Grid Fins are unconventional control surfaces, consisting of cells in an outer frame. Uniqueness of Grid Fins is that they are aligned parallel to the direction of air flow. The orientation of these fins results in aerodynamic demerits such as choking of flow inside the cells and thereby resulting in increased drag forces. Both experimental and Computational Fluid Dynamics (CFD) studies have been employed in negating these effects. This paper reviews the work done by various authors to overcome the anomalies using CFD approach. This paper also discusses the measures to overcome these anomalies. The paper presents an insight and step by step guidelines for CFD simulations right from the pre-processing to the post-processing.
The purpose of this paper is to initiate a 3-D non-spinning semi-circular missile model with a single generic planar fin and perform a computational analysis on it to understand the flow pattern around the fin. A freestream computational fluid dynamics analysis was done in the subsonic and supersonic Mach range, in which, the fluid behaviour was investigated using a two-equation turbulence model. A structured mesh was adopted to visualize the flow pattern around the fin. The aerodynamic coefficients were calculated for the model, and the predicted values were compared with the previous experimental results as well as the numerical results. This paper attempts to present all the possible flow visualizations which might help in better understanding of flow around missiles having planar fins. This work also attempts to establish a turbulent computational model for a single planar fin missile model for subsonic to supersonic range.
A flow field aerodynamic analysis using Computational Fluid Dynamics (CFD) model of a single wrap around fin is performed at 0° angle of attack and its flow visualizations are presented in this paper for a subsonic to supersonic Mach range. A comparative study is performed by utilizing two WAF geometries aligned in opposite directions and with different edges (Sharpened and Blunt). The aerodynamic characterization has been conducted using a realizable κ-ϵ turbulence model utilizing a high-quality mesh to understand the nuances of the flow around the curved fin structure. The quantities of interest are the computed aerodynamic coefficients which have been validated with their precursors. By investigating the contours of the pressure coefficient and the relative Mach number, the flow phenomenon in the vicinity of the curved fin can be understood in a finer way.
The experimental study (Schlieren photography) to characterize the flow behavior around a semi-cylindrical missile model having a single planar and wrap-around fin surface is performed inside a modified De-Laval nozzle test section capable of sustaining an airflow at Mach number ~1.7M. The images obtained from this schlieren technique is compared with flow field contour images of the similar missile models at similar flow conditions. The experiments are performed on a modified two-walled glassed section to assist the Schlieren imaging. The test section is calibrated preliminary to the experiments to assure the supersonic fluid flow. A comparison of flow images around the two types of fins further helps in characterizing the flow in their vicinity.
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