Quantitative Assessment of Dynamic Stability Characteristics for Jet Transport in Sudden Plunging Motion

The main objective of this article is to present a training program of loss control prevention for the airlines to enhance aviation safety and operational efficiency. The assessments of dynamic stability characteristics based on the approaches of oscillatory motion and eigenvalue motion modes for jet transport aircraft response to sudden plunging motions are demonstrated in this article. A twin-jet transport aircraft encountering severe clear-air turbulence in transonic flight during the descending phase will be examined as the study case. The flight results in sudden plunging motions with abrupt changes in attitude and gravitational acceleration (i.e. the normal load factor). Development of the required thrust and aerodynamic models with the flight data mining and the fuzzy-logic modeling techniques will be presented. The oscillatory derivatives extracted from these aerodynamic models are then used in the study of variations in stability characteristics during the sudden plunging motion. The fuzzy-logic aerodynamic models are utilized to estimate the nonlinear unsteady aerodynamics while performing numerical integration of flight dynamic equations. The eigenvalues of all motion modes are obtained during time integration. The present quantitative assessment method is an innovation to examine possible mitigation concepts of accident prevention and promote the understanding of aerodynamic responses of the jet transport aircraft.

The Development of a Flight Test Platform to Study the Body Freedom Flutter of BWB Flying Wings

A flight test platform is designed to conduct an experimental study on the body freedom flutter of a BWB flying wing, and a flight test is performed by using the proposed platform. A finite element model of structural dynamics is built, and unsteady aerodynamics and aeroelastic characteristics of the flying wing are analyzed by the doublet lattice method and g-method, respectively. Based on the foregoing analyses, a low-cost and low-risk flying-wing test platform is designed and manufactured. Then, the ground vibration test is implemented, and according to its results, the structural dynamics model is updated. The flight test campaign shows that the body freedom flutter occurs at low flight speed, which is consistent with the updated analytical result. Finally, an active flutter suppression controller is designed using a genetic algorithm for the developed flying wing for future tests, considering the gains and sensor location as design parameters. The open- and closed-loop analyses in time- and frequency-domain analyses demonstrate that the designed controller can improve the instability boundary of the closed-loop system effectively.

Static Analysis of Unsteady Aerodynamics Wake of Simplified Helicopter Model Via Simulation Work

Computational tools have led and helped researchers in providing advanced results, notably in rotorcraft research, as flow around the helicopter is dominated by complex aerodynamics and flow interaction phenomena. This research work aimed to evaluate the aerodynamic computational results on a simplified model helicopter when the model was subjected to the angles of attack 0°, -5°, -15°, and -20°, respectively. The study also examined the unsteady flow behaviour on the three-dimensional elliptical shape of a fuselage equipped with a rotor hub of the single rotor blade. The computational domain for the aerodynamic flow field was created within the size of 7 m (length) x 5 m (width) x 5 m (height). Results showed that an increase in the angle of attack in the rotor component caused additional drag of about 34% to 45% whilst the fuselage component contributed about 55% to 65% to drag increment. Also, a significant value of total pressure from -235 Pa to 250 Pa demonstrated along the simplified model helicopter distinctly showed that the complexity of geometry caused adverse pressure. The findings of this research work could potentially improve the understanding of complex flow surrounding the helicopter that has always baffled the aerodynamicists.

Geometric-control formulation and averaging analysis of the unsteady aerodynamics of a wing with oscillatory controls

Differential-geometric-control theory represents a mathematically elegant combination of differential geometry and control theory. Practically, it allows exploitation of nonlinear interactions between various inputs for the generation of forces in non-intuitive directions. Since its early developments in the 1970s, the geometric-control theory has not been duly exploited in the area of fluid mechanics. In this paper, we show the potential of geometric-control theory in the analysis of fluid flows, exemplifying it as a heuristic analysis tool for discovery of symmetry-breaking and unconventional force-generation mechanisms. In particular, we formulate the wing unsteady aerodynamics problem in a geometric-control framework. To achieve this goal, we develop a reduced-order model for the unsteady flow over a pitching–plunging wing that is (i) rich enough to capture the main physical aspects (e.g. nonlinearity of the flow dynamics at large angles of attack and high frequencies) and (ii) efficient and compact enough to be amenable to the analytic tools of geometric nonlinear control theory. We then combine tools from geometric-control theory and averaging to analyse the developed reduced-order dynamical model, which reveals regimes for lift and thrust enhancement mechanisms. The unsteady Reynolds-averaged Navier–Stokes equations are simulated to validate the theoretical findings and scrutinize the underlying physics behind these enhancement mechanisms.

CFD analysis of a Darrieus Vertical-Axis Wind turbine installation on the rooftop of a buildings under turbulent inflow conditions

The behavior of a rooftop mounted generic H-rotor Darrieus vertical axis wind turbine (H-VAWT) is investigated numerically in realistic urban terrain. The interaction of the atmospheric boundary layer with the different buildings, topography, and vegetation present in the urban environment leads to the highly turbulent inflow conditions with continuously changing inclination, and direction. Consequently, all these factors can influence the performance of a VAWT significantly. In order to simulate a small H-VAWT at rooftop locations in the urban terrain under turbulent inflow conditions, a computational approach is developed. First, the flow field in the terrain is initialized and computed with inflow turbulence. Later, the wind turbine grids are superimposed for further computation in the turbulent flow field. The behavior of the H-VAWT is complex due to the 3D unsteady aerodynamics resulting from continuously changing the angle of attack, blade wake interaction, and dynamic stall. To get more insights into the behavior of a rooftop mounted H-VAWT in turbulent flow, high fidelity DDES simulations are performed at different rooftop positions and compared the results against the behavior at uniform inflow conditions in the absence of inflow turbulence, built environment. It is found that the performance of wind turbine is significantly increased near the rooftop positions. The skewed flow at the rooftop location increases the complexity. However, this effect contributes positively to increasing the performance of wind turbines.

Parametric whirl flutter study using different modelling approaches

This paper demonstrates the importance of assessing the whirl flutter stability of propeller configurations with a detailed aeroelastic model instead of local pylon models. Especially with the growing use of electric motors for propulsion in air taxis and commuter aircraft whirl flutter becomes an important mode of instability. These configurations often include propeller which are powered by lightweight electric motors and located at remote locations, e.g. the wing tip. This gives rise to an aeroelastic instability called whirl flutter, involving the gyroscopic whirl modes of the engine. The driving parameters for this instability are the dynamics of the mounting structure. Using a generic whirl flutter model of a propeller at the tip of a lifting surface, parameter studies on the flutter stability are carried out. The aeroelastic model consists of a dynamic MSC.Nastran beam model coupled with the unsteady ZAERO ZONA6 aerodynamic model and strip theory for the propeller aerodynamics. The parameter studies focus on the influence of different substructures (ranging from local engine mount stiffness to global aircraft dynamics) on the aeroelastic stability of the propeller. The results show a strong influence of the level of detail of the aeroelastic model on the flutter behaviour. The coupling with the lifting surface is of major importance, as it can stabilise the whirl flutter mode. Including wing unsteady aerodynamics into the analysis can also change the whirl flutter behaviour. This stresses the importance of including whirl flutter in the aeroelastic stability analysis on aircraft level.