Type 8 analyses

Updated May 17, 2021

------------------ WORK IN PROGRESS ------------------



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Description

Purpose

Type 8 analyses have been introduced in flow5 v7.13 to enable the fast calculation of operating points for any combination of angle of attack, sideslip and freestream velocity. This has been made possible by the option also introduced in v7.13 to make bettter use of the problem's linearity to calculate the solutions to the type 1, 2, 3, 5 or 7 analyses.

The type 8 analysis is very similar in principle to the type 1 and type 5 analyses, with the addition that the stability derivatives are generated for each operating point, whether or not the pitching moment is zero, and whether or not the sideslip is zero. The significance and validity of the stability derivatives in non-stable flight conditions should be considered with caution, especially considering the high variablity of these derivatives with the angle of attack.

Limitations

  1. Similarly to the type 1, 2, 3, 5 and 7 analyses, one important limitation of the type 8 analysis is that the wake is defined as a a fixed set of flat panels extending downstream from the trailing edges and aligned with the x-axis. This may cause numerical interactions of wake and body panels.
  2. Only fixed speed analyses are enabled, i.e. there is no option as of v7.13 to adjust automatically the speed to compensate the weight.
  3. The control derivatives are not evaluated as part of the calculation. The reason for this limitation is that these derivatives cannot be evaluated using linear combinations of the unit results.




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Validation

It has been checked that the type 8 analyses produce the same results as a type 1, 5 or 7 analysis if the angle of attack, sideslip angle and freestream velocity are the same.
This validation can be performed on any test case, and it can be a useful step to perform anyway to check that the analyses are defined as intended by the user.




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Step by step

The analysis is selected by activating the option in the analysis editor.


The operating point is defined by the values of the angle of attack, of the sideslip angle and of the freestream velocity specified in the top right widget.



As of v7.13, the operating points are identified in the tree explorer by a name in the format "α°_β°_V∞".


Since the operating points do not necessarily assemble in a smooth curve, an option has been added to plot the polar's curves as symbols only.

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