Vortex lattice method

About: Vortex lattice method is a research topic. Over the lifetime, 779 publications have been published within this topic receiving 9242 citations.

Aerodynamic and Aeroelastic Insights Using Eigenanalysis

Abstract: This paper presents novel analytical results for eigenvalues and eigevectors produced using discrete time aerodynamic and aeroelastic models. An unsteady, incompressible vortex lattice aerodynamic model is formulated in discrete time, the importance of several modeling parameters is examined. A detailed study is made of the behavior of the aerodynamic eigenvalues both in discrete and continuous time. The aerodynamic model is then incorporated into aeroelastic equations of motion. Eigenanalyses of the coupled equations produce stabililty results and modal characteristics which are valid for critical and non-critical velocities. Insight into the modeling and physics associated with aeroelastic system behavior is gained by examining both the eigenvalues and the eigenvectors. Potential pitfalls in discrete time model construction and analysis are examined.

A Framework for Constrained Control Allocation Using CFD-based Tabular Data

Abstract: This paper describes a framework for control allocation problem using Computational Fluid Dynamics (CFD) aerodata, which is represented by a multidimensional array of dimensionless coefficients of aerodynamic forces and moments, stored as a function of the state vector and control-surface deflections. The challenges addressed are, first, the control surface treatment for the automated generation of aerodata using CFD and, second, sampling and data fusion to allow the timely calculation of large data tables. In this framework, the generation of aerodynamic tables is described based on an efficient sampling/data fusion approach. Also, the treatment of aerodynamics of control surfaces is being addressed for three flow solvers: TORNADO, a vortex-lattice method, and two CFD codes, EDGE from the Swedis Defence Agency and PMB from the University of Liverpool. In TORNADO, the vortex points located at the trailing edge of the flaps are rotated around the hinge line to simulate the deflected surfaces. The transpiration boundary conditions approach is used for modeling moving flaps in EDGE, whereas, the surface deflection is achieved using mode shapes in PMB. The test cases used to illustrate the approaches is the Ranger 2000 fighter trainer and a reduced geometry description of Boeing 747-100. Data tables are then generated for the state vector and multiple control surface deflections. The look-up table aerodata are then used to resolve the control allocation problem under the constraint that each surface has an upper and lower limit of deflection angle.

Experimental investigation of linear and nonlinear aeroelastic behavior of a cropped delta wing with store in low subsonic flow

Abstract: The present paper aims to investigate flutter phenomenon for cropped delta wing with an external store using numerical and experimental methods in a subsonic and incompressible flight regime. Wing structure is modeled based on von Karman plate theory. The unsteady vortex lattice method is applied to wing aerodynamic model and a slender-body theory is used for store aerodynamic model. The experimental tests have been conducted in an incompressible subsonic wind tunnel. The comparison indicates a satisfactory agreement between the experimental results and the theoretical analyses. Moreover, the effects of different parameters such as wing thickness, wing aspect ratio, spanwise store position, store mass, the aerodynamics of the store, underwing clearance and store center of gravity on both flutter speed and instability boundary of the wing are studied both analytically and experimentally. Also, the system behaviors and the oscillation amplitude are examined experimentally for post-flutter where time history simulation and phase portrait are obtained for various velocities. The FFT analysis of time history measured data shows that beside the dominant harmonic frequency, both superharmonic and subharmonic frequencies are clearly identifiable. The results obtained from experimental bifurcation diagram indicate the presence of hysteresis loop regions corresponding to the stable LCOs.

Estimate of loads during wing-vortex interactions by Munk's transverse-flow method

Abstract: The inviscid, incompressible interaction of a wing with a vortex is studied by use of Munk's transverse-flow method. The method assumes that the loading on the wing is such that the local circulatory flow of the vortex is turned so that the wing and its vortex wake act as a barrier to the flow. This permits the analysis to be carried out by mapping the transverse flowfield into the flow about a circle to find the vorticity distribution in the wake. Closed-form expressions are then derived for the bound circulation in the wind and for the lift and rolling moment induced by the vortex on the encountering wing. Comparisons of the loads predicted by these relationships with those of vortex-lattice theory for a flat wing of a rectangular planform indicate that they accurately represent the various parameters when the aspect ratio of the encountering wing is less than about two. When flat rectangular wings of higher aspect ratios are considered, some sort of correction is needed. Examples are then presented to illustrate some applications of the results.