V. N. Constantinescu

Bio: V. N. Constantinescu is an academic researcher. The author has contributed to research in topics: Fluid bearing & Lubrication. The author has an hindex of 1, co-authored 1 publications receiving 90 citations.

Performance Characteristics of Worn Journal Bearings in Both Laminar and Turbulent Regimes. Part I: Steady-State Characteristics

Abstract: The effects of geometric change due to wear on the dynamic characteristics of journal bearings are determined theoretically in both laminar and turbulent regimes. The dynamic characteristics such as spring and damping coefficients and whirl onset speed of a rigid rotor supported by two identical symmetrically aligned bearings are analyzed by a semianalytical finite element method, and the numerical results for various wear depth parameters are indicated in graphical form. The geometric change due to wear has significant effects on the principal spring coefficients and on the cross-coupled damping coefficients. The whirl onset speed for a worn journal bearing whose wear depth parameter is larger than 0.3 becomes higher than the speed for a nonworn bearing.

Fluid Dynamic Foundation of Turbulent Lubrication Theory

Abstract: A critical examination of Constantinescu's theory of turbulent fluid film lubrication has been undertaken. Several of its anomalies were traced to violations of certain well-established basic phenomena in turbulent shear flows. A new approach, which is free of some of these objections, has been made. It holds promise of yielding a more consistent turbulent lubrication theory. Comparison is given on infinitely long bearing with Constantinescu's results. Contributed by the ASLE Technical Committee on Bearings and Bearing Lubrication and presented at the Annual Meeting of the American Society of Lubrication Engineers held in Chicago, Illinois, May, 1964.

Bifurcation and chaos analysis of a flexible rotor supported by turbulent long journal bearings

Abstract: For a more precise description of rotor–bearing system, a nonlinear supported model is proposed in this paper, where a linear damping, a nonlinear elastic restoring force and a turbulent lubricant flow model are assumed. The dynamics of the rotor center and bearing center are studied. The spatial displacements in the horizontal and vertical directions are considered for various non-dimensional speed ratios. The dynamic equations are solved using the Runge–Kutta method. The analysis methods employed in this study is inclusive of the dynamic trajectories of the rotor center and bearing center, Poincare maps and bifurcation diagrams. The maximum Lyapunov exponent analysis is also used to identify the onset of chaotic motion. The numerical results show that the stability of the system varies with the non-dimensional speed ratios. Specifically, it is found that the dynamic behaviors of the system include 2T-periodic, quasi-periodic and chaotic motions. The modeling results thus obtained by using the method proposed in this paper can be employed to predict the stability of the rotor–bearing system and the undesirable behavior of the rotor and bearing center can be avoided.

A Review of Grooved Dynamic Gas Bearings

Abstract: This paper offers an extensive review of publications dealing with the modeling, the design, and the experimental investigation of grooved dynamic gas-lubricated bearings. Recent years have witnessed a rise in small-scale and high-speed turbomachinery applications. Besides the well-known gas foil bearings, grooved bearings offer attractive advantages, which unveil their potential in particular at small scale due to the structural simplicity as well as satisfying predictability. This paper starts with a general background of the application of gas-lubricated bearings and introduces and compares the different gas bearing topologies. Further, the state-of-the-art modeling of grooved gas-lubricated bearings is introduced, systematically assessing the advantages and inconveniences of two major approaches, i.e., the narrow groove theory (NGT) and direct discretization method. Since the NGT method is an elegant and efficient approach to model the complex effects of periodic grooves, a critical section is dedicated to the NGT. In a second phase, different models to include additional physical phenomena such as real gas lubrication, rarefaction, or turbulence effects are reviewed. The paper concludes with a critical assessment of the state-of-the-art and indicates potential fields of research that would allow to shed more light into the understanding of these bearings, as well as with some thoughts on the integrated design methodologies of gas bearing supported rotors.