Phenomena In Compressors Research Articles

Analysis of the frictional processes in piston machines

The durable and reliable work of piston compressors and pumps used in the oil and gas industry has great importance for practice. Investigation of complex problems with respect to mechanical and thermodynamic phenomena in compressors and pumps gives the opportunity to solve the problems of increasing the durability of oil and gas exploitation and transportation. Increasing the efficiency and durability of the compressor-pump stations directly depends on the correct calculations and designing of the different elements and mechanical parameters of piston machines. The problem of determining the forces affecting the crank-piston mechanisms of the piston compressors arises during the study of the friction process in the working parts, as well as the study of the oscillating movement of the moving crankshaft of this compressor. The indicated forces periodically depend on the angle, time, and rotation of the crankshaft of this compressor, as a result of which they create forces at various nodes of the piston mechanism and the shaft of the compressor machine. These specified conditions can create dangerous stresses that can cause the compressor connecting rod and crankshaft to break. In this work, in terms of its special characteristics, the forces affecting the piston compressor's lever-slider mechanism are determined by taking into account the main factors accompanying the working process. The results of the investigation can be useful for the design and exploitation of compressor stations used in the oil and gas industry.

Experimental and Computational Analysis of the Unstable Flow Structure in a Centrifugal Compressor with a Vaneless Diffuser

The unstable flow phenomena in compressors, such as stall and surge, are closely related to the efficiency and the operating region. It is indispensable to capture the unstable flow structure in compressors and understand the mechanism of flow instability at low flow rates. Cooperated with the manufacturer, an industrial centrifugal compressor with a vaneless diffuser is tested by its performance test rig and our multi-phase dynamic measurement system. Many dynamic pressure transducers are circumferentially mounted on the casing surface at seven radial locations, spanning the impeller region and the diffuser inlet region. The pressure fields from the design condition to surge are measured in details. Based on the multi-phase dynamic signals, the original location of stall occurring can be determined. Meanwhile, the information of the unstable flow structure is obtained, such as the circumferential mode and the propagating speed of stall cells. To get more details of the vortex structure, an unsteady simulation of this tested compressor is carried out. The computational result is well matched with the experimental result and further illustrates how the unstable flow structure in the impeller region gradually affects the stability of the total machine at low flow rates. The dynamic mode decomposition (DMD) method is applied to get the specific flow pattern corresponding to the stall frequency. Both experimental and computational analysis show that the flow structure at a particular radial location in the impeller region has a great impact on the stall and surge. Some differences between the computational and experimental result are also discussed. Through these two main analytical methods, an insight into the unstable flow structure in an industrial compressor is gained. The result also plays a crucial role in the guidance of the compressor stabilization techniques.

THE SURGE IDENTIFYING DEVICE IN COMPRESSORS OF AVIATION GAS-TURBINE ENGINES

This paper concentrates on the problem of identification of surge phenomena in compressors of aviation gas-turbine engines. Applicability of a surge detection method using expansion impulse response of the engine in a series of orthonormal Walsh functions is proved. As a diagnostic sign of a surge the Walsh - Fourier coefficients are accepted. The algorithm and the functional chart of the identification device of a surge are developed. Formation of classes is carried out on the basis of the analysis of a large number of experimental curves of change of parameters in workflow at a surge and normal operation of the engine.

On different calculation formulas of the pressure term in bi-phase SPH simulations

The smoothed particle hydrodynamics (SPH) method is usually expected to be an efficient numerical tool for calculating the multiphase phenomena in compressors. However, numerical instability arises around the interfaces due to the pressure inconsistency. By analyzing different formula of the pressure term under SPH approximation, we show that the frequently-used formulation (n=-1) leads to the worst performance and is thus not recommended. By contrast, we suggest the formulas n=0 and 1 in future practical SPH applications.

Quantitative description of non-equilibrium turbulent phenomena in compressors

A description of non-equilibrium turbulence in compressors is introduced by using the equation of Lagrangian velocity gradient correlation. This description is consistent to other traditional definitions in homogeneous isotropic turbulence and can be easily extended to complex anisotropic flows in compressors. We then show by post-processing in a linear cascade, that the non-equilibrium phenomena are obvious in the regions of corner separation, wake and boundary layer. Theoretical predictions show good agreement in magnitude with numerical results. We also show that the non-equilibrium phenomena cannot be eliminated even when the flow is far downstream, which indicates the importance of non-equilibrium phenomena in compressors. The aim of the present contribution is to provide a method to quantitatively describe the non-equilibrium phenomena in compressors, and to inspire future improvement on turbulence models by considering these non-negligible non-equilibrium properties in the future.

LPV model identification for gain scheduling control: An application to rotating stall and surge control problem

We approach the problem of identifying a nonlinear plant by parameterizing its dynamics as a linear parameter varying (LPV) model. The system under consideration is the Moore–Greitzer model which captures surge and stall phenomena in compressors. The control task is formulated as a problem of output regulation at various set points (stable and unstable) of the system under inputs and states constraints. We assume that inputs, outputs and scheduling parameters are measurable. It is worth pointing out that the adopted technique allows for identification of an LPV model's coefficients without the requirements of slow variations amongst set points. An example of combined identification, feedback control design and subsequent validation is presented.