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.

Longitudinal stability and motion of trimaran wing in ground effect model during take-off

Abstract: Wing in Ground Effect is a relatively new concept in transportation technology. It is more efficient than conventional aircraft and quicker compared to conventional marine vehicles. However WIG is still not widely use as a public transportation. One of the criteria to be fulfilled is stability. Longitudinal stability of WIG craft is still of concern to the designer and the solutions are being investigated. Instability of a small WIG craft occurs when aerodynamic-hydrodynamic phase changes into pure aerodynamic phase during the take-off. In this research, investigations were conducted to determine the longitudinal static and dynamic stability effect of Trimaran WIG craft during takeoff and to verify the factors affecting its stability. Two parameters considered are aerodynamic and hydrodynamic characteristics. The investigation resorts to vortex lattice method and examines the effects of flat ground and end plate on the performance of aerodynamic characteristic of the WIG craft. Planing hull has been chosen for the hull shape of the WIG craft due to higher speed takeoff. The hydrodynamics of prismatic planing surfaces, presented by Savitsky, is used to calculate the hydrodynamic characteristic. Numerical result is compared to the experimental results and against published data. The Static Stability Margin (SSM) for longitudinal static stability of Trimaran WIG model has been investigated and using the classical aircraft motion modification and calculating the aerodynamic, hydrostatic and hydrodynamic forces, the complete equation of motion that uses a small perturbation assumption for WIG during takeoff has been derived and solved. Finally, dynamic stability for Trimaran WIG during take-off has been investigated and analyzed using Routh-Hurwitz Stability Criterion and Control Anticipation Parameter (CAP).

A Vortex-Lattice Modeling Approach for Free-Surface Effects on Submerged Bodies and Propellers

Abstract: A vortex-lattice modeling approach is proposed for investigating the free-surface effects on the hydrodynamics of submerged moving bodies and the propeller in the frame of the potential flow theory. The bodies, the propeller, and the free surface waves generated by them are modeled uniformly by vortex lattices. By fulfilling simultaneously the non-penetration boundary condition on the body surface (or on the camber surface for a propeller) and the linearized free-surface boundary condition, a set of linear algebraic equations can be established and solved for the vortex strengths. The vortex lattices for modeling the body- or propeller-generated waves are located slightly above the still water surface, while those for modeling the body are located on the exact body surface. In the case of the propeller, the vortex-lattice lifting-surface model is employed at present and combined with the vortex-lattice free-surface model. A number of test cases are given to investigate the convergence property and accuracy of the proposed approach, in terms of body-surface velocity or pressure distributions, as well as the lift and the wave-making resistance. Then the free-surface effects on quasi-steady propeller hydrodynamics are simulated and investigated at different submerged depths.

Numerical calculation of interaction of propeller slipstream on flowfield over a complete aircraft

Abstract: A lifting surface analysis of vortex lattice method is completed. The coupling between the slipstream and the flow over the aircraft is obtained by using the Von Neumann condition at each control point of the aircraft and propeller panels. The slipstream contraction which definitely exists behind the propeller has been accounted. Practical computations for Y\|7 aircraft with double propellers show that the influences of the slipstream on the lift characteristics with deflected flaps and on the pitching moment coefficient of the complete aircraft are quite obvious. The computation results are in good agreement with experiment data. This method can also be applied to multi and single propeller aircraft.

Nonlinear Filter Formulation for Rapid Estimation of Damaged Aircraft Performance

Abstract: Estimation of aerodynamic models of damaged aircraft using an innovative differential vortex lattice method tightly coupled with extended Kalman filters is discussed. The approach exploits prior knowledge about the undamaged aircraft to reduce the order of the estimation problem. Three different extended Kalman filter formulations are given, together with a comparative analysis. An approach for designing test maneuvers to improve the observability of the system dynamics is also discussed. Algorithms given in this paper can be used as the basis for online derivation of aircraft performance model, which can then form the basis for designing safe landing guidance laws for damaged aircraft. I. Introduction daptive control of damaged aircraft is being investigated at NASA and other aerospace research laboratories in the U.S. 1,2 The focus of these research efforts has been in maintaining control over the attitude dynamics of the damaged aircraft. Assuming that the aircraft remains controllable at its current flight conditions, it is important to be able to predict its performance at other flight conditions in order to derive maneuver constraints that should be enforced to ensure safe transition of the aircraft to landing configuration. The objective of the research discussed in this paper is to develop estimation schemes for rapidly extracting the aerodynamic parameters of damaged aircraft to enable the assessment of aircraft performance. The performance data of interest include flight envelope boundaries and maneuver limits. This data can form the basis for the design of safe landing guidance laws. Several innovative concepts have been advanced in this paper. Firstly, a rapid approach for deriving aerodynamic models of damaged aircraft termed as the Differential Vortex Lattice Method (DVLM) was developed. This approach recasts the well known Vortex Lattice Method (VLM) 3 to reduce the dimension of the aerodynamic problem. The DVLM formulation exploits prior knowledge about the airframe to create a low-order computational methodology for relating the changes in the vehicle geometry due to damage to its aerodynamic parameters. This low-order method can be implemented in real-time onboard for the aircraft to provide estimates of the aerodynamic parameters for use in the computation of flight envelope and maneuver limits, and for adaptive guidance law synthesis. Approaches for estimating the maneuver limits and structural dynamic characteristics are also outlined. Secondly, the Extended Kalman filtering (EKF) approach 4-6 is employed for online estimation of damaged aircraft parameters based on the DVLM. Design of maneuvers for enhancing the observability of the damaged aircraft model parameters is also discussed. The model parameters derived from the estimator can be used for computing the flight envelope and the maneuver limits. These can then be used in the synthesis of safe guidance laws for landing the aircraft. Unlike the airframe stabilization problem, the guidance task is almost entirely based on predictive information about the aircraft dynamics. For instance, landing guidance requires the aircraft to slow down to the approach speeds while descending to the correct altitude at a specified heading. Since damaged aircraft may have a high drag and lower stall angle of attack, the aircraft energy has to be carefully managed to ensure that adequate lift is maintained until flare altitude and touchdown. This will require energy conservative maneuvers and descent strategies. Since damaged aircraft may not be able to employ all its high-lift devices, its speed must be carefully managed to avoid premature loss of lift. These factors make it important to derive a reasonably accurate performance model of the aircraft for the design of a viable guidance system. It may be noted that although most inner-loop flight control systems operate well within the limits of controllability most of the time, the guidance task often involves operating near the edges of the operational envelope.