Atmospheric Gusts

Abstract

Summary:— Starting with atmospheric motions on a global scale, different categories of atmospheric turbulence are discussed. It is pointed out that the turbulence within the earth’s boundary layer is comparatively better understood than any other type of turbulence, due to a concerted effort by meteorologists and by aircraft engineers. Clear air turbulence, turbulence in clouds and storms are subjects of active research, but we are still at the beginning of the understanding of these phenomena. The influence of atmospheric turbulence on some aspects of aircraft engineering is mentioned and the problem of the calculation or turbulence-induced loads is discussed in some detail. It is pointed out that the estimation of turbulence loads is a transposition of experience gained on one aircraft to another. The most simple technique of doing so is to assume that the atmospheric turbulence can be represented by a collection of single, isolated gusts and by making very simplifying assumptions about the dynamics of aircraft response. This technique, the discrete gust approach, in spite of serious theoretical reservations, has worked admirably well, but it appears that in many applications the limits of usefulness of the discrete gust approach have been reached. The alternative way of dealing with gusts is to treat them as a basically continuous phenomenon using the comparatively recently developed spectral technique. This technique not only permits the aircraft dynamics to be properly accounted for, but also describes the atmospheric turbulence in more realistic fashion, understandable not only to aircraft engineers but also to meteorologists and students of fluid dynamics.