Integrating CFD and Experiment in Aerodynamics - CFD4Aircraft

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OPPORTUNITIES FOR THE INTEGRATED USE OF MEASUREMENTS AND COMPUTATIONS FOR THE UNDERSTANDING OF DELTA WING AERODYNAMICS I.A.Gursul Department of Mechanical Engineering, University of Bath, Bath, BA2 7AY, United Kingdom M.R.Allan and K.J.Badcock Computational Fluid Dynamics Laboratory, Department of Aerospace Engineering, University of Glasgow, Glasgow, G12 8QQ, United Kingdom Paper for the Conference on Integration of CFD and experiments at University of Glasgow, September, 2003 Abstract This paper considers the current status of delta wing research from the point of view of the potential for using joint experimental and computational studies to advance the subject. After a brief review of the available measurement and numerical methods, delta wing phenomena are considered in the following categories: shear layer instabilities, vortex breakdown, vortex interactions, nonslender vortices, multiple vortices, manoevring wing vortices and vortex/flexible wing interaction. It is concluded that CFD can be very valuable to guide the type amd location of experimental data collected and to enhance the understanding of the data but adding information. Currently CFD requires more datasets 1
2 which include boundary layer and field information and which ideally combine different types of data. 1 Introduction The flow over a delta wing at moderate angles of attack is dominated by two large, counter-rotating leading-edge vortices that are formed by the roll-up of vortex sheets. The flow separates from the leading edge of the wing to form a curved free shear layer above the suction side of the wing, which rolls up into a core. The time-averaged axial velocity is roughly axisymmetric and its maximum can be as large as four or five times the free stream velocity. These large axial velocities are due to very low pressures in the vortex core, which generate additional suction and lift force on the delta wings. A great deal of effort has been focused on the study of these vortices and aerodynamics of delta wings, as summarised in a review article by Lee and Ho [1]. The opportunities for gaining a deep understanding of the behaviour of the vortical flow has been greatly enhanced in recent years due to a revolution in the methods which can provide raw data. These methods can involve experiments using an expanding range of field and surface techniques or Computational Fluid Dynamics (CFD). It has been traditionally the case that these have been used with only very limited interaction, often only involving validation of the computational results using legacy experimental data which might not even be very suitable for the task. However, it is becoming increasingly recognised that if the goal is to improve the understanding of aerodynamics then these methods must be used in a deeper and coordinated way. The purpose of this paper is to give suggestions for how this statement can be realised for delta wings. 2 Tools Available for Aerodynamic Studies 2.1 Experimental Techniques There are several experimental techniques available for experimental research in delta wing aerodynamics: 1. Steady and unsteady pressure measurements including pressure sensitive paints. These are limited to wing surface measurements and so do not provide information on off-surface flow and the nature of the vortices.
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