MHD-shock structures of astrospheres: λ Cephei -like astrospheres

ABSTRACT The interpretation of recent observations of bow shocks around O-stars and the creation of corresponding models require a detailed understanding of the associated (magneto-)hydrodynamic structures. We base our study on 3D numerical (magneto-)hydrodynamical models, which are analysed using the dynamically relevant parameters, in particular, the (magneto)sonic Mach numbers. The analytic Rankine–Hugoniot relation for HD and MHD are compared with those obtained by the numerical model. In that context, we also show that the only distance which can be approximately determined is that of the termination shock, if it is an HD shock. For MHD shocks, the stagnation point does not, in general, lie on the inflow line, which is the line parallel to the inflow vector and passing through the star. Thus an estimate via the Bernoulli equation as in the HD case is, in general, not possible. We also show that in O-star astrospheres, distinct regions exist in which the fast, slow, Alfvénic, and sonic Mach numbers become lower than one, implying subslow magnetosonic as well as subfast and subsonic flows. Nevertheless, the analytic MHD Rankine–Hugoniot relations can be used for further studies of turbulence and cosmic ray modulation.

CFD Analysis of Controlling the Airflow over Airfoils using Dimples: Technical Note

The main objective of this work is to improve the aerodynamic characteristics and manoeuvrability of the aircraft. The reduction in drag and stall phenomena will automatically enhance the aerodynamic characteristics. This project is an effort to enhance the aerodynamic characteristics of airfoil by introducing surface modifications in the form of dimples. The shape of the dimples we selected is circular shaped dimple. We placed 12 dimples in both the surfaces in appropriate places so that they could delay the boundary layer formation. The dimple generally creates turbulence by creating vortices which in turn delays the boundary layer formation. With the effects of dimple, pressure drag gets reduced and also the acoustic effects get reduced. This project includes the computational analysis of dimple effect on aircraft wing using NACA 0018 symmetric airfoil with uniform cross section throughout the length of airfoil. Subsonic flows are considered for this analysis. The analyses were done under the inlet velocities of 30m/s and 60m/s at different angle of attack such as 0, 5, 10 and 15 degrees. The models were designed using CATIA V5 and simulated using ANSYS CFX software.

Dynamics of viscoelastic element of flow channel

We consider the plane problem of aerohydroelasticity on small oscillations arising during bilateral flow around a viscoelastic element located on the rectilinear wall of an infinite channel. A mathematical model describing the problem in a linear formulation and corresponding to small perturbations of homogeneous subsonic flows and small deflections of a viscoelastic element is formulated. Using the methods of the theory of functions of a complex variable, the solution of the problem is reduced to the study of the integro-differential equation with partial derivatives with respect to the deflection function of the element. To solve this equation, a numerical method based on the application of the Bubnov-Galerkin method is proposed, followed by the reduction of the resulting system of integro-differential equations to the Volterra vector equation of the second kind. On the basis of the developed numerical method the computer simulation of the dynamics of the deformable element is carried out.

CFD Analysis of Aircraft Curved C-D Nozzle: Technical Note

A nozzle for the aircraft can be designed by considering the exit Mach number. In order to get a premeditated Mach number, we need to convert pressure energy into kinetic energy by using a nozzle. Convergent nozzles are utilized for subsonic flows while Convergent-Divergent (C-D) nozzle is utilized for supersonic flows. Curved nozzle flow is accelerated from low subsonic to sonic velocity at the throat and further expanded to supersonic velocities at the exit, in a C-D nozzle. This paper details the relevancies on designing a curved nozzle to attain super-sonic flow and maximizing the optimal thrust and devoid of flow separation due to shock waves. The navigation of the flow must be parallel to the axis of the nozzle for achieving extreme thrust and proficiency. Based on the fundamental gas dynamic equations, this study aims to develop a theoretical approach for the calculation of the flow properties along the axis of the C-D Nozzle. The flow conditions were selected in consideration of the pressure, temperature and gases accessible at the exit of the combustion chamber.