Azar Eslam Panah

Vorticity Generation and Transport on a Plunging Wing

Two-component particle image velocimetry and surface pressure measurements are used to characterize the flow field over a plunging nominally two-dimensional flat-plate airfoil at zero geometric angle of attack, and a finite wing with rectangular planform and a semiaspect-ratio sAR = 2. Phase-averaged horizontal and vertical planes of PIV data are used to reconstruct a three-dimensional volume in which the evolution of the vortex structure is rendered, and vorticity transport is quantified within a chordwise planar control volume bounded by the flat plate surface, and containing the leading-edge vortex. It is shown that, for the two-dimensional airfoil, generation of secondary vorticity of opposite sign to the leading-edge vortex occurs at a rate of approximately half that of the leading-edge shear layer flux, suggesting that entrainment of this vorticity into the leading-edge vortex has a significant impact on the strength of the vortex. Also, spanwise convection of vorticity has a non-negligible impact on control-volume circulation during the second half of the stroke. In the case of the finite wing, the initial development of the leading-edge vortex is qualitatively similar to that of the nominally two-dimensional case; however, through the mid-portion of the stroke, the leading-edge vortex rapidly evolves into an arch structure as it convects along the chord, as seen in previous studies. In contrast to the case of the nominally two-dimensional airfoil, spanwise flow acts to significantly deplete the circulation within the leading-edge vortex. The difference between control-volume circulation and the sum of the integrated convective boundary fluxes suggests that the fraction of the total vorticity flux supplied by the finite wing surface beneath the leading-edge vortex is similar to that of the two-dimensional case.

Vortex Shedding and Wake Structure of a Plunging Wing

The structure and dynamics of leading-edge and trailing-edge vortices (LEV and TEV) are investigated for a plunging flat plate airfoil at a chord Reynolds number of 10,000 while varying plunge amplitude and Strouhal number. Digital particle image velocimetry measurements are used to characterize the shedding patterns and interactions of the LEV and TEV. A classification scheme is established to describe the qualitative structure of the wake, which is shown to be dependent primarily on Strouhal number. However, convection of the LEV in the chordwise direction, and its resulting interaction with the TEV is also strongly influenced by plunge amplitude. The development of the leading-edge and trailingedge vortices is tracked using phase-locked measurements throughout the cycle and the circulations of the LEV and TEV structures are measured. A scaling parameter proposed by Buchholz, Green, and Smits 20 for the circulation shed by a pitching panel reduces the variability of the circulation measurements but is found to be lacking physics relevant to the present problem. A modified parameter, taking into account the effect of free-stream velocity, is proposed, which provides an improved scaling of the circulation data.

Scaling of Circulation Shed by an Oscillating Airfoil

The kinematics of vorticity shed by a nominally two-dimensional plunging at-plate airfoil are investigated for varying Strouhal number, heave amplitude, and angle of attack. The structure of leading-edge and trailing-edge vortices (LEVs and TEVs) is described with variation of these parameters. The circulations of the LEVs and TEVs are computed, and a previously-developed scaling is applied to these values. Although the circulation values exhibit a high degree of similarity before scaling, the parameter is found to further reduce the variability of the LEVs.

Unified evaluation of total radiation in urban environments

ABSTRACT The increasing complexity of modern architectural geometries emphasizes the need for more accurate simplified calculations of comfort analysis in architectural design. In most applications, the designer roughly estimates several parameters involved in thermal comfort that are very difficult to compute, among which the components of Mean Radiant Temperature (MRT) are notable. The goal of this paper is to propose a fast reliable technique, named Numerous Vectors (NV), to calculate MRT even in the presence of complex geometries. Considering the area, orientation, and distance of different radiant geometries, the process suggests an innovative method to find geometric-related parameters such as view factors by projecting the surrounding surfaces on a unit sphere representing the human body. The NV method is much faster than conventional methods. Moreover, all the geometry-related components of MRT including the radiation of individual surfaces, solar radiation, and the atmospheric radiation are calculated in one single step. The results are proved to be in a good agreement with analytical data.