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    Wyświetlanie 1-2 z 2
    Tytuł:
    Effects of turbulence induced by micro vortex generators on shockwave : boundary layer interactions
    Autorzy:
    Sznajder, J.
    Kwiatkowski, T.
    Powiązania:
    https://bibliotekanauki.pl/articles/245222.pdf
    Data publikacji:
    2015
    Wydawca:
    Instytut Techniczny Wojsk Lotniczych
    Tematy:
    transonic flow control
    laminar-turbulent transition
    vortex generators
    flow simulations
    BAY method
    Opis:
    Interactions between viscous and transonic effects in air flow around a laminar wing were investigated computationally by means of the solution of unsteady Reynolds-averaged Navier-Stokes Equations. The subject is important from the point of view of applications of Natural Laminar Flow technology in modern, economically efficient passenger aircraft. The research was focused on simulations and analyses of influence of turbulence induced by micro vortex generators on intensity of harmful transonic phenomena like strong shock waves and buffet. Two ways of modelling of the effects of turbulators – the micro vortex generators were taken into consideration. The first way consisted in resolving the shape and inclination angle of the generator in the grid over airfoil and setting the non-slip wall boundary condition on the surface of the generator. The second way, taking advantage of the BAY model of vortex generator, was implemented on orthogonal grid without the need of resolving the shape of the vortex generator in the grid. Calibration of the BAY model was aimed at producing similar distribution of vorticity and velocity circulation behind the model of the vortex generator, as obtained for the grid-resolved model of the vortex generator. The calibration procedure resulted, however, in overestimated turbulisation of the boundary layer in the BAY model, compared to the effects of the grid-resolved vortex generator. The flow simulations indicated, however, that turbulisation of boundary layer induced by micro vortex generators can reduce or eliminate the oscillation of strong shock wave and buffet in off-design conditions and that further adjusting of the BAY model is an efficient strategy for modelling the interactions between viscous and transonic effects in air flow around a laminar wing.
    Źródło:
    Journal of KONES; 2015, 22, 2; 241-248
    1231-4005
    2354-0133
    Pojawia się w:
    Journal of KONES
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Study on the effect of the descent rate of a helicopter in the Vortex Ring conditions
    Autorzy:
    Surmacz, K.
    Kowaleczko, G.
    Powiązania:
    https://bibliotekanauki.pl/articles/248016.pdf
    Data publikacji:
    2016
    Wydawca:
    Instytut Techniczny Wojsk Lotniczych
    Tematy:
    Vortex Ring State
    helicopter descent
    computational fluid dynamics
    flow simulations
    Opis:
    One of the limiting factors for a helicopter operation is the Vortex Ring State (VRS). This aerodynamic phenomenon, known as the VRS or “Settling with Power”, is characterized by the formation of circulating air stream moving along a ring shaped track around the main rotor of a helicopter. Conditions, conducive to development of the vortex ring state, occur in the vertical or nearly vertical descent. This leads to decrease in thrust and thus rapidly increasing the rate of descent. This phenomenon occurs for an appropriate combination of induced velocity and the velocity of the stream of airflow from the bottom to the rotor. The rates of change of velocities delimit dangerous areas of flight. The objective of this work was to investigate the influence of the descent rate of a helicopter on the vortex ring formation process and determinants of the occurrence of vortex rings. For better understanding of the nature of this state, a computational method was applied. Series of three-dimensional (3D) unsteady analysis was carried out using Computational Fluid Dynamics tools (CFD). Simulations were realized using geometry and performance of the W-3 “Sokol” helicopter. The paper presents results of a helicopter operation in axial and non-axial descent conditions. Three calculation cases of vertical flight of a helicopter with different rates of velocity changes were considered. A simulation of non-axial descent was based on the measured flight test data for the W-3 helicopter. The results provide information about the changing nature of the flow in the course of the movement of a helicopter and show the influence of the rate of descent during initiation on the development of VRS. Results of the calculations provide guidelines for helicopter pilots.
    Źródło:
    Journal of KONES; 2016, 23, 1; 345-352
    1231-4005
    2354-0133
    Pojawia się w:
    Journal of KONES
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-2 z 2

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