Electric vertical take-off and landing (eVTOL) aircraft with multiple lifting rotors or prop-rotors have received significant attention in recent years due to their great potential for next-generation urban air mobility (UAM). Numerical models have been developed and validated as predictive tools to analyze rotor aerodynamics and wake dynamics. Among various numerical approaches, the vortex method is one of the most suitable because it can provide accurate solutions with an affordable computational cost and can represent vorticity fields downstream without numerical dissipation error. This paper presents a brief review of the progress of vortex methods, along with their principles, advantages, and shortcomings. Applications of the vortex methods for modeling the rotor aerodynamics and wake dynamics are also described. However, the vortex methods suffer from the problem that it cannot deal with the nonlinear aerodynamic characteristics associated with the viscous effects and the flow behaviors in the post-stall regime. To overcome the intrinsic drawbacks of the vortex methods, recent progress in a numerical method proposed by the authors is introduced, and model validation against experimental data is discussed in detail. The validation works show that nonlinear vortex lattice method (NVLM) coupled with vortex particle method (VPM) can predict the unsteady aerodynamic forces and complex evolution of the rotor wake.

The steam consumption in a turbine within an operating pressure range determines the effectiveness of thermal energy conversion to electric power generation in a turbo-alternator. The low pressure (LP) stage of the steam turbine produces largest amount of steam to shaft-power in comparison to other stages of turbine although susceptible to various additional losses due to condensation of wet steam near penultimate and ultimate stages. The surface deposition in blade is caused by inertial impaction and turbulent-diffusion. With increasing blade stagger angle along the larger diameter of blading, the fractional deposition of wet steam is largely influenced by blade shape. From this background, the aim of this work is to predict the effect of mathematical models through computational fluid dynamics analysis on the characterization of thermodynamic and mechanical loss components based on unsaturated vapor water droplet size and pressure zones in LP stages of steam turbine and to investigate the influence of droplet size and rotor blade profile on cumulative energy losses due to condensation and provide an indication about the possible conceptual optimization of blade profile design to minimize moisture-induced energy losses.

SUMMARYThis paper deals with a two-dimensional train of free, internal gravity standing waves in an inviscid, incompressible, stably-stratified fluid bounded by a rigid base and free surface. The waves are similar to those studied by R. R. Long, and are assumed to be periodic in the horizontal direction, and independent of time. The classical linearized theory has been extended by examining the wave equation with a variable Lo2 parameter. The equation has been solved numerically, and the method of approach has been to regard the non-linear terms as ' perturbations ' on the main wave term which is treated in the classical linearized theory.Deviations from the linearized theory are shown to become more pronounced the larger the amplitude of the wave, as the streamlines become displaced by presence of the non-linear terms, and the relative magnitudes of non-linear coefficients are compared with the main terms for the cases computed. The undisturbed fluid stream is the same for all the computed wave profiles, and the amplitude has been varied from small to large to show the development of rotor regions.

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SUMMARYBy means of a transformation originally proposed by Long (1953) we obtain exact solutions for periodic wdve flow of a stratified shearing fluid between rigid plane boundaries. The examples worked out are less particular than any previously published, and show a substantial decrease in wavelength when the amplitude increases once rotors have been formed even though the equations are linear.