Unsteady CFD Studies for Gust Modeling in Store Separation

Abstract

Aircraft and different store configurations must be certified before a flight. There is a small but finite probability of aircraft being hit by gust wind at the time of separation. Most store separation analyses from airborne platforms do not consider the gust phenomena because of the complexity and inadequate knowledge of its behavior. A dedicated task group was recently created to understand the gust-related phenomena in aircraft safety. Of the various gust cases, vertical gust is most severe and can cause instability leading to store collision. The situation is compounded in a long and heavy store due to its large projected area. No test procedures exist for simulation or practical tests of gust. A study was conducted to identify a test procedure for gust simulation using MIL standard data and Indian conditions. The current paper studies the emergency release condition where a vertical gust is hitting the aircraft to ascertain safe separation. A discrete gust with a 1-cosine shape and specified length and amplitude is imposed at the inflow boundary. The gust is allowed to sweep the computational domain containing the airborne platform and the store. The computed trajectory of the store, the miss distance, and its angular rates in the presence of gust are analysed in this work to study the safe separation of a store from an airborne platform. Simulations are also carried out to determine the effect of gust at the highest dynamic pressure in the flight envelope.