Numerical
investigations of unsteady interaction of
turbomachinary blades V.M.Lapotko, Yu.P.Kukhtin Ivchenko "Progress" Design Burea Ivanova, 2, Zaporozhye, 69068, Ukraine The observed tendency of the axial
turbomachinery development being featured by increasing of rotor rpm,
decreasing of axial distance between separate disk rims, using of high-loaded
vane and blade cascades, requires importunately to develop, and apply in the
practice of R&D activities, unsteady flow calculation methods. The flow
non-stationarity being examined in this paper is caused by presence of relative
motion of the vane and blade cascade rigid surfaces. The well-known approach
based on using different coordinate systems - absolute one for vane cascades
and relative one for blade cascades - does not provide an acceptable accuracy
of calculation because of "spreading" of the flow parameters (environment
temperature, entropy and so on) at the cascade glide lines in the axial
clearance. The authors of this paper have developed and repeatedly evaluated on
different flow types a method of tracking flow streams (MTFS) fit for calculating the flow of
bodies with movable, unbounded, rigid surfaces. Using of this method allows to
perform simulation of unsteady flow of the relaxing gas in turbomachinery units
in single coordinate system (for example, in absolute one) which eliminates the
negative effect arising because of the grid gliding. The method of tracking
flow streams is based on using movable, so called Lagrangian grids. These are
infinitesimally thin, weightless and impenetrable to main flow surfaces. The
permeability of surfaces of such kind is allowable only for moles of the medium
simulating the diffusion caused by the medium physical viscosity and turbulent
flow. A universal calculation algorithm developed by the authors provides both
the coincidence of these surfaces with the flow streams interfaces and the satisfiability
of the laws of conservation of mass, momentum and energy for each element of
calculation area. The introduction of such approach in the practice of
designing turbomachinery units in SE Ivchenko Progress ZMKB allowed to solve a
number of technical tasks with acceptable accuracy, including an estimation of
aerodynamic action of upstream and downstream guide vane rims and struts of
exhaust systems on the rotor wheel blades, for optimization of the axial
clearance. As a technical-and-scientific process stock carried out were
numerical investigations on estimation of the clocking effect as applied to
turbine blade cascades, as well as investigations of the unsteady flows in the
disk rims of the counter-rotating turbomachinery units. So: the results of
calculating the unsteady
interaction of the counter-rotating propfan cascades have shown that the
approach described above is fit for simulating unsteady gas flows in turbomachinery units under conditions close
to real ones. With such approach no negative grid effects occur, associated
with gliding of the grids and leading to loss of accuracy. After corresponding
verification the calculation program developed can be used for carrying out an
optimization of turbomachinery units stages. |
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