The instability caused by fluid leakage leads to limited performance in turbomachines. This instability may be improved by using flexible bearing supports with anisotropic stiffness. With a simplified model this effect is investigated, including the influence of many parameters. The results show that the optimum range of anistropy is strongly dependent on the parameters of the rotor-bearing system. In this paper an explanation from an energy point of view is presented to clarify the different stability behaviors with anisotropic bearing support.
Turbulent mixing of a single jet, twin jets, triple jets and multiple jets is synthetically analysed in this paper. Chung's kinetic theory of turbulence and a modified Green's function are employed to solve this problem. The probability density function of fluid elements in the velocity space of multiple plane jets and the corresponding turbulence correlations are revealed in this analysis. The calculated results are found to be in good agreement with the available experimental data. The internal physical structure of the turbulent mixing mechanism seems better understood via the kinetic theory approach. The present study provides the fundamentals for theoretical understanding of multiple-jet turbulent mixing and further application to multiple-jet turbulent combustion analysis.
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A new identification algorithm is proposed in this work to identify the parameters of mechanical joints. The method considers the whole structure as two substructures which are connected by the joints to be identified. The frequency response functions of the whole structure and substructures are used to extract the joint parameters. In contrast to the traditional methods, only a FRF matrix is needed to inverse in the proposed method. Therefore, it is possible to calculate the condition number of the FRF matrix before the identification. The condition number is defined as the ratio of the maximum singular value divided by the minimum one of a matrix. The condition number of noise contaminated FRF matrix can be used to indicate the sensitivity of the FRF matrix to measurement noise. Therefore, the condition number can be used to avoid the ill-conditioned problem by eliminating the ill-conditioned FRF in some frequency ranges before identification. The simulated results show that the proposed method can significantly improve the accuracy of identification.
A turbulent kinetic theory due to Chung and a Green's function method by Hong were employed to solve a reacting turbulent plane jet problem. An instantaneous mixing concept was used to simulate the steady state of turbulent plane jet with combustion. The probability density function description of the fluid elements in a turbulent reacting flow could properly explain the turbulent flame zone structure and the turbulent transport of heat, momentum and chemical species even under the infinitely fast reaction rate assumption. The calculated distributions of the various moments of the turbulent combustion field were found in good agreement with the available experimental data. The dynamic behaviour of combustion in the turbulent field could be better understood via the probability density function description of the present turbulent kinetic theory approach
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