Abstract:The main goal of this study was the experimental investigation of the fluid pressure in the boundary region between wet grip and hydroplaning. In order to gain an insight into the processes in the tire contact area, a test setup was developed to directly measure the fluid pressure in the water film between tire and road. The fluid pressure was measured on an asphalt track for different speeds, water heights and tire patterns on an inner drum test bench. The influence of the examined parameters on the fluid pre… Show more
“…Thus, in these situations, metal-to-metal contact likely occurs between the wheel and track and lubrication pressures are evidently insufficient to counter the applied load and lift the wheel. A similar situation arises for hydro-planing, although the Reynolds numbers reached there are much higher, and the surface topography of the wheel plays an important role (Kulakowski & Harwood 1990;Seta et al 2000;Löwer et al 2020). Somewhat surprisingly, the criterion in (3.1) is clearly violated for many of the higher interactions of the cases with lift-off in figure 12.…”
Section: Wheel Lift-offmentioning
confidence: 65%
“…2000; Löwer et al. 2020). Figure 13.Lift-off threshold during Interaction One as a function of speed, load and surface roughness.…”
Experiments are conducted to explore the rolling of a cylinder over a pool of viscous fluid. The speed, width and loading of the cylinder are varied along with the initial depth and length of the viscous pool. Depending on the conditions, the cylinder will either ride on a lubrication film or remain in solid contact with the underlying substrate. For the former situation, a lubrication theory is presented that describes the pressure underneath the cylinder and the thickness of the film. The theory approximates the flow by the one-dimensional Reynolds equation with the addition of one term, with an adjustable parameter, to account for the flux of fluid to the cylinder sides. Once this parameter is calibrated against experiment, the theory predicts peak lubrication pressures, gap sizes and film thicknesses to within approximately ten per cent. For lubricated rolling, the film splits evenly between the cylinder and substrate downstream of the nip. The printer's instability arises during the splitting process, patterning the residual fluid films on the substrate and cylinder. If the pool length is less than the cylinder circumference, the fluid adhering to the cylinder is rotated back into contact with the substrate, and when there is sufficient adhered fluid a lubrication film forms that can again be modelled by the theory. Conversely, if there is insufficient adhered fluid, no contiguous lubrication film is formed; instead, the pattern from the printer's instability ‘prints’ from the cylinder to the substrate.
“…Thus, in these situations, metal-to-metal contact likely occurs between the wheel and track and lubrication pressures are evidently insufficient to counter the applied load and lift the wheel. A similar situation arises for hydro-planing, although the Reynolds numbers reached there are much higher, and the surface topography of the wheel plays an important role (Kulakowski & Harwood 1990;Seta et al 2000;Löwer et al 2020). Somewhat surprisingly, the criterion in (3.1) is clearly violated for many of the higher interactions of the cases with lift-off in figure 12.…”
Section: Wheel Lift-offmentioning
confidence: 65%
“…2000; Löwer et al. 2020). Figure 13.Lift-off threshold during Interaction One as a function of speed, load and surface roughness.…”
Experiments are conducted to explore the rolling of a cylinder over a pool of viscous fluid. The speed, width and loading of the cylinder are varied along with the initial depth and length of the viscous pool. Depending on the conditions, the cylinder will either ride on a lubrication film or remain in solid contact with the underlying substrate. For the former situation, a lubrication theory is presented that describes the pressure underneath the cylinder and the thickness of the film. The theory approximates the flow by the one-dimensional Reynolds equation with the addition of one term, with an adjustable parameter, to account for the flux of fluid to the cylinder sides. Once this parameter is calibrated against experiment, the theory predicts peak lubrication pressures, gap sizes and film thicknesses to within approximately ten per cent. For lubricated rolling, the film splits evenly between the cylinder and substrate downstream of the nip. The printer's instability arises during the splitting process, patterning the residual fluid films on the substrate and cylinder. If the pool length is less than the cylinder circumference, the fluid adhering to the cylinder is rotated back into contact with the substrate, and when there is sufficient adhered fluid a lubrication film forms that can again be modelled by the theory. Conversely, if there is insufficient adhered fluid, no contiguous lubrication film is formed; instead, the pattern from the printer's instability ‘prints’ from the cylinder to the substrate.
“…More recently, Lower et al 2020 [18] compared the fluid pressure in the contact patch for different tires with various tread patterns on a wet drum test bench. The fluid pressure is shown to be strongly dependent on tread pattern.…”
Section: Impact Of Tread Design On Wet Brakingmentioning
In order to better understand the hydroplaning phenomenon, local velocity measurements of water flow are performed inside the tire grooves of a real car rolling through a water puddle. Velocity fields are obtained by combining refraction Particle Image Velocimetry (r-PIV) illumination, seeding fluorescent particles and either the classical 2D2C or a 2D3C stereoscopic recording arrangements. The presence of some bubble columns inside the grooves is highlighted by separate visualisation using fluorescent contrast technique evidencing two phase flow characteristics. A simple predictive model is proposed supporting the r-PIV analysis. It provides useful information to adjust the focusing distance and to understand the effect of the bubble column presence on the recorded r-PIV images, especially for the seeding particles located in the upper part of the grooves, as fluorescent light is attenuated by the bubbles. Also, the predictions provided by the model are compatible with the measurements. The velocity fields inside the grooves are analysed using ensemble averaging performed over a set of independent snapshots, recorded with the same operating parameters. The variability of the longitudinal velocity distribution measured in a groove for several independent runs is explained by different mechanisms, like the random position of fluorescent seeding particles at various height of the groove, the hydrodynamic interactions between longitudinal and transverse grooves, and the random location of the transverse grooves from one run to an other. Three velocity components in cross-sections of the longitudinal grooves are obtained using the stereoscopic arrangement. They are compatible with the presence of some longitudinal vortices also assumed in the litterature. The number of vortices is shown to be dependent on the aspect ratio characterising a groove's rectangular cross-section. We demonstrate, from measurements performed for several car velocities, that the velocity distribution inside longitudinal grooves shows self-similarity when using specific dimensionless length scale and velocity. Hydrodynamic interactions between longitudinal and transverse grooves are discussed on the basis of a mass budget; a fluid/structure interaction mechanism is proposed in order to correlate the overall direction of the flow in a transverse groove with its location inside the contact zone. Finally some physical mechanisms are suggested for the birth of longitudinal vortices.
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