Rotating Stall Model and Simulation of Two-Stage Centrifugal Compressors

2007 ◽  
Author(s):  
Lorenzo Scano ◽  
Gianmario L. Arnulfi
Keyword(s):  
Fluid Dynamic ◽  
Experimental Tests ◽  
Stationary Flow ◽  
Computer Code ◽  
Rotating Stall ◽  
Single Stage ◽  
Maximum Efficiency ◽  
Centrifugal Compressors ◽  
Two Stage ◽  
Multi Stage

Often turbo-compressors exhibit the maximum efficiency condition very close to the stall limit, so that it would be highly interesting to have a deep comprehension of this phenomenon. Despite the large diffusion of the multi-stage centrifugal compressors in different fields of the technology, such as natural gas pipe-lines or chemical factories, at the best authors’ knowledge, to date no theoretical model exists for rotating stall in these machines. This paper deals with a model for simulating multi-stage centrifugal compressor flow pattern during rotating stall. The model is not able to capture the stall inception, so the velocity and pressure fields are calculated throughout the machine once rotating stall has developed. The model consists of an implementation of that proposed by Moore for single-stage centrifugal compressors, so the simplifying hypotheses are: irrotational upstream fluid flow, inviscid and incompressible flow, stationary flow in the frame rotating at the same frequency of the stall cell; infinite blades are supposed both in rotors and return channel. Even if these fluid-dynamic hypotheses are really strong, it is worth of note that the reference models for rotating stall simulation in turbo-compressors (namely the Moore’s models) are based, at the present time, on them. In a previous step of this research, the authors utilized a semi-empirical approach, with phases changes between first and second diffuser based on experimental data. Now this hypothesis is removed and the model is fully analytical. The mathematical model is solved by numerical way, leaving the original semi-analytical scheme of Moore, so allowing the stall cell propagation frequency to be calculated. The computer code is written in C language for Linux operating system. It was tested in single-stage configuration with results according to Moore’s theory; for two-stage setup, obtained results appear consistent and qualitatively according with experimental tests and, unlike the single stage analysis, only fast rotation waves were found.

Structure and Propagation of Rotating Stall in a Single- and a Multi-Stage Axial Compressor

1999 ◽  
Author(s):  
H. M. Saxer-Felici ◽  
A. P. Saxer ◽  
F. Ginter ◽  
A. Inderbitzin ◽  
G. Gyarmathy
Keyword(s):  
Numerical Solutions ◽  
Equations Of Motion ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Water Model ◽  
Two Stage ◽  
Additional Information ◽  
Driving Mechanisms ◽  
Multi Stage ◽  
Stall Cells

The structure and propagation of rotating stall cells in a single- and a two-stage subsonic axial compressor is addressed in this paper using computational and experimental analysis. Unsteady solutions of the 2-D inviscid compressible (Euler) equations of motion are presented for one operating point in the fully-developed rotating stall regime for both a single- and a two-stage compressor. The inviscid assumption is verified by comparing the single-stage 2-D in viscid/compressible solution with an equivalent 2-D viscous (Navier-Stokes) result for incompressible flow. The structure of the rotating stall cell is analyzed and compared for the single- and two-stage cases. The numerical solutions are validated against experimental data consisting of flow visualization and unsteady row-by-row static pressure measurements obtained in a four-stage water model of a subsonic compressor. The CFD solutions supply a link between the observed experimental features and provide additional information on the structure of the stall flow. Based on this study. supporting assumptions regarding the driving mechanisms for the propagation of fully-developed rotating stall cells and their structure are postulated. In methodical respect the results suggest that the inviscid model is able to reproduce the essentials of the flow physics associated with the propagation of fully-developed, full-span rotating stall in a subsonic axial compressor.

scholarly journals Clinical Outcome Differences Between Single and Multi-stage Transtibial Amputations

2019 ◽  
Vol 4 (4) ◽  
pp. 2473011419S0031
Author(s):  
Daniel Moon ◽  
Kenneth Smith ◽  
Alexander Shu ◽  
Shanthan Challa ◽  
Kenneth Hunt
Keyword(s):  
Chart Review ◽  
Demographic Data ◽  
Wound Complication ◽  
Cost Of Care ◽  
Single Stage ◽  
Complication Rates ◽  
Two Stage ◽  
Primary Wound Closure ◽  
Below The Knee ◽  
Multi Stage

Category: Diabetes, Trauma, Amputation Introduction/Purpose: Transtibial amputations are often necessary when patients experience irreversible tissue damage in their lower extremities. Current amputation methods incorporate either a single-stage amputation with primary wound closure or a two-stage amputation. A two-stage amputation consists of an initial amputation, typically performed at a more distal site, followed by a second more proximal amputation with stump formalization. The reported advantages of two-staged amputations include decreased muscle retraction and the reduced spread of infection/necrosis. This has been reported to allow for reduced failure rates and lower rates of stump revision. Since two-stage amputations are associated with increased monetary costs, time spent in the hospital, and clinical resources used over single-stage amputations, establishing the differences between the clinical outcomes of both types of amputations can provide benefit-cost insight. Methods: This study was a retrospective study, so we began by pulling a query for all patients that underwent a below-the-knee amputation at our institution from January 1, 2015 through January 1, 2018. We excluded revision amputation patients and patients that suffered a traumatic amputation. We will then perform a chart review while recording demographic data, comorbidities, indication for amputation, labs and culture data if present. We will also record the final outcome of the surgery including any revision surgeries. We will collect data on total length of stay and total cost of care from the date of index surgery to the date of prosthetic fitting. For the cost analysis, a Markov model will be used, which can be incorporated with decision tree modeling to estimate the usage of healthcare resources by determining costs through the different phases of healthcare. Results: Our query returned 152 total patients, of which we estimate approximately 25% to 33% underwent a two staged amputation based on the surgeon’s typical amputation preferences. A power analysis was performed which suggested we needed 144 total patients to show a 20% anticipated absolute reduction in complication rates in two-stage amputations compared to single-stage amputations, based on a previous study. We just received the data this week and have not yet performed the full chart review. We hypothesize that two-stage amputations will be considerably more costly than single-stage but that the more involved two-stage strategy may be beneficial in certain subgroups of patients. Conclusion: While we do not yet have the chart review completed for this project, we are excited to elucidate the differences between single-stage and two-stage amputations. We anticipate having all data extracted within the next two months and a complete manuscript by the beginning of the summer. This project has the strong potential to change clinical practice of how trans-tibial amputations are performed depending on the outcome, revision rates, wound complication rates and total healthcare costs.

Implementing Full Electric Turbocharging Systems on Highly Boosted Gasoline Engines

2017 ◽  
Author(s):  
Q. Zhang ◽  
P. Lu ◽  
P. Dimitriou ◽  
S. Akehurst ◽  
C. Copeland ◽  
...  
Keyword(s):  
Internal Combustion Engines ◽  
Gasoline Engine ◽  
Negative Impact ◽  
Combustion Engine ◽  
Power Level ◽  
Internal Combustion ◽  
Single Stage ◽  
Maximum Efficiency ◽  
Two Stage ◽  
Waste Energy

To secure the highly challenging 2°C climate change limit, the automotive sector is expected to further improve the efficiency of the internal combustion engines. Over the past decade, internal combustion engine downsizing through turbocharging has become one of the major solutions that the industry has offered to fulfil its carbon commitment. Although the various new turbocharging technologies has changed the sluggish image of conventional turbocharged engines, the turbocharger system is far from perfect. From the perspective of engine energy flow, the copious amount of waste energy is habitually harvested by the turbine with low efficiency, subsequently the turbine power transmitted to the compressor is used solely to charge the engine. When this power for charging is excessive for the set engine operating condition, it either is consumed by throttling or is directly discharged through the wastegate, both as a pure enthalpy loss. To more efficiently harness the waste energy without deteriorating other engine performance parameters, a full electric turbocharging technology is proposed by Aeristech Ltd. The system is composed of an electric turbo generator and an electric compressor connected only through electrical system. Without the constraint of a mechanical turboshaft, the compressor and the turbine can be operated at different speeds. The electrically driven compressor can be free floating when boost is not required and the motor can provide the boost promptly only when higher load is requested. Meanwhile, the electric turbine can be controlled by the generator to operate at any set speed, allowing maximum efficiency for energy harvesting. This paper presents a simulation study of the capability of the decoupled eTurbocharging system to charge a highly boosted 2 litre gasoline engine. The single stage eTurbocharger configuration and the eTurbocharger plus a mechanical turbocharger configuration were evaluated and compared. The simulation results have revealed that the two stage eTurbocharging system has the potential to reduce CO2 emission in the proximity of 1 percent in different drive cycles compared to conventional wastegate turbocharger and the benefit would be much higher for future real world driving cycle. The single stage configuration was shown to be impractical in that the power level of the turbine generator will not only limit the engine power output, but also have negative impact on the system design, cooling and cost implied. Meanwhile, the two stage configuration where the eCompressor acts as a supplementary boost device at low end and transient device came out as a better solution with overall advantage in manageable power level, system efficiency, transient response and implied cost.

scholarly journals The Influence of Adjustable Inlet Guide Vanes on the Performance of Multi-Stage Industrial Centrifugal Compressors

1992 ◽  
Author(s):  
Klaus Lüdtke
Keyword(s):  
Molecular Weight ◽  
Mach Number ◽  
Power Consumption ◽  
Single Stage ◽  
Centrifugal Compressors ◽  
Guide Vanes ◽  
Inlet Guide Vanes ◽  
Multi Stage ◽  
Centrifugal Process ◽  
Influential Parameters

Not only single-stage but also multi-stage centrifugal process compressors are often equipped with one row of adjustable Inlet guide vanes before the first stage. The question, frequently asked by the rotating equipment purchaser is whether such an expensive component is justified for multi-stage centrifugal compressors, since it effects first stage head only. Does or does it not improve turn-down or power consumption in comparison with ordinary butterfly valva suction throttling? The paper examines if and to what degree the favorable turn-down and part-load power consumption of IGV-equipped single-stage machines can be transferred to multi-stage compressors. An intuitive answer of-course is: the lower the number of stages, the more advantageous is the IGV-equipped compressor. There are however other influential parameters like molecular weight of the gas, Mach number, number of intercoolers and others. In contrast to axial and integral gear compressors centrifugal single-shaft compressors cannot be equipped with adjustable IGV’s before each stage due to an extreme lack of interstage space dictated by rotordynamic requirements. The maximum number of IGV’s is two for back-to-back arranged centrifugal impellers.

Experimental Investigation of Rotating Instabilities in a Two-Stage Centrifugal Compressor With Vaneless Diffuser

2001 ◽  
Author(s):  
Vladimir V. Golubev
Keyword(s):  
Experimental Investigation ◽  
Centrifugal Compressor ◽  
Pressure Fluctuations ◽  
Rotating Stall ◽  
Sensitive Area ◽  
Flow Conditions ◽  
Vaneless Diffuser ◽  
Unstable Flow ◽  
Two Stage ◽  
Multi Stage

Abstract This paper examines unsteady response of an experimental two-stage centrifugal compressor with vaneless diffusers. A thorough investigation of pressure fluctuations along the compressor channel is carried out in order to examine the onset of unstable flow conditions. Rotating stall structures are localized, with special attention paid to identifying the most sensitive area of the multi-stage compressor channel which may serve as a precursor to unstable compressor operation. It is shown that both stages may develop rotating stall structures simultaneously, however the 2nd stage tends to destabilize first and reveals higher magnitudes of the unsteady response.

The anaerobic treatment of a ligno-cellulosic substrate offering little natural pH buffering capacity

1998 ◽  
Vol 38 (4-5) ◽  
pp. 29-35 ◽  
Author(s):  
C. J. Banks ◽  
P. N. Humphreys
Keyword(s):  
Ph Control ◽  
Anaerobic Treatment ◽  
Buffering Capacity ◽  
Single Stage ◽  
Stable Operation ◽  
Reactor Performance ◽  
Two Stage ◽  
Ph Buffering ◽  
Stage System ◽  
The Stability

The stability and operational performance of single stage digestion with and without liquor recycle and two stage digestion were assessed using a mixture of paper and wood as the digestion substrate. Attempts to maintain stable digestion in both single stage reactors were unsuccessful due to the inherently low natural buffering capacity exhibited; this resulted in a rapid souring of the reactor due to unbuffered volatile fatty acid (VFA) accumulation. The use of lime to control pH was unsatisfactory due to interference with the carbonate/bicarbonate equilibrium resulting in wide oscillations in the control parameter. The two stage system overcame the pH stability problems allowing stable operation for a period of 200 days without any requirement for pH control; this was attributed to the rapid flushing of VFA from the first stage reactor into the second stage, where efficient conversion to methane was established. Reactor performance was judged to be satisfactory with the breakdown of 53% of influent volatile solids. It was concluded that the reactor configuration of the two stage system offers the potential for the treatment of cellulosic wastes with a sub-optimal carbon to nitrogen ratio for conventional digestion.

scholarly journals Research on aerodynamic characteristics of two-stage axial micro air turbine spindle for small parts machining

2020 ◽  
Vol 12 (12) ◽  
pp. 168781402098437
Author(s):  
Liu Jiang ◽  
Guo Zhiping ◽  
Miao Shujing ◽  
He Xiangxin ◽  
Zhu Xinyu
Keyword(s):  
High Speed ◽  
Aerodynamic Characteristics ◽  
Maximum Efficiency ◽  
Two Stage ◽  
Output Torque ◽  
Air Turbine ◽  
Solid Foundation ◽  
Computational Fluid Dynamics Cfd ◽  
Micro Machine ◽  
Small Parts

In order to meet the requirements of output torque, efficiency and compact shape of micro-spindles for small parts machining, a two-stage axial micro air turbine spindle with an axial inlet and outlet is proposed. Based on the k-ω turbulence model of SST, the flow field and operation characteristics of the two-stage axial micro air turbine spindle were studied using computational fluid dynamics (CFD) combined with an experimental study. We obtained the air turbine spindle under different working conditions of the loss and torque characteristics. When the inlet pressure was 300 KPa, the output speed of the two-stage turbine was 100,000 rpm, 9% higher than that of a single-stage turbine output torque. The total torque reached 6.39 N·mm, and the maximum efficiency of the turbine and the spindle were 42.2% and 32.3%, respectively. Through the research on the innovative structure of the two-stage axial micro air turbine spindle, the overall performance of the principle prototype has been significantly improved and the problems of insufficient output torque and low working efficiency in high-speed micro-machining can be solved practically, which laid a solid foundation for improving the machining efficiency of small parts and reducing the size of micro machine tool.

Numerical assessment on the performance of variable area single- and two-stage ejectors: A comparative study

2021 ◽  
pp. 095440892110331
Author(s):  
Anil Kumar ◽  
Virendra Kumar ◽  
PMV Subbarao ◽  
Surendra K Yadav ◽  
Gaurav Singhal
Keyword(s):  
Change Theory ◽  
Single Stage ◽  
Two Stage ◽  
Entrainment Ratio ◽  
Ansys Fluent ◽  
One Dimensional ◽  
Flow Parameters ◽  
Constant Rate ◽  
Numerical Assessment ◽  
The One

The two-stage ejector has been suggested to replace the single-stage ejector geometrical configuration better to utilize the discharge flow’s redundant momentum to induce secondary flow. In this study, the one-dimensional gas dynamic constant rate of momentum change theory has been utilized to model a two-stage ejector along with a single-stage ejector. The proposed theory has been utilized in the computation of geometry and flow parameters of both the ejectors. The commercial computational fluid dynamics tool ANSYS-Fluent 14.0 has been utilized to predict performance and visualize the flow. The performance in terms of entrainment ratio has been compared under on- design and off-design conditions. The result shows that the two-stage ejector configuration has improved (≈57%) entrainment capacity than the single-stage ejector under the on-design condition.

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