Study and Comparison of Aerodynamic Forces on an Aircraft and Suspension Bridge

Abstract

Aerodynamic forces are time varying forces experienced by objects undergoing air flow. The effect of these forces depends upon the shape and size of the objects. The aerodynamic force acting on a bluff body like bridge deck is different from that acting on a stream line body like an aircraft.This paper focus on the study and comparison of aerodynamic forces acting on an air craft and a bridge deck. I. INTRODUCTION Researches are booming in the area of aero-dynamics of civil structures, which are not usually designed to influence or accommodate the airflow over them, but rather with other objectives in view. The aero-dynamics of such structures is characterized by separated flow and turbulent wakes exhibiting widely varying degrees of flow organizations. A body immersed in a fluid flow is subjected to surface pressures induced by the flow. If the oncoming flow is turbulent, this will be one of the sources of time dependent surface pressure. If the body moves or deforms appreciably under the induced surface pressure, these deflections, changing as they do the boundary conditions of the flow, will affect the fluid forces, which in turn will influence the deflections. Aero- elasticity is the discipline concerned with the study of the phenomenon wherein aero-dynamic forces and structural motions interact significantly. If the body in the fluid flow deflects under some forces and the initial deflection gives rise to successive deflections of oscillatory and/or divergent character, aero-elastic instability is said to be produced. All aero-elastic instabilities involve aero-dynamic forces that act on the body as a consequence of its motion. Such forces are termed self-excited. A body is said to be aerodynamically bluff when it causes the wind flow around it to separate from its surface leaving a significant trailing wake. In contrast, wind flow around a streamlined body remains tangential and attached to its entire surface, leaving a narrow trailing wake. Most civil engineering structures, including the bridge sections of the long span bridges qualify as bluff bodies, while the shapes of an airfoil belong to the category of a streamlined body. The fundamental aspects of aero-elastic phenomena that need to be taken into account in the design of certain structural members, towers, stacks, tall buildings, suspension bridges, cable roofs piping system and power lines are not completely understood. Without aerodynamics airplanes cannot fly. Thus while considering performance of an aircraft it is no surprise that aerodynamics is a vital aspect. The philosophy of good aerodynamics is primarily derived from low drag. Aerodynamics is dynamics related with flow of air. It is classified into two external aerodynamics and internal aerodynamics. External aerodynamics deals with flow of air over a body. Internal aerodynamics deals with flow of air with in ducts.