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The Local Vorticity Content of a Shear Layer

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Separated and Vortical Flow in Aircraft Wing Aerodynamics

Abstract

In the mid 1980s computer speed and storage had developed to a degree that Euler methods (Model 8 in TableĀ 1.3) became a viable tool for aerodynamic design work. At that time very much discussed was the fact that at delta wings with sharp leading edges lee-sideĀ vortices resulted in the relevant angle of attack and Mach number regime. The question was, where is the apparent vorticity coming from, and accordingly the associated entropy rise.

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Notes

  1. 1.

    See also the introductory discussion in Sect.Ā 1.4.

  2. 2.

    Regarding the definition of the boundary-layer thickness see AppendixĀ A.5.4.

  3. 3.

    A discussion of the flow at the trailing edges of real airfoils and wings is given in Chap.Ā 6.

  4. 4.

    The amount of vorticity which must be canceled is small compared to the amount of vorticity of each of the involved boundary layers, usually only a few per cent.

  5. 5.

    These properties are important, because behind a straight shock wave with constant pre-shock Mach number, a total pressure lossĀ is present, but no vorticity. See in this regard Croccoā€™s theorem, Sect.Ā 3.5.

  6. 6.

    Note that a discrete (Model 8) Euler solution close to a solid surface always exhibits a thin total-pressure loss layer, casually called Euler boundaryĀ layer. That is an artifact due to the finite discretization of the computation domain and the flow variables used.

  7. 7.

    Note that the stream surface of the boundary layer does not lie in a plane, as in the two-dimensional case, Fig.Ā 4.3. Even more complex forms of the stream surface are possible [7].

  8. 8.

    See the examples in Chap.Ā 8.

  9. 9.

    The figure is based on a computation case in [14]. The flow field was computed with exact potential theory (Model 3 of TableĀ 1.3) [15, 16].

  10. 10.

    Trailing edge properties as well as the Kutta condition in reality are treated in Chap.Ā 6.

  11. 11.

    LighthillĀ calls the trailing vorticity also residual vorticity.

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Hirschel, E.H., Rizzi, A., Breitsamter, C., Staudacher, W. (2021). The Local Vorticity Content of a Shear Layer. In: Separated and Vortical Flow in Aircraft Wing Aerodynamics. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-662-61328-3_4

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  • DOI: https://doi.org/10.1007/978-3-662-61328-3_4

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