This article proposes a safety control scheme for quadrotor unmanned aerial vehicle (UAV) to counteract ground effect and blade damage. The impacts of ground effect and blade damage are ...quantitatively analyzed in the established model. The proposed safety control scheme consists of position and attitude loops. Specifically, a proportional and derivative controller is designed as a baseline control with acceleration feedforward in the position loop. A disturbance observer (DO) using the measured Euler angles is exploited to estimate the lumped disturbance forces. The developed DO can effectively mitigate the estimation deviation caused by the angle tracking error. Subsequently, differential flatness theory is used to obtain the Euler angle references and the derivatives. In the attitude loop, sliding mode control and fixed-time sliding mode observer (SMO) are integrated to deal with ground effect and blade damage promptly. To demonstrate the effectiveness of the proposed safety control scheme, flight experiments are carried out, where the quadrotor UAV flies close to the rugged ground in the presence of blade damage.
In the present work, the aerodynamic performance of the Caradonna and Tung and S-76 in hover were investigated using a simplified concept of multiple reference frame (MRF) technique in the context of ...high-order Monotone Upstream Centred Scheme for Conservation Laws (MUSCL) cell-centred finite volume method. In the present methodology, the frame of reference is defined at the solver level by a simple user input avoiding the use of mesh interface to handle the intersections between frames of reference. The calculations were made for both out-of-ground-effect (OGE) and in-ground-effect (IGE) cases and compared with experimental data in terms of pressure distribution, tip-vortex trajectory, vorticity contours and integrated thrust and torque. The predictions were obtained for several ground distances and collective pitch angle at tip Mach number of 0.6 and 0.892.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Dynamics and Instabilities of Vortex Pairs Leweke, Thomas; Le Dizès, Stéphane; Williamson, Charles H.K
Annual review of fluid mechanics,
01/2016, Volume:
48, Issue:
1
Journal Article
Peer reviewed
Open access
This article reviews the characteristics and behavior of counter-rotating and corotating vortex pairs, which are seemingly simple flow configurations yet immensely rich in phenomena. Since the ...reviews in this journal by
Widnall (1975)
and
Spalart (1998)
, who studied the fundamental structure and dynamics of vortices and airplane trailing vortices, respectively, there have been many analytical, computational, and experimental studies of vortex pair flows. We discuss two-dimensional dynamics, including the merging of same-sign vortices and the interaction with the mutually induced strain, as well as three-dimensional displacement and core instabilities resulting from this interaction. Flows subject to combined instabilities are also considered, in particular the impingement of opposite-sign vortices on a ground plane. We emphasize the physical mechanisms responsible for the flow phenomena and clearly present the key results that are useful to the reader for predicting the dynamics and instabilities of parallel vortices.
This paper focuses on the development of Ground Effect Craft (GEC). The ultimate objective of this paper is to comprehensively outline all publicly disclosed and well-known GECs. The scope of this ...paper encompasses a review of the design challenges and architectures associated with GECs that have been prevalent for more than 60 years. It delves into research, development, and enhancements of existing GECs throughout their history. In conclusion, considering current technological advances, GECs present substantial opportunities and potential to evolve into a viable mode of transportation, effectively bridging the gap between aircraft and ships. The incentive to overcome the economic challenges associated with fabricating and operating GECs is worthwhile, encouraging exploration and development toward a commercially viable GEC.
This paper presents an experimental and numerical study of the aerodynamics of a moderate-scale rotor hovering in the Extreme Ground Effect (EGE) where rotor height-off-ground is below half the rotor ...radius. The tip vortex field was visualized by using the PIV technique. The aerodynamic performance, tip vortex trajectory, wall jet characteristics, surface pressure and velocity fields were measured and analyzed. To explore more deeply the flow mechanisms of the extreme ground effect, Detached Eddy Simulation (DES) was conducted on completely structured meshes. The results showed significant deviations of the rotor performance in EGE from that in Regular Ground Effect (RGE) with the rotor heights of more than half the rotor radius. Moreover, the flow structures of the rotor in EGE are considerably complex, such as the wall jet and groundwash flow separation. The rotor wake flow and tip vortices impact the ground more frequently, resulting in distinctive characteristics of the surface pressure and velocity fields in EGE.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The vertical drag or download on the structure under the rotor of a helicopter caused by the downwash deteriorates hovering performance. On the other hand, the partial ground effect provided by the ...structure under the rotor improves hovering performance. The design of the fuselage planform should simultaneously consider these aerodynamic interactions, namely the effect of download and the ground effect. This is more important for winged helicopters, which have a large planform area. In this research, as a first step, the download and the partial ground effect of a disk-like structure are investigated to obtain general knowledge of aerodynamic interaction. Experimental parameters are the disk radius, the distance between the rotor and the disk, and the root cutout of the rotor. It is revealed that when the root cutout is relatively small, if the disk radius is up to about half the size of the rotor radius, hovering performance does not deteriorate. Then, as a second step, it is shown that this general knowledge of the disk can be successfully applied to the problem of determining the flap width of winged helicopters.
A practical mathematical model with low computational time and good accuracy is applied to investigate the aerodynamic characteristics and static height stability of the compound wing-in-ground ...effect (WIG). The compound WIG consists of a main wing with low aspect ratio and an endplate, and an outer wing with high aspect ratio. To validate the present mathematical model, a numerical simulation is performed so that numerical results had a good agreement with the experimental data. The analysis shows that the main wing is useful in the extreme ground effect zone and the outer wing enhances performance of the compound WIG in the weak ground effect zone. In order to satisfy the static height stability of the compound WIG it is evaluated by Irodov's criterion. Influence of junction position of outer wing on the main wing is investigated on the static height stability of compound WIG. A comparison of Irodov's criterion shows that static height stability improves with moving the outer wing position backward into the trailing edge of the main wing and this led to a decrease in the tail area. The proposed mathematical model could be appropriate for aerodynamic optimization of WIG crafts with the compound wing.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Autonomous vehicles are nowadays one of the most important technologies that will be incorporated to every day life in the next few years. One of the most promising kind of vehicles in terms of ...efficiency and sustainability are those known as Wing-in-Ground crafts, or WIG crafts, a family of vehicles that seize the proximity of ground to achieve a flight with low drag and high lift. However, this kind of crafts lacks of a sound theory of flight that can lead to robust control solutions that guarantees safe autonomous operation in all the cruising phases.In this paper we address the problem of controlling a WIG craft in different scenarios and using different control strategies in order to compare their performance. The tested scenarios include obstacle avoidance by fly over and recovering from a random disturbance in vehicle attitude. MPC (Model Predictive Control) is tested on the complete nonlinear model, while PID, used as baseline controller, LQR (Linear Quadratic Regulator) and adaptive LQR are tested on top of a partial feedback linearization. Results show that LQR has got the best overall performance, although it is seen that different design specifications could lead to the selection of one controller or another.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A water borne WIGcraft in principle, generates much higher lift than that of an equivalent free-flight airplane, air-borne WIGcraft and planing boats due to the complementary ground effect ...aerodynamic, hydrodynamic and hydrostatic lift generated by the wings and submerged portion of the hull surfaces. However, the coupling of the ground effect aerodynamics and hydrodynamics of the vehicle, compounded by hull-generated water-spray impinging on its wings presents challenges when predicting dynamic forces on the vehicle. Capturing the complex air-water flow about the wings, and its effects on the dynamic lift on the vehicle require advanced and computationally expensive high fidelity nonlinear numerical solution. This paper proposes a semi-empirical model as a simplified alternative to estimate the dynamic lift on the vehicle. The model was developed based on the theories of ground effect aerodynamics and planing watercraft hydrodynamics, as well as physical observations from fully constrained experiments of a multihull watercraft model with and without wings. The various elemental components of the water-borne WIGcraft dynamic lift including ground-effect and hull-generated water-spray induced lift on the wings were estimated. To ensure simplicity and consistency in coupling the aerodynamic and hydrodynamic lift coefficients, an equivalent hydrodynamic lift coefficient was proposed for the aerodynamic lift coefficient of the wings of the vehicle. The results of the proposed semi-empirical model and that of the fully constrained model experiments are in satisfactory agreement. The results of the total dynamic lift of the water-borne WIGcraft suggest that for a water-borne WIGcraft operating at large draughts with water-spray impinging on its wings, the effect of the wings’ proximity to the free surface water is secondary. The contribution of the hull generated water spray to the total dynamic lift force is significant.
•The novel contributions made by this paper to existing body of literature on high performance marine vehicle are highlighted below.•An equivalent hydrodynamic coefficient was introduced for aerodynamic coefficient.•New relation for hull-generated water spray lift on waterborne WIGcraft was developed.•New relation for ground effect on the wings of a waterborne WIGcraft was developed.•New semi-empirical model for dynamic lift on a water borne WIGcraft was developed.•Ground effect is secondary for waterborne WIGcraft when spray impinges on its wings.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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