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Grid fins are unconventional control and lifting surfaces consisting of an outer frame supporting an inner grid of small chord intersecting planar surfaces. Credited for their enhanced lifting characteristics at high angles of attack and wider Mach number regimes, minuscule hinge moments, and increased drag, these have been used in numerous aerospace applications. Removal of their cross-members leads to its simplified variant called cascade fins. The present study carries out numerous viscous computational fluid dynamics simulations at subsonic speed and high angles of attack to investigate and compare the impact of the horizontal planar member cross-sectional shape on cascade fin aerodynamics by elucidating the effects of using a NACA 0012 airfoil cross-section instead of a rectangular cross-section and varying the gap between their members. Appreciably higher aerodynamic efficiency attributed to drag reduction and comparable lifting characteristics along with steeper and hastened stall characteristics was deciphered for airfoil cascades. It was also found that optimally reducing the gap alleviates the stall tendency. These trends were further explained using pressure distribution plots and flow visualization analysis for the respective variant. Thus, planar member cross-section and gap selection should be done based on the aerodynamic efficiency requirement, desired maneuverability, and manufacturing cost. [ABSTRACT FROM AUTHOR]

A numerical study of two microramp geometries has been conducted to study their effectiveness in controlling swept shock wave-boundary-layer interactions. The planar shock wave is generated by placing a 20 deg sharp fin in a supersonic flow at Mach 4. The heights of microramps were varied as 30,40,50,60,70, and 90% of the boundary-layer thickness. The effect of microramp width and spacing is also studied. It is observed that boundary-layer separation is delayed significantly, downstream of the devices. Further, larger ramp heights were found to be more beneficial in delaying the separation. [ABSTRACT FROM AUTHOR]

The article focuses on a study which described the use of Kirchhoff's steady-state stall model for the modeling of nonlinear longitudinal aerodynamics linked to single/cascade fin models at high angles of attack. Geometric models for the flat plate (FP) and airfoil (AF) along with the parameters of the models as length, chord and thickness of the planar fin are shown. The equation used to calculate the steady-state flow separation point based on Kirchhoff's theory of flow separation is given.

Parameter estimation of cascaded fins at high angle of attack is carried out using a new neural-network approach. Two new lift models are proposed to overcome the problems faced by high angle-of-attack lift models based on Kirchhoff's theory of flow separation. Lift modeling is carried out using a neural network for single and cascaded planar fins of airfoil and rectangular cross sections. Neural partial differentiation is applied to find the lift curve slope at zero angle of attack, which is more consistent compared to that based on average slope obtained using output-error method. Neural approach is applied to model the steady flow separation point on the fin. Separation and stall characteristic parameters are estimated using a new neural formulation. It is shown that the values of these parameters, obtained using the proposed neural method, better represent the observed lift data compared to those from the output-error method. Moreover, a modified equation is suggested to better model the steady separation point for the cascaded fins. It is shown that the new equation for the separation point, when used in conjunction with the new lift coefficient equation, produces lift coefficient values which better match the measured ones. It is also shown that for an optimum gap-to-chord ratio the separation parameter will be maximum implying a delayed stall. Further, it is shown that an increase in the number of fins in the cascade has the effect of increasing the stall angle in addition to the increase in lift curve slope. [ABSTRACT FROM AUTHOR]