Vladimir Viktorov

Identification of Discharge Coefficients of Orifice-Type Restrictors for Aerostatic Bearings and Application Examples

In this chapter is described an experimental study conducted in order to identify the supply hole discharge coefficients of externally pressurized gas bearings. Tests were carried out over specific hole, feed pocket and air gap size ranges on pneumatic pads with two types of air feeding systems: annular orifices (inherent orifices) and simple orifices with feed pocket. Air consumption and pressure distributions were measured as a function of supply pressure and air gap height. Discharge coefficients were approximated by an experimental formula based on the Reynolds number and the feeding system geometry. The validity of the formulation found in the study was verified by comparing the numerically calculated pressure distribution with the experimental distribution measured on different pad types. The numerical pressure distribution was calculated using equations for air flow through the supply holes and the Reynolds equations for the air gap.

Numerical and Experimental Development of a Hub+Bearing System for Tire Pressure Control

The paper presents the study of a hub+bearing system for tire pressure monitoring and control. The tire pressure control is of importance to improve vehicle safety and dynamic behavior, and to reduce fuel consumption and emissions. This feature becomes fundamental in the development of fully automated self-driving cars, which recently some important Companies started to study and test. Firstly, a commercial version of such a system was studied experimentally to evaluate the air-flow vs. pressure curves. Then, a 2D numerical model of the system, by using the commercial CFD software Fluent, was developed and a good match was found between the numerical and the experimental results. Subsequently, taking into account the most important geometric parameters that could influence the conductance and also considering the constraints connected to the bearing dimensions, different configurations of the hub+bearing system were studied numerically. Finally, to validate the CFD results different modular hub+bearing systems were built and experimentally tested. In this way, the critical zones in terms of pressure or velocity were detected and guidelines for designing a new system were obtained.

High speed rotors on gas bearings: design and experimental characterization

Gas bearings are employed in a variety of applications from micro systems to large turbomachinery. As they are free from contaminants if supplied with clean air, gas bearings and pneumatic guide-ways are often used in food processing, textile and pharmaceutical industries. The new research works are focused on expanding the applications of gas bearings, in particular at very high speeds. Dental drills for example operate at speeds of over 500 krpm and it seems that a limit for gas bearings without cooling is 700 krpm [1]. Nevertheless in [2] a spindle with 6 mm diameter that operated at 1.2 million rpm is described.

Comparison between different supply holes configurations in gas journal bearings

Because of their precision, gas bearings are widely used for very high speed spindle applications. Compared to conventional oil bearings, gas bearings generate less heat and do not pollute the environment. Air viscosity is three orders of magnitude lower than oil, so the power dissipated in gas bearings is very low. The major disadvantage of these bearings is rotor whirl instability, which restricts the possible range of applications. Researchers have studied this problem using different methods since the 60s. Gross first applied a perturbation method to evaluate the stability of an infinitely long journal bearing (Gross & Zachmanaglou, 1961). Galerkin’s method was used by others to calculate rotor speed and mass at the stability threshold (Cheng & Pan, 1965). Lund investigated the stiffness and damping coefficients of hydrostatic gas bearing, and used these coefficients to investigate whirl instability (Lund, 1968). Wadhwa et al. adapted the perturbation method to calculate the dynamic coefficients and to study the stability of a rotor supported by orifice compensated gas bearings (Wadhwa et al., 1983). Results show that aerostatic bearings have a larger load capacity and higher stability than plain journal bearings. Han et al. proved that more circumferential supply ports result in increased stiffness coefficient but reduced damping (Han et al., 1994). Others found that orifice-compensated and shallow-pocket type hybrid gas journal bearings offer better stability than eight-orifice type bearings (Zhang & Chang, 1995). Also porous journal bearings were studied (Sun, 1975) and compared against hybrid gas bearings with multi-array entries (Su & Lie, 2006), (Heller et al., 1971). Despite the fact that damping is generally higher in porous bearings than in aerostatic bearings, the results of (Su & Lie, 2006) suggest that at high operating speeds, multi-array entry bearings are more stable than porous bearings. Other studies (Andres, 1990), (Sawcki et al., 1997), (Yoshikawa et al., 1999) considered various pressurized air compensated configurations, but very few papers analysed the influence of the number and location of entry ports. In (Su & Lie, 2003) hybrid air journal bearings with multi-array supply orifices were compared to porous bearings. One to five rows of orifices were considered. It was found that five rows of supply orifices perform as well as porous bearings, whilst supply orifice feeding has the advantage of consuming less power than porous feeding. Paper (Yang et al., 2009) compared bearing systems with double-array orifice restrictions to three and six entry

Intrinsically safe pneumatic amplifier for mechatronic systems

In this paper the study, the construction and the experimentation of new pneumatic amplifiers useful for mechatronic applications are presented