The effect of impeller–diffuser interactions on diffuser performance in a centrifugal compressor

Wang

Proceedings of the Institution of Mechanical Engineers, Part A:

et al. 2017

As the flow rate decreases from the design to the rotating stall condition, the enhanced impeller-diffuser interaction considerably deteriorates the flow condition at the diffuser inlet, which may trigger stall and blade vibration problems. In order to reveal the underlying mechanism and estimate the impact of the interaction within the impeller and diffuser passages, measurements using the wireless acquisition technique and high-frequency response system have been conducted on a 1.5 stage centrifugal compressor with the vaned diffuser. The details of its transient flow characteristics suggest that the effects of the impeller sweep extensively propagate in the diffuser passage. Distinctions of the shroud reversed vortex effect exist between the main and splitter blades at the impeller outlet, which initiates the predominant passage passing frequency at the diffuser inlet under small flow rate condition. In addition, the present study explains why the dominant disturbance shifts back and force between the passage passing frequency and blade passing frequency for different positions of the diffuser and flow rates. Through flow throttling, the diffuser reaction toward the impeller passage considerably strengthens due to the growing pressure potential near the convex surface of the diffuser vane, which is associated with the reversed flow.

“…Some references have mentioned the coexistence of PPF and BPF in the diffuser passage. 10,13 However, almost none of the studies have provided details to explain this phenomenon.…”

Section: Scope Of the Studymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Investigation of transient flow characteristics inside a centrifugal compressor for design and off-design conditions

Wang

Proceedings of the Institution of Mechanical Engineers, Part A:

et al. 2017

“…Polytropic efficiency is normalized by the measured maximum polytropic efficiency, and total pressure ratio is normalized by the measured maximum total pressure ratio. The experimental facility and measurement accuracy are described in Zhao et al 17 It can be seen from Figure 5 that the numerical results obtained from the two meshes are almost the same. This demonstrates that Mesh1 has reached the grid independence.…”

Section: Verification Of Cfd Resultsmentioning

confidence: 82%

Analysis of vortices and performance of different diffusers in a large mass flow coefficient centrifugal compressor

Proceedings of the Institution of Mechanical Engineers, Part A:

Liu

Wang

2017

Self Cite

An appropriate diffuser following an impeller is critical to realize a high efficiency and a wide operating range for a centrifugal compressor stage. The purpose of this study is to investigate the effect of different types of vaned diffusers on a large mass flow coefficient centrifugal compressor stage performance under different operating conditions and to reveal the loss mechanisms in the vaned diffusers. Five vaned diffusers are studied. Flow fields and vortices in a conventional diffuser and a rib diffuser are first examined. Then, vortices and flow fields in three different tandem diffusers are analyzed in detail. For the three tandem diffusers, only circumferential position of first row vanes relative to the second row vanes is different. Results show that the stage with the conventional diffuser possesses the shortest operating range. The rib diffuser has less loss due to the weaker tip leakage vortex, while its static pressure recovery coefficient is lower, and the loss in the following return part is higher. Comparison results between the three tandem diffusers imply that when the trailing edge of the first row vane is close to the pressure surface of the second row vane, the stage with the tandem diffuser has a better performance. This is ascribed to the interaction of the tip leakage vortex and suction surface vortex, which decreases the total loss, especially reduces the loss induced by the suction surface vortex. When the trailing edge of the first row vanes is close to the suction surface of the second row vane, the loss is increased since the leading edge vortex has a large strength and surrounds the suction surface vortex. Therefore, the reasonable interaction of vortices in a tandem diffuser can bring a high performance of the centrifugal compressor.

Engineering Applications of Computational Fluid Mechanics

“…For this study the 3D numerical software ANSYS-CFX (Version 17.2) was chosen. The investigation and optimization of turbines and turbo machinery blades (Teran et al, 2016;Zhang et al, 2012;Zhao et al, 2016) are typical application areas for this software. Nevertheless, examples of successful application can also be found in a wide range of cases: from wind forces on photovoltaic panels (Edgar et al, 2015) to anti-icing systems for wings (Hannat et al, 2014) or hydro power intakes (Bermúdez et al, 2017;Gabl et al, 2018).…”

Section: Generalmentioning

confidence: 99%

Design criteria for a type of asymmetric orifice in a surge tank using CFD

Gabl

Righetti

2018

An asymmetric orifice can be added to a surge tank of a hydro power plant to dampen the mass oscillation. This allows a reduction of the required volume and a more stable behavior of the overall hydraulic system. In this paper, the advantage of a typical asymmetric orifice is shown in comparison with a sharp-edged geometry with two different pipe diameters. The software ANSYS-CFX is used to investigate the influence of the individual geometry parameters (radius, length, angle at the forefront) on the local head loss coefficients and the ratio of the two flow directions. Furthermore, a coefficient is analyzed based on an equation from the literature for the sharp-edged structure, which can be used comparably for the asymmetric orifice. This allows us to reach preliminary assumptions of the losses at an early state of the design process. The following adaptation can be supported by the presented guidance for the optimization process, so that a suitable geometry for the specific boundary conditions can be found. ARTICLE HISTORY KEYWORDSControl structures; flows in pipes and nozzles; hydraulics of renewable energy systems; hydraulic structure design and management; RANS model