Large Camber Angles Research Articles

Design Requirements for Personal Mobility Vehicle (PMV) with Inward Tilt Mechanism to Minimize Steering Disturbances Caused by Uneven Road Surface

The Personal Mobility Vehicle (PMV), which has an inward-tilting angle, turns with lateral force due to a large camber angle, so it is necessary to consider the lateral movement of the tire vertical load axis during turning. Although the steering torque mechanisms are very different from those of automobiles, there are not many studies of the steering torque mechanisms of PMVs. In this paper, based on the effects of the force of six components acting on the tires, a method for setting the steering axis specifications is derived, including the geometrical minimization of steering moment disturbance due to the vertical load reaction force during turning. Automobile tires have a significant ground camber angle when traveling on rutted roads, but they do not have it on slanted roads because the vehicle body tilts along the road surface. On the other hand, in PMVs, the vehicle body always keeps upright when traveling both on slanted roads and on rutted roads. Therefore, the tires have ground camber angles on both types of road surface. We study the straight running ability under such road surface disturbances based on the geometrical minimization of steering moment disturbance due to the vertical load reaction force during turning. This straight running ability can be a remarkable strong point of PMVs with an inward tilt mechanism. In this study, it was proved that the steering axis parameters can be derived uniquely by taking into consideration the requirement to zero the moment (disturbance) around the steering axis due to the reaction force against the vertical load at all internal tilt angles.

An extended LuGre-brush tyre model for large camber angles and turning speeds

ABSTRACT This paper presents a novel tyre model which combines the LuGre formulation with the exact brush theory recently developed by the authors, and which accounts for large camber angles and turning speeds. Closed-form solutions for the frictional state at the tyre-road interface are provided for the case of constant slip inputs, considering rectangular and elliptical contact patches. The steady-state tyre characteristics resulting from the proposed approach are compared to those obtained by employing the standard formulation of the LuGre-brush tyre models and the exact brush theory for large camber angles. Then, to cope with the general situation of time-varying slips and spins, two approximated lumped models are developed that describe the aggregate dynamics of the tyre forces and moment. In particular, it is found that the transient evolution of the tangential forces may be approximated by a system of two coupled ordinary differential equations (ODEs), whilst the dynamics of the self-aligning moment may be described by combining two systems of two coupled ODEs. Given its stability properties and ease of implementation, the lumped one may be effectively employed for vehicle state estimation and control purposes.

Analytical results in transient brush tyre models: theory for large camber angles and classic solutions with limited friction

This paper establishes new analytical results in the mathematical theory of brush tyre models. In the first part, the exact problem which considers large camber angles is analysed from the perspective of linear dynamical systems. Under the assumption of vanishing sliding, the most salient properties of the model are discussed with some insights on concepts as existence and uniqueness of the solution. A comparison against the classic steady-state theory suggests that the latter represents a very good approximation even in case of large camber angles. Furthermore, in respect to the classic theory, the more general situation of limited friction is explored. It is demonstrated that, in transient conditions, exact sliding solutions can be determined for all the one-dimensional problems. For the case of pure lateral slip, the investigation is conducted under the assumption of a strictly concave pressure distribution in the rolling direction.

Impact Evaluation of Full-Span Slot and Blade-End Slot on Performance of a Large Camber Compressor Cascade

It has been proved that suitable slot structure of compressor slotted blade can generate high-momentum jet flow through pressure difference between the pressure and suction surface, the slot jet flow can reenergize the local low-momentum fluid to effectively eliminate the flow separation. In order to investigate and evaluate the impact of full-span slot and blade-end slot on the performance of the post-loaded blade, which has serious flow separation on the suction surface both near blade midspan and endwall, a diffusion stator cascade with large camber angle is selected as the research object. Firstly, the blade-end slotted scheme and the full-span slotted scheme are set up. Then the performance of datum cascade and two slotted cascades is computed in the wide incidence angle range of -8º to 6º at the Mach number of 0.7, the corresponding blade-chord-based Reynolds number 〖Re〗_C is 7.7×10^5. Finally, the performance of the three cascades is analyzed and compared. The results show that, in the computational incidence angle range, both of the two slotted schemes can reduce the total pressure loss for datum cascade and enhance its pressure diffusing capability. However, compared with the blade-end slot, the full-span slot has a better comprehensive control effect on the corner separation and the boundary layer separation near blade midspan, hence, compared with those of blade-end slotted cascade, the total pressure loss coefficients and the static pressure coefficients of full-span slotted cascade are respectively further decreased and increased. Under the blowing effect of full-span slot jet, the total pressure loss coefficients of datum cascade are significantly decreased, ranging as high as 21.2%, 23.1%, 24.5% and 23.4% under the incidence angles of 0°, 2°, 4° and 6°, respectively. The full-span slotted scheme has a better adaptability to wide incidence angle range, it can effectively broaden the available incidence angle range for datum cascade.

Passive Control with Blade-End Slots and Whole-Span Slot in a Large Camber Compressor Cascade

Suitable slot structure of the compressor blade can generate high-momentum jet flow through pressure difference between the pressure and suction surface, it has been proved that the slot jet flow can reenergize the local low-momentum fluid to effectively suppress the flow separation on the suction surface. In order to explore a slotted method for better comprehensive suppressing effects on the boundary layer separation near blade midspan and the three-dimensional corner separation, a diffusion stator cascade with large camber angle is selected as the research object. Firstly, the Slotted_1 and Slotted_2 whole-span slotted schemes are set up, then the Slotted_3 scheme with whole-span slot and blade-end slots is proposed, finally the performance of original cascade and slotted cascades is computed under a wide range of incidence angles at the Mach number of 0.7. The results show that: in the full range of incidence angles, compared with the whole-span slotted cascades, the development of the endwall secondary flow on the suction surface of Slotted_3 cascade is effectively suppressed, the degree of the mutual interference between the secondary flow and the main flow is reduced. Besides, on the suction surface of Slotted_3 cascade, the boundary layer separation near blade midspan and the corner separation are basically eliminated. As a result, compared with those of original cascade, the total pressure losses of Slotted_3 cascade are reduced in the full range of incidence angles, and its operating range of incidence angles is broadened. Moreover, compared with the whole-span slotted schemes, Slotted_3 scheme has a better adaptability to wide range of incidence angles.

Brush tyre models for large camber angles and steering speeds

In this paper, we discuss three improved brush models. The first one deals with the coupling between the slip and spin parameters and is valid for relatively high steering speed and small camber angles; the second one is more complex and considers the presence of a two-dimensional velocity field inside the contact patch due to large camber angles; the third one is more general and combines both the previous formulations. For the last two models, the investigation is conducted with respect to a rectangular contact patch, for which we show that three different regions can be identified, each of them corresponding to a different steady-state solution for the deflection of the bristle. Furthermore, from the transient analysis it emerges that each region can be in turn separated into an area in which steady-state conditions reign and another one in which the transient solution takes place. An asymptotic analysis is carried out for the three models and it is shown that the solutions are equivalent to the ones predicted by the standard brush theory for small values of the spin ratio and camber angle. Finally, a comparison is performed amongst the models to highlight the differences in the predicted tyre characteristics.

Omnidirectional Mobility Following Through Trochoidal Trajectory

The trochoid is a geometrically complete solution for realizing omnidirectional mobility with a rotating mechanism. The proposed mechanism is implemented as a novel omnidirectional vehicle with following a geometrically complete trochoidal trajectory. Because the mechanism has a large camber angle, it has an improved ability to travel past rough terrain as compared to a regular vehicle with regular wheels. In this paper, a complete mechanical control using link mechanism to generate not only the steering angle and camber angle for an ideal trochoidal wave but also the angular velocity of the wheel axis is proposed.

Research on Dynamics of Two Wheel Vehicle with Large Camber Angle

Research on Dynamics of Two Wheel Vehicle with Large Camber Angle

A Study of the Ditch Fall-over Test Method Using Numerical Simulation

Rollover tests are performed to design the algorithms for deployment of countermeasures to mitigate occupant ejection in rollover situations. The ditch fall-over test is one of the rollover test methods in which a vehicle on a steep slope, representing a ditch embankment, is subjected to a forced steering operation that results in a turnover. An accurate prediction method is needed to determine the specifications of the ditch fall-over test equipment and test conditions because a test-based trial-and-error process involves high cost of performing repeated experiments and preperation for various types of related test equipment. This paper presents a newly developed numerical simulation method for simulating vehicle behavior in ditch fall-over tests. The vehicle model used in the simulation incorporates a finite element tire model for calculating the contact forces to a steep slope in a rollover situation characterized by large contact patch deformation with very large camber angles relative to the slope, an operating condition that ordinary vehicles cannot handle. The vehicle model also includes the suspension systems, steering system and inertial properties of the vehicle. Under various test conditions, the simulation results agreed well with those of actual ditch fall-over test data to judge whether turnover occurred or not and also the dynamic response such as vehicle roll rate. Simulations were conducted to investigate the test equipment specifications and test conditions for a vehicle. It was found that the slope angle, the friction coefficient of the slope, initial vehicle velocity and the sectional shape of the slope at the top influence vehicle turnover behavior. Language: en

An improved Magic Formula/Swift tyre model that can handle inflation pressure changes

This paper describes extensions to the widely used TNO MF-Tyre 5.2 Magic Formula tyre model. The Magic Formula itself has been adapted to cope with large camber angles and inflation pressure changes. In addition, the description of the rolling resistance has been improved. Modelling of the tyre dynamics has been changed to allow a seamless and consistent switch from simple first-order relaxation behaviour to rigid ring dynamics. Finally, the effect of inflation pressure on the loaded radius and the tyre enveloping properties is discussed and some results are given to illustrate the capabilities of the model.

Enhancing aerodynamic performances of a high-turning compressor cascade via boundary layer suction

Experimental investigation was carried out to study the effect of suction positions and suction flow rates on the aerodynamic performance of a compressor cascade with a large camber angle. The ink-trace flow visualization was conducted and the flow fields of the cascade were also measured. Three types of boundary layer suction configurations are compared, i.e. the suction surface suction, the endwall suction and the compound suction. Experimental results show that the large amount of suction flow rate gains more losses reduction than the small amount for a certain proper suction configuration, but the speed of loss decline slows down as the suction flow rate goes on increasing. Boundary layer suction on the suction surface obviously enhances the ability of the boundary layer around the midspan to withstand the negative pressure gradient of the flow passage. The range of the suction surface corner is also decreased. If the suction slot locates in the corner separation region where severe separation has happened, the flow separation will be terminated at the slot and redevelop downstream. And boundary layer suction on the endwall mainly influences the endwall corner region in remarkably delaying, lessening and reorganizing the corner separation. While the whole flow field is remarkably improved at both midspan and the corner region in the compound suction schemes. At higher suction flow rates, the aerodynamic performance of the compressor cascade is better than that with boundary layer suction simply on the suction surface or on the endwall. When the suction flow rate is 1.5% of the inlet mass flow, the compound suction scheme achieves a maximum loss reduction of 17% compared with the cascade without boundary layer suction.

Effects of Boundary Layer Suction on Aerodynamic Performance in a High-load Compressor Cascade

This article is aimed to experimentally validate the beneficial effects of boundary layer suction on improving the aerodynamic performance of a compressor cascade with a large camber angle. The flow field of the cascade is measured and the ink-trace flow visualization is also presented. The experimental results show that the boundary layer suction reduces losses near the area of midspan in the cascade most effectively for all suction cases under test. Losses of the endwall could remarkably decrease only when the suction is at the position where the boundary layer has separated but still not departed far away from the blade surface. It is evidenced that the higher suction flow rate and the suction position closer to the trailing edge result in greater reduction in losses and the maximum reduction in the total pressure loss accounts to 16.5% for all cases. The suction position plays a greater role in affecting the total pressure loss than the suction flow rate does.

Experimental Study of Bowed-twisted Stators in an Axial Transonic Fan Stage

Bowed-twisted stators with large camber angles have been developed to replace the conventional tandem stators in an axial transonic fan stage working at high subsonic speeds. Experimental study is carried out on both stages with tandem stators and with bowed-twisted stators. Compared to the tandem stators, the bowed-twisted stators change the distribution of the low-energy fluid and the potential high-energy fluid at the compressor outlets, reduce the endwall loss significantly, improve the aerodynamic matching of rotors and stators, and eventually increase the fan stage performances. The aerodynamic performances of the fan stage at different operating points are compared and contrasted. The results show that the transonic fan stage with bowed-twisted stators has better aerodynamic performances. It is thus suggested that the bowed-twisted stators with large camber angles be popularized into the high-loaded transonic fan designs.

Pressure Measurement on Suction Surface of a Single Vane Using Pressure-sensitive Paint

Global pressure distribution on the suction surface of a single vane in a transonic cascade wind tunnel is measured with the help of intensity-based pressure-sensitive paint (PSP) technique using a type of temperature-insensitive fluorescent paint and a self-made measurement system. This measurement is conducted at the outlet of the cascade wind tunnel at the Mach numbers 0.3 and 0.4, attack angle about −20°, ambient pressure 95.4 kPa and temperature 15 °C. The vane under study owns a large camber angle of about 40° and 4×10 pressure ports on its suction surface with a steel cubic stand attached. It is fixed vertically on the lower guide steel plate at the outlet through the stand for convenient acquisition of images. Conventional electronic static pressure (ESP) measurement is also fulfilled simultaneously with an ESP scanner for comparison. The method of intensity-based PSP technique is introduced, especially, with the self-made PSP system. The operating sequence of PSP measurement for improved accuracy is also proposed. The practical steps of image processing are described. As an image registration, target alignment is introduced after the 4×10 pressure ports have been selected as targets. The comparison of PSP results with ESP data shows that the maximum error remains within 6.5%.

Analysis of Aerodynamic Performance in an Annular Compressor Bowed Cascade with Large Camber Angles

The effects of positively bowed blade on the aerodynamic performance of annular compressor cascades with large camber angle were experimentally investigated under different incidences. The distributions of the exit total pressure loss and secondary flow vectors of compressor cascades were analyzed. The static pressure was measured by tapping on the cascade surfaces, and the ink-trace flow visualizations were conducted. The results show that the value of the optimum bowed angle and optimum bowed height decrease because of the increased losses at the mid-span with the increase of the caber angle. The C-shape static pressure distribution along the radial direction exists on the suction surface of the straight cascade with large r camber angles. When bowed blade is applied, the larger bowed angle and larger bowed height will further enhance the accumulation of the low-energy fluid at the mid-span, thus deteriorate the flow behavior. Under <TEX>$60^{\circ}$</TEX> camber angle, flow behavior near the end-wall region of some bowed cascades even deteriorates instead of improving because the blockage of the separated flow near the mid-span keeps the low-energy fluid near the end-walls from moving towards the mid-span region, and as a result, a rapid augmentation of the total loss is easy to take place under large bowed angle. With the increase of camber angle, the choice range of bowed angle corresponding to the best performance in different incidences become narrower.

Multi-body modelling and analysis into the non-linear behaviour of modern motorcycles

The stationary and periodic motion of a motorcycle under typical and extreme running conditions on a straight road and during cornering is investigated. The motorcycle model consists of six rigid bodies: a rear frame, a steering head with handlebar and the suspended part of the front fork, the unsuspended part of the front fork, a rear swing arm, and two wheels. The tyre force model deals effectively with large camber angles and combined longitudinal and lateral slips plus normal spin rate. The equations of motion are generated in a symbolic form by the multi-body dynamics program AutoSim. For analysing solutions of the equations of motion, the numerical continuation program AUTO 97 is employed. Bifurcation diagrams for a motorcycle running straight ahead or in a circle are presented and discussed. The motorcycle can have three basic modes of instability: capsize, wobble, and weave mode. The results indicate that aerodynamic drag has a tendency to make the wobble mode more damped and the weave mode less damped. The emerging bifurcating periodic solutions are mostly of the subcritical kind for the weave and of the supercritical kind for the wobble.

Modelling of tire overturning moment and loaded radius

For evaluation of vehicle handling, subjective assessment is currently almost the only criterion. For the purpose of reducing cycle time and avoiding error of subjective assessment, the close-loop objective evaluation system through computer simulations has become an inevitable choice [Gwanghun, G.I.M. and Yongchul, C.H.O.I., 2001, Role of tire modeling on the design process of a tire and vehicle system. ITEC ASIA 2001, Busan, Korea, September 18–20; Guo, K., Ding, H., Zhang, J., Lu, J. and Wang, R., 2003, Development of longitudinal and lateral driver model for autonomous vehicle control. International Journal of Vehicle Design, 36(1), 50–65]. For this reason, the more accurate models of vehicle, tire and driver are necessary. Since structure and operating conditions of tires are very complicated, many researchers have paid more attention to the modeling of tire properties and varieties of tire model have been done to describe the tire behaviour of longitudinal, lateral forces and aligning moment [Pacejka, H.B., 2002, Tyre and Vehicle Dynamics. Butterworth-Heinemann, an imprint of Elsevier Science, ISBN 0-7506-5141-5]. However, there are few studies for the tire overturning moment (TOM), especially under large slip angle and camber angle. For the simulation of vehicle rollover, the expression accuracy of TOM is rather important. In addition, the difference of the loaded radius of left and right tires yields tire roll angle and that also affects vehicle roll behavior. In this paper, the modeling of TOM and loaded radius are presented first, and then the modeling results are compared with tire test data.

A Numerical Investigation of Boundary Layer Suction in Compound Lean Compressor Cascades

This paper is focused on the numerical investigation of boundary layer suction (BLS) via a slot on the suction surfaces of two compound lean compressor cascades with large camber angles as well as a conventional straight compressor cascade for comparison. The objective of the investigation is to study the influence of boundary layer suction on the performance of compound lean compressor cascades, thus to discuss the possibility of the application of boundary layer suction to improve their performance. An extensive numerical study has been carried out under different spanwise lengths, different axial positions of the slots, and different suction flow rates. The results show that the total loss of all three cascades is reduced significantly by boundary layer suction, and the largest reduction occurs at the highest suction flow rate. The axial locations of the slot have little effect on the total loss of the three cascades, which means the slots are opened within the optimal axial range in this case. The slot opened along the full span is the best one to obtain the largest reduction in total loss for all three cascades due to the alleviation of flow separation in the corner between the endwall and the suction surface. Moreover, the flow turning is increased, and pressure rise at the rear of the passage is recovered along the whole blade height via boundary layer suction along the full span, enhancing the working range of the highly loaded compressor cascades.

The relation between contact patch geometry and the mechanical properties of motorcycle tyres

The mechanical properties of motorcycle and scooter tyres have a large influence on the handling and stability of these vehicles. When a two-wheeled vehicle moves along a curvilinear path, there are large camber angles (up to 50°); hence, tyres have a curved cross-section and the contact patch moves and changes its shape when the roll and steer angles are modified by the rider. This paper describes experimental research aimed at studying the influence of the camber angle, vertical load and inflation pressure on the shape of the contact patch and the forces and moments of the tyres. The experimental tests were carried out by means of a rotating-disc machine. The contact patches were measured by making use of a pressure-indicating film. The camber force and twisting torque were related to the vertical load and inflation pressure through the dimensions of the contact patch. New best-fitting equations were developed starting from the brush model. Many experimental results dealing with front and rear tyres are presented and the merits and limitations of the best-fitting equations are discussed.

Dynamic Properties of Motorcycle and Scooter Tires: Measurement and Comparison

Summary Results of an experimental research program dealing with motorcycle and scooter tires are presented. Experimental tests were carried out by means of a rotating disk test machine, which is particularly suited to test tires in the presence of large camber angles. First, the capabilities of the rotating disk machine are discussed and results are compared with the ones obtained by means of other test machines. Then the properties of several motorcycle and scooter tires are presented and compared. The advantage of presenting results in terms of camber and sideslip stiffness is highlighted. The effect of tire working conditions (inflation pressure, load and temperature) is analyzed. Finally the measurement of tire torques is discussed and some results dealing with self-aligning, twisting and rolling resistance torques are presented.