The non-axisymmetric geometry structure of the volute leads to the uneven circumferential distribution of the flow field inside centrifugal compressors. It is difficult to describe the whole flow field for few measuring points installed around the centrifugal compressor casing wall. In this paper, seventy-two static pressure measuring probes including the six circumferential position and the twelve meridional position were installed around the casing wall, and the circumferential distribution of the static pressure was compared under the different speeds at the full flow rate. Some especial circumferential distributions of the static pressure were founded through analyzing the experimental results. At the small flow rate, the circumferential distribution of the static pressure not only has the peak static pressure point induced by the volute tongue but also has the bulge phenomenon, which also appears near the design flow rate. The stall inception most likely occurs at the static pressure peak or the static pressure bulge region. In each speed, there is a flow rate corresponding to the lowest circumferential variation of the static pressure and the peak efficiency. The amplitude of the circumferential static pressure variation does not decrease with the reducing flow rate, on the contrary, the amplitude has the increasing tendency along the meridional direction. The circumferential static pressure distribution at the leading edge of the splitter blade is almost the same at different small flow rates. Meanwhile, the circumferential static pressure distribution has the two peaks phenomenon, which has the approximately 180° circumferential difference between the two peaks points.
The turbocharger, with its advantages in increasing fuel economy and reducing emission, has been widely used in internal combustion engines. Aiming to achieve both fast transient response and high boost at low engine speeds of the diesel engines, variable nozzle turbine (VNT) turbochargers are necessary to match well with the engines in various operating conditions. At different engine speeds, both the mass flow rate and expansion ratio of the exhaust gas could be controlled by changing the opening of the guide vanes to adjust the nozzle throat area. At low engine speeds, the small opening of the VNT nozzle can accelerate the exhaust gas, resulting in the increase of the compressor boost pressure. The large opening of the VNT nozzle is capable of avoiding the excessive boost pressure at high engine speeds. The high exhaust gas pressure accompanying the small opening of the guide vane at the engine braking condition leads to shock waves. Loading fluctuation on the surface of the rotor blade, in response to the shock wave at the variable guide vanes, could increase the high cycle fatigue (HCF) risk of the rotor blade significantly. In this study, the generation and weakening mechanism of the shock wave in the VNT have been investigated by adopting three guiding vanes with different span chord ratios. Numerical simulation indicates that two shock waves are produced in the geometry throat and the trailing edge of the guide vane, named throat shock wave and trailing edge shock wave, respectively. The trailing edge shock wave at mid-span area of the rotor-stator interface has the largest intensity, and it is gradually weakened towards both the rotor blade leading edge and the guide vane trailing edge. As the distance between the guiding vane and rotor blade changes, the trailing edge shock wave also varies in intensity, shape, and relative position to the blade, while the throat shock wave has no variations. Further analysis shows that the generation of the shock wave is mainly due to the excessive acceleration of the exhaust gas. Reduction of the gas expansion ratio across the variable guide vane and the channel shrinkage degree between the nozzle vane trailing edge and the rotor blade can eliminate the throat shock wave and weakens the trailing edge shock wave. As the trailing edge shock wave weakens, pressure fluctuation inside the rotor blade can be reduced, which will significantly reduce the turbine blades forced response and enhance the reliability of the VNT turbine.
Asymmetric structures of the bent inlet pipes and outlet volute are typically adopted in centrifugal compressors. By using asymmetric inlet/outlet structures, the uniformity of the compressor's internal flow field in the circumferential direction will be changed. The static pressure distribution behavior around the casing wall is significantly influenced by the coupling effect of the bent inlet pipe and outlet volute. In the present work, three compressors were numerically and experimentally investigated. One compressor had a straight inlet pipe, and the other two had bent inlet pipes. Seventy-two static pressure sensors were mounted around the casing wall to obtain the static pressure distribution at different flow rates for three rotational speeds. The results show that at high rotational speeds with large flow rate conditions, when the static pressure waves induced by the bent pipe and volute act on the same circumferential position, the casing wall static pressure will be increased at the corresponding position. Furthermore, this high static pressure will further influence the static pressure values at other circumferential positions and leads to a more nonuniform circumferential static pressure distribution. Near the design flow rate, when the high static pressure strips, which are induced by both the bent pipe and volute impact different circumferential positions, the high static pressure strip induced by the volute will be weakened. As a result, the high static pressure strip induced by the volute cannot propagate upstream into the impeller. At small flow rate under designed rotational speed, the influence of the volute tongue on the casing pressure distribution will be enhanced. At small flow rate under low rotational speed, the casing pressure distributions of the three models were almost the same because the secondary flow effect of the bent pipe diminishes as the flow rate reduces.
The flow field distribution in centrifugal compressor is significantly affected by the non-axisymmetric geometry structure of the volute. The experimental and numerical simulation methods were adopted in this work to study the compressor flow field distribution with different flow conditions. The results show that the pressure distribution in volute is characterized by the circumferential non-uniform phenomenon and the pressure fluctuation on the high static pressure zone propagates reversely to upstream, which results in the non-axisymmetric flow inside the compressor. The non-uniform level of pressure distribution in large flow condition is higher than that in small flow condition, its effect on the upstream flow field is also stronger. Additionally, the non-uniform circumferential pressure distribution in volute brings the non-axisymmetric flow at impeller outlet. In different flow conditions, the circumferential variation of the absolute flow angle at impeller outlet is also different. Meanwhile, the non-axisymmetric flow characteristics in internal impeller can be also reflected by the distribution of the mass flow. The high static pressure region of the volute corresponds to the decrease of mass flow in upstream blade channel, while the low static pressure zone of the volute corresponds to the increase of the mass flow. In small flow condition, the mass flow difference in the blade channel is bigger than that in the large flow condition.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.