Experience in Full-Load Testing of Natural Gas Centrifugal Compressors for Rotordynamics Improvements

1997 ◽  
Vol 119 (4) ◽  
pp. 934-941 ◽  
Author(s):  
A. Gelin ◽  
J.-M. Pugnet ◽  
D. Bolusset ◽  
P. Friez
Keyword(s):  
Natural Gas ◽  
Stability Limit ◽  
Rotating Stall ◽  
Low Flow ◽  
Load Testing ◽  
Centrifugal Compressors ◽  
High Rotational Speed ◽  
Full Load ◽  
Load Tests ◽  
Gas Seals

During full-load shop tests under natural gas, two multistage centrifugal compressors exhibited subsynchronous vibrations. Both of them are low-flow, high-pressure, high rotational speed compressors, and are fitted with tilting pad bearings and dry gas seals. A rotating stall problem was first eliminated by a modification of the diffuser geometry. Then, aerodynamic excitations caused the rotors to operate at their stability limit, and high vibration levels were observed at the first natural frequency. A complete rotordynamics analysis was performed in order to model precisely all the fluid–structure interactions. Modifications of the rotor designs were implemented, consisting in optimizing conveniently the bearing pads, replacing the toothed labyrinth seals of the balance pistons by damping honeycomb seals, fitting them with improved shunt hole systems. In addition, the dry gas seals were found to have been damaged, due to thermal effects, and further modifications were implemented to eliminate this problem. Final full load tests demonstrated a satisfactory behavior of both centrifugal compressors.

Experience in Full Load Testing Natural Gas Centrifugal Compressors for Rotordynamics Improvements

1996 ◽  
Author(s):  
Alain Gelin ◽  
Jean-Marc Pugnet ◽  
Daniel Bolusset ◽  
Patrick Friez
Keyword(s):  
Natural Gas ◽  
Stability Limit ◽  
Rotating Stall ◽  
Low Flow ◽  
Load Testing ◽  
Centrifugal Compressors ◽  
High Rotational Speed ◽  
Full Load ◽  
Load Tests ◽  
Gas Seals

During full load shop tests under natural gas, two multistage centrifugal compressors exhibited subsynchronous vibrations. Both of them are low flow, high pressure, high rotational speed compressors, and are fitted with tilting pad bearings, and dry gas seals. A rotating stall problem was firstly eliminated by a modification of the diffuser geometry. Then, aerodynamic excitations caused the rotors to operate at their stability limit, and high vibration levels were observed at the first natural frequency. A complete rotordynamics analysis was performed in order to model precisely all the fluid-structure interactions. Modifications of the rotor designs were implemented, consisting in optimizing conveniently the bearing pads, replacing the toothed labyrinth seals of the balance pistons by damping honeycomb seals, fitting them with improved shunt hole systems. In addition, the dry gas seals were found to have been damaged, due to thermal effects, and further modifications were implemented to eliminate this problem. Final full load tests demonstrated a satisfactory behaviour of both centrifugal compressors.

Criteria for the Stability Limit Prediction of High Speed Centrifugal Compressors With Vaneless Diffuser: Part I — Flow Structure Analysis

2020 ◽  
Author(s):  
Carlo Cravero ◽  
Davide Marsano
Keyword(s):  
Rotational Speed ◽  
High Speed ◽  
Stability Limit ◽  
Vaneless Diffuser ◽  
Centrifugal Compressors ◽  
Vaned Diffuser ◽  
High Rotational Speed ◽  
Lower Accuracy ◽  
The Stability ◽  
Computational Resources

Abstract High-speed centrifugal compressor requirements include a wide operating range between choking and stall especially for turbocharging applications. The prediction of the stability limit at different speeds is still challenging. In literature, several studies have been published on the phenomena that trigger the compressor instability. However, a comprehensive analysis of criteria that can be used in the first steps of centrifugal compressors design to predict the stability limit is still missing. In previous work the authors have already presented a criterion, so called “Stability Parameter”, to predict the surge line of centrifugal compressors based on a simplified CFD approach that does not require excessive computational resources and that can be efficiently used in the preliminary design phases. The above methodology has demonstrated its accuracy for centrifugal compressors with vaned diffuser, but a lower accuracy has been detected for vaneless diffusers. Before proceeding to identify additional criteria focused on compressors with vaneless diffuser, an in-depth fluid dynamics analysis has been necessary. This analysis has been also carried out through fully 3D unsteady simulations to allow identifying the real phenomena linked to the trigger of the instability of centrifugal compressors. It has been found how these phenomena are strongly related to the rotational speed, in particular have been shown the key role of the volute at high rotational speed.

scholarly journals ЗБІЛЬШЕННЯ ДІАПАЗОНУ СТІЙКОЇ РОБОТИ СТУПЕНЯ ВІДЦЕНТРОВОГО КОМПРЕСОРА З БЕЗЛОПАТКОВИМ ДИФУЗОРОМ

2019 ◽  
pp. 4-9
Author(s):  
Микола Васильович Калінкевич ◽  
Микола Іванович Радченко
Keyword(s):  
Mathematical Model ◽  
Gas Injection ◽  
Rotating Stall ◽  
Low Flow ◽  
Stable Operation ◽  
Vaneless Diffuser ◽  
Centrifugal Compressors ◽  
Flow Separation Control ◽  
Flow Part ◽  
Vaneless Diffusers

Centrifugal compressors often operate at different capacities, so it is important to ensure their stable operation over a wide flow range. Stages with vaneless diffusers have several advantages compared to stages with other types of diffusers: they are more technologically advanced to manufacture, and more uniform pressure distribution behind the impeller improves the dynamics of the rotor. At low flows, due to the occurrence of a rotating stall and surge, the efficiency of stages with vaneless diffusers rapidly decreases. The occurrence of unstable operating modes of centrifugal compressor stages at low flow rates is associated with the appearance of developed backflows in the flow part. To expand the range of stable operation of the stages, it is necessary to use methods of flow separation control. Separation of the flow can be controlled either by special profiling the flow part channels or by actively influencing the flow, for example, by injecting gas. To solve this problem, a mathematical model of the gas flow in a vaneless diffuser with gas injection is developed. The characteristics and parameters of the flow in the vaneless diffusers with various meridional profiles with and without injecting gas were calculated. A comparison of the calculated and experimental characteristics of the vaneless diffusers and flow parameters in diffusers with different geometries and with different injection modes confirms the adequacy of the mathematical model. Investigations have confirmed the possibility of improving the characteristics of the stages of centrifugal compressors through the use of vaneless diffusers and diffusers with gas injection. Gas injection diffusers extend the stable operation range of the stages. The use of gas injection in a vaneless diffuser allows reducing the power consumption during antisurge control in comparison with the widespread bypass suction system at the entrance to the impeller

Excitation Mechanism for Standing Stall of Centrifugal Compressors

1998 ◽  
Author(s):  
Y. N. Chen ◽  
D. Hagelstein ◽  
U. Haupt ◽  
M. Rautenberg
Keyword(s):  
Pressure Wave ◽  
Reverse Flow ◽  
Incidence Angle ◽  
Leading Edge ◽  
Forward Direction ◽  
Rotating Stall ◽  
Low Flow ◽  
Experimental Investigations ◽  
Centrifugal Compressors ◽  
Suction Surface

The standing stall of the centrifugal compressors appears with pulsating or switching pattern at operating points slightly away from the stall line. It is a weak form of the rotating stall and stands still in the absolute frame. The reverse flow of the compressed warm fluid travelling from the impeller’s outlet along the shroud surface towards the inlet is not yet powerful enough to generate rotating stall. The experimental investigations revealed that in the low-flow-rate off-design region, the inlet flow to the impeller has a large positive incidence angle. Nose bubbles are formed on the suction surface of the blade after the leading edge. Once the reverse flow as a pressure wave reaches the inlet of the blades, the nose bubble is stagnated to an enlarged size. The corresponding disturbance sends a rarefaction wave in the forward direction into the impeller. This wave of cool fluid meets the reverse pressure wave of the warm fluid at a circular front around the circumference of the impeller. Since this circular front has a weak baroclinicity, it cannot develop into Rossby waves which initiate the rotating stall. Instead it will either pulsate concentrically or switch linearly. We then experience a standing stall with the corresponding pattern.

scholarly journals A Numerical Study on the Combustion Process and Emission Characteristics of a Natural Gas-Diesel Dual-Fuel Marine Engine at Full Load

Energies ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1342
Author(s):  
Van Chien Pham ◽  
Jae-Hyuk Choi ◽  
Beom-Seok Rho ◽  
Jun-Soo Kim ◽  
Kyunam Park ◽  
...  
Keyword(s):  
Natural Gas ◽  
Combustion Process ◽  
Simulation Software ◽  
Dual Fuel ◽  
Injection Timing ◽  
Emission Characteristics ◽  
Cylinder Pressure ◽  
Marine Engine ◽  
Full Load ◽  
Simulation Results

This paper presents research on the combustion and emission characteristics of a four-stroke Natural gas–Diesel dual-fuel marine engine at full load. The AVL FIRE R2018a (AVL List GmbH, Graz, Austria) simulation software was used to conduct three-dimensional simulations of the combustion process and emission formations inside the engine cylinder in both diesel and dual-fuel mode to analyze the in-cylinder pressure, temperature, and emission characteristics. The simulation results were then compared and showed a good agreement with the measured values reported in the engine’s shop test technical data. The simulation results showed reductions in the in-cylinder pressure and temperature peaks by 1.7% and 6.75%, while NO, soot, CO, and CO2 emissions were reduced up to 96%, 96%, 86%, and 15.9%, respectively, in the dual-fuel mode in comparison with the diesel mode. The results also show better and more uniform combustion at the late stage of the combustions inside the cylinder when operating the engine in the dual-fuel mode. Analyzing the emission characteristics and the engine performance when the injection timing varies shows that, operating the engine in the dual-fuel mode with an injection timing of 12 crank angle degrees before the top dead center is the best solution to reduce emissions while keeping the optimal engine power.

Investigation of Grouted Coupler Connection Details for Accelerated Bridge Construction

2021 ◽  
pp. 036119812199939
Author(s):  
Brent Phares ◽  
Yoon-Si Lee ◽  
Travis K. Hosteng ◽  
Jim Nelson
Keyword(s):  
Crack Width ◽  
High Performance ◽  
Static Load ◽  
High Performance Concrete ◽  
Precast Concrete ◽  
Chloride Penetration ◽  
Load Testing ◽  
Test And Evaluation ◽  
Load Tests ◽  
Precast Elements

This paper presents a laboratory investigation on the performance of grouted rebar couplers with the connection details similar to those utilized on the precast concrete elements of the Keg Creek Bridge on US 6 in Iowa. The testing program consisted of a series of static load tests, a fatigue test, and evaluation of the chloride penetration resistance of laboratory specimens. The goal of this testing was to evaluate the ability of the grouted rebar couplers to develop flexural capacity at the joint between the precast elements as well as the durability of the connection. For structural load testing, seven full-scale specimens, each with #14 epoxy-coated rebars spliced by epoxy-coated grouted couplers, were fabricated and tested in three different loading cases: four-point bending, axial tension plus bending, and a cyclic test of the system in bending. The static load testing demonstrated that the applied axial load had a minimal effect on the formation of cracks and overall performance of the connection. When ultra-high performance concrete was used as a bedding grout, the initiation of crack was slightly delayed but no considerable improvement was observed in the magnitude of the crack width during loading or the crack closure on unloading. The results of the seventh specimen, tested in fatigue to 1 million cycles, showed little global displacement and crack width throughout the test, neither of which expanded measurably. No evidence of moisture or chloride penetration was detected at the grouted joint during the 6-month monitoring.

Roles of vanes in diffuser on stability of centrifugal compressor

2019 ◽  
Vol 233 (14) ◽  
pp. 5380-5392
Author(s):  
Wangzhi Zou ◽  
Xiao He ◽  
Wenchao Zhang ◽  
Zitian Niu ◽  
Xinqian Zheng
Keyword(s):  
High Pressure ◽  
Centrifugal Compressor ◽  
Dynamic Pressure ◽  
Pressure Ratio ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Centrifugal Compressors ◽  
Compression System ◽  
The Stability ◽  
Rotating Instability

The stability considerations of centrifugal compressors become increasingly severe with the high pressure ratios, especially in aero-engines. Diffuser is the major subcomponent of centrifugal compressor, and its performance greatly influences the stability of compressor. This paper experimentally investigates the roles of vanes in diffuser on component instability and compression system instability. High pressure ratio centrifugal compressors with and without vanes in diffuser are tested and analyzed. Rig tests are carried out to obtain the compressor performance map. Dynamic pressure measurements and relevant Fourier analysis are performed to identify complex instability phenomena in the time domain and frequency domain, including rotating instability, stall, and surge. For component instability, vanes in diffuser are capable of suppressing the emergence of rotating stall in the diffuser at full speeds, but barely affect the characteristics of rotating instability in the impeller at low and middle speeds. For compression system instability, it is shown that the use of vanes in diffuser can effectively postpone the occurrence of compression system surge at full speeds. According to the experimental results and the one-dimensional flow theory, vanes in diffuser turn the diffuser pressure rise slope more negative and thus improve the stability of compressor stage, which means lower surge mass flow rate.

Backward Traveling Rotating Stall Waves in Centrifugal Compressors

2002 ◽  
Author(s):  
Z. S. Spakovsky
Keyword(s):  
Mass Flow ◽  
Centrifugal Compressor ◽  
First Principles ◽  
Rotating Stall ◽  
Air Injection ◽  
System Stability ◽  
Centrifugal Compressors ◽  
Injection Scheme ◽  
Surge Margin ◽  
Low Order

Rotating stall waves that travel against the direction of rotor rotation are reported for the first time and a new, low-order analytical approach to model centrifugal compressor stability is introduced. The model is capable of dealing with unsteady radially swirling flows and the dynamic effects of impeller-diffuser component interaction as it occurs in centrifugal compression systems. A simple coupling criterion is developed from first principles to explain the interaction mechanism important for system stability. The model findings together with experimental data explain the mechanism for first-ever observed backward traveling rotating stall in centrifugal compressors with vaned diffusers. Based on the low-order model predictions, an air injection scheme between the impeller and the vaned diffuser is designed for the NASA Glenn CC3 high-speed centrifugal compressor. The steady air injection experiments show an increase of 25% in surge-margin with an injection mass flow of 0.5% of the compressor mass flow. In addition, it is experimentally demonstrated that this injection scheme is robust to impeller tip-clearance effects and that a reduced number of injectors can be applied for similar gains in surge-margin. The results presented in this paper firmly establish the connection between the experimentally observed dynamic phenomena in the NASA CC3 centrifugal compressor and a first principles based coupling criterion. In addition, guidelines are given for the design of centrifugal compressors with enhanced stability.

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