Integral Surface Analysis of Vortical Lobed NozzleFlows

Abstract

In many industrial and aerodynamical applications the mixing of flows is an essential part of the processes or work principles. In particular, mixing of the hot engine exhaust flow with the colder bypass air stream is a research topic in military aircraft design. Besides other concepts lobed nozzles are often applied in order to increase the mixing of hot and cold air and, thereby, to enforce the decreasing of the exhaust jet core temperatures lowering the infrared signature of the flight vehicle. In the present study the flow field generated by generic lobed nozzles is considered. Focal points of this work are generated vortical flow structures and their complex interaction in dependence of geometry variations of the lobes. Especially, the spreading of the vortices and the behaviour of the core part is examined in regard to the objective to derive order parameters which might be useful for the design of better mixing devices. This study is based on numerical flow simulations using a standard finite volume flow solver. Incompressible laminar flows at low Reynolds numbers are simulated addressing the fundamental physical mechanisms of vortex interaction, destructive shearing flows and vortex reorganisation and reconnection in the wake field of lobed nozzles. This work concentrates on the analysis of given numerical flow simulation results and it mainly addresses the benefits of flow field investigation by using integral surfaces of primitive and derived vector fields. The interaction of stream dividing velocity and vorticity integral surfaces is investigated. Enforced topological structure change and related diffusion processes are revealed by the topology of vortex sheets. Cutting the integral surfaces helps to elucidate special flow situations at distinct flow regions.