power calculation on the Forced Vortex component was modified to account for changes in kinetic energy of incoming flow streams that must increase/decrease in order to be equal to the swirl speed of the vortex at the particular connection radius. This modification may lead to modified results since windage affects gas density.

 

Some of the Minor Enhancements

 

The setup of measurements in scale drawings has been simplified. The user can now drag and drop properties from components onto measurement points and measurement lines.
If it is a measurement point, the user will be asked to which part of the coordinate (X,Y, or Z) it should be assigned. If the user drags and drops on a line, the property will automatically be associated with the length of the line.

The CFX interface is able now to handle both a point and a comma as decimal separator. Moreover, the option was added to deactivate the simulation when the CFX Generic Interface encounters an error. A user can continue the simulation from the point where the error (can include CFX solver crash) occurred, saving the time it took to reach that point.

The AFT importer has been improved to allow the import of scenarios that would not have the default Base names.

The Ansys mechanical link now allows a user to specify the name of boundary conditions to transfer load data. Specifying the same names for matching boundary conditions and named selections allows the user to use named selections in the link setup.

 

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