The role of horizontal rolls in rapid intensification of cyclonic vortex

<p>The present laboratory study is focused on the role of convective rolls in enhancement of the heat flux from the sea and triggering of the process of rapid intensification of tropical cyclones. The appearance of coherent convective structures such as thermals and rolls are registered by different optical techniques and temperature measurements. Two-dimensional velocity fields are used for the study of the structure and characteristics of the flow. The heat flux from the heating plate to the fluid is measured directly. Obtained results clearly show that rapid intensification of a laboratory analog of a tropical cyclone is tightly linked with the heat transfer process in the boundary layer. Formation of secondary convective structures strongly increases the heat transfer and intensity of convective circulation. Intensity of radial inflow is a crucial aspect for the intensification of cyclonic vortex, hence rapid variation of the heat transfer is a factor that has a substantial influence on the dynamics of a laboratory vortex. </p>

In situ analysis of shear bands and boundary layer formation in metals

Shear banding is a plastic instability in large deformation of solids where the flow becomes concentrated in narrow layers, with broad implications in materials processing applications and dynamic failure of metals. Given the extremely small length and time scales involved, several challenges persist in studying the development of shear bands. Here, we present a new approach to study shear bands at low speeds using low melting point alloys. We use in situ imaging to directly capture the essential features of shear banding, including transition from homogeneous to shear banded flow, band nucleation and propagation dynamics, and temporal evolution of the flow around a developing band. High-resolution, time-resolved measurements of the local displacement and velocity profiles during shear band growth are presented. The experiments are complemented by an analysis of the shear band growth as a Bingham fluid flow. It is shown that shear banding occurs only beyond a critical shear stress and is accompanied by a sharp drop in the viscosity by several orders of magnitude, analogous to the yielding transition in yield-stress fluids. Likewise, the displacement field around a nucleated band evolves in a manner that resembles boundary layer formation, with the band thickness scaling with time as a power law.

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.

Attenuation of Sounds in a Pipe with Shear Flow Using Layered Metamaterials

This study presents a simulation of interactions between sound and a surrounding pipe structure conveying fluid flows. A sound-attenuating structure using layered metamaterials of cylindrical shells is proposed and verified. Numerical simulations based on the finite difference method after considering steady fluid flow in the pipe were performed. The effective wave speed and density of the fluid required to determine acoustic characteristics were calculated from the transfer matrix method. This enabled estimation of noise reduction capability. The metastructure layers were lined parallel to the pipe walls to minimize flow resistance. The effective density was negative near the resonance frequency of the layers. The transmission loss predicted for a moving fluid medium was smaller than that for a stationary medium due to boundary layer formation. The proposed method can be used to design silencers to reduce the transmitted noise in pipe systems.