National Wind Tunnel Facility Research Articles

National Wind Tunnel Facility

National Wind Tunnel Facility

Nonlinear Modeling of Cascade Fin Aerodynamics Using Kirchhoff's Steady-State Stall Model

U NDER stationary attached flow conditions, aerodynamic effects can be adequately described using time-invariant parameters and linear models, but the models are highly nonlinear due to dominant unsteady effects and flow separation [1,2] at higher angles of attack. The models based on computational fluid dynamic methods, wind-tunnel (WT) tests, and semiempirical formulations provide a basis for analytical investigations of the complex flow phenomena, but postulating them in an analytical form suitable for parameter estimation is difficult. An alternative approach [3,4] has been followed to describe the flow separation analytically as a function of an internal state variable in the present study. The grid fins, sometimes also called the lattice fins, are a relatively recent development in guided missile technology [5], although grid fins exhibit more effective stability and control characteristics at intermediate and large angles of attack [6,7], but their aerodynamic efficiency is quite low.Misra [8] proposed a new category of grid fins (nomenclatured as “cascade fins”) with higher aerodynamic efficiency. A cascade fin has planar members (fins) placed parallel to each other at a distance based on an optimized gap-to-chord (g=c) ratio. It is the absence of crossmembers that makes a cascade fin different from a grid fin. This Note presents the modeling of nonlinear longitudinal aerodynamics associated with single/cascade fin models [8] at high angles of attack using Kirchhoff’s steady-state stall model. The WT data pertaining to single/cascade finmodels were used to analyze the effect of endplates, the number of planar fins in the cascade, and the g=c ratio on the stall characteristics parameters during nonlinear modeling and estimation. The National Wind Tunnel Facility [8] available in the Department of Aerospace Engineering at the Indian Institute of Technology, Kanpur, was used to generate the data consisting of the variation of lift coefficient (CL) as a function of angle of attack ( ).

Parameter Estimation from Flight Data of Hansa-3 Aircraft Using Quasi-Steady Stall Modeling

Nonlinear longitudinal aerodynamics of planar fins and aircraft at high angles of attack near stall have been modeled using Kirchhoff’s formulation. Both the steady-stall and quasi-steady stall models have been applied on the longitudinal aerodynamic data at high angles of attack pertaining to planar fins and Hansa-3 aircraft, respectively. The National Wind Tunnel Facility (NWTF) in the department of Aerospace Engineering at the Indian Institute of Technology, Kanpur was used to generate the wind tunnel data for planar fins with rectangular and NACA-0012 airfoil cross-sections whereas flight test data near stall for Hansa-3 aircraft were generated by executing a quasi-steady stall maneuver (QSSM). The Kirchhoff’s steady-state stall model was applied to wind tunnel data for modeling the flow-separation point and to estimate the parameters characterizing stall. The Kirchhoff’s quasi-steady stall model was applied to the compatible real flight test data to model the nonlinear longitudinal aerodynamics and estimate the aerodynamic parameters. An approach of fixing the parameters to their reasonably accurate values was followed during the estimation of quasi-steady stall characteristics and the longitudinal aerodynamic parameters using the maximum likelihood (ML) method from the nonlinear flight data pertaining to QSSM. The results obtained using both models were found to be encouraging and are presented in graphical as well as in tabular form. The estimated parameters using both models have been compared with the reference results. A well-matched comparison of the model’s estimated and real flight data hysteresis loop is also presented.

Modelling of Cascade Fin Aerodynamics Near Stall using Kirchhoff's Steady-state Stall Model

Nonlinear longitudinal aerodynamics associated with cascade fins at high angles of attack near stall has been modelled using Kirchhoff's formulation. Grid fins are a relatively recent development in guided missile technology. In this paper, a new category of grid fins, nomenclatured as cascade fins, has been proposed. In cascade fin design, an appropriate selection of gap-to-chord ratio and the number of planar members lead to desired stall angle and acceptable overall lift coefficient, respectively. Kirchhoff's steady-state stall model has been validated on wind tunnel data generated for Cascade fins having rectangular airfoil cross-section. National Wind Tunnel Facility (NWTF) of IIT, Kanpur, was used to generate the wind tunnel data consisting of the variation of lift coefficient with angle of attack. The cascade fins were tested to generate the data by varying gap-to-chord ratio and number of planar fins. The cascade fins with rectangular cross-section were tested with and without end plates. Kirchhoff's steady-state stall model was applied to wind tunnel data of cascade fins for modelling flow separation point and maximum likelihood method was used to estimate the parameters characterising stall characteristics. The effects of end plates, variation of number of fins and gap-to-chord ratio on parameter estimation were also studied. It has been observed that Kirchhoff's steady-state stall model could advantageously be applied to model nonlinear aerodynamics associated with cascade fins at high angle of attack. Defence Science Journal, 2011, 61(2), pp.157-164 , DOI:http://dx.doi.org/10.14429/dsj.61.481

Low-speed Closed Circuit Wind Tunnel, Kanpur, India

The National Wind Tunnel Facility project (NWTF) is a sophisticated precision built, 150 m long, low-speed, closed circuit wind tunnel and has a test section of 3 × 2.25 × 8.75 m. The tunnel is designed for maximum air speed of 90 m/s. The NWTF has been constructed to meet national need in the areas of aeronautical and nonaeronautical research and development work. It provides a wide range of facilities such as industrial aeronautical and wind engineering applications for bridges, towers, antennas, chimneys, tall buildings and testing of ground vehicles. This project is the largest closed circuit Reinforced Cement Concrete (RCC) Wind Tunnel in India.