Incipient Surge Analysis in Time and Frequency Domain for Centrifugal Compressors

2021 ◽  
Author(s):  
Paolo Silvestri ◽  
Silvia Marelli ◽  
Massimo Capobianco
Keyword(s):  
Correlation Function ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Cross Correlation ◽  
Rotating Stall ◽  
Cross Correlation Function ◽  
Rate Condition ◽  
Low Mass ◽  
Processing Techniques

Abstract The use of centrifugal compressors has been increasing tremendously in the last decade as they are a key component in the present energy scenario both in the modern internal combustion engine design and in advanced cycles and innovative plant layouts as fuel cell systems. Instability phenomena limit the operating range of the whole compressor system, especially during fast transients. The target is therefore to extend the minimum flow limit in order to improve the operability of each unit, while avoiding compressor surge operation and guaranteeing safe operation. For this reason, it is necessary to develop a monitoring system capable of preventing surge and extending operating range of these machines, their performance, and reliability to allow the integration with the other plant components. The experimental investigation, carried out at the University of Genoa turbocharger test facility and presented in this work, consists of steady state and transient measurements used to characterize and identify compressor behaviour in correspondence of surge inception conditions to determine different techniques which could represent surge precursors. The data analysis concentrates on pressure and vibro-acoustic signals by applying different signal processing techniques in time and frequency domain to classify compressor operation as stable or unstable. The cross correlation function and wavelet analysis have been identified as techniques to define a precursor able to detect incipient surge conditions. Through cross correlation function analysis, it has been possible to identify the presence of propagation phenomena in the system and to evaluate how these events become more significant near an unstable low-mass flow rate condition. At low mass flow rate condition, spikes of significant amplitude are well detectable in the cross correlation function indicating the rise of significant random content in the system responses associated to the rise of incipient surge condition. Additionally, the continuous wavelet transform has been applied to operational signals to show how their time-dependent spectral structure responses can highlight the rise of unstable phenomena, not easily identifiable with traditional signal processing techniques. Exploiting its features in terms of good frequency and time resolution it allowed to identify different contents in system responses regarding phenomena which take place close to surge line and was able to detect their nature in conditions very close to deep surge ones (e.g. rotating stall with its intermitting characteristic nature). Moreover, system response was studied in high frequency range and through a demodulation technique it was found how blade pass frequency energy content change interacting with rotating stall inception, moving close to surge line. The obtained results provide an interesting diagnostic and predictive solution to detect compressor instabilities at low mass flow rate operating conditions and to prevent compressor fails.

Incipient Surge Analysis in Time and Frequency Domain for Centrifugal Compressors

2021 ◽  
Author(s):  
Paolo Silvestri ◽  
Silvia Marelli ◽  
Massimo Capobianco
Keyword(s):  
Correlation Function ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Cross Correlation ◽  
Operating Conditions ◽  
Cross Correlation Function ◽  
Centrifugal Compressors ◽  
Low Mass ◽  
Advanced Cycles

Abstract The use of centrifugal compressors has been increasing tremendously in the last decade as they are a key component in the present energy scenario both in the internal combustion engine design and in advanced cycles and innovative plant layouts. Instability phenomena limit the operating range of the whole compressor system, especially during fast transients. The target is therefore to extend the minimum flow limit in order to improve the operability of each unit, while avoiding compressor surge operation and guaranteeing safe operation. The presented experimental investigation consists of steady state and transient measurements used to characterize and identify compressor behaviour in correspondence of surge inception conditions. The data analysis concentrates on pressure and vibro-acoustic signals. The cross correlation function and wavelet analysis have been identified as techniques to define precursors able to detect incipient surge conditions. Through cross correlation function, it has been possible to find the presence of propagation phenomena and to evaluate how these events become more significant near an unstable low-mass flow rate condition. Additionally, the wavelet transform has been applied to operational signals to show how their time-dependent spectral structure responses can highlight the rise of unstable phenomena. Moreover, system response was studied in high frequency range and through a demodulation technique it was found how blade pass frequency energy content change interacting with rotating stall inception, moving close to surge. The obtained results provide an interesting diagnostic and predictive solution to detect compressor instabilities at low mass flow rate operating conditions.

scholarly journals Centrifugal Compressor Stall Control by the Application of Engineered Surface Roughness on Diffuser Shroud Using Numerical Simulations

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2033
Author(s):  
Amjid Khan ◽  
Muhammad Irfan ◽  
Usama Muhammad Niazi ◽  
Imran Shah ◽  
Stanislaw Legutko ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Centrifugal Compressor ◽  
Control Method ◽  
Flow Instability ◽  
Passive Flow Control ◽  
Passive Flow ◽  
Low Mass

Downsizing in engine size is pushing the automotive industry to operate compressors at low mass flow rate. However, the operation of turbocharger centrifugal compressor at low mass flow rate leads to fluid flow instabilities such as stall. To reduce flow instability, surface roughness is employed as a passive flow control method. This paper evaluates the effect of surface roughness on a turbocharger centrifugal compressor performance. A realistic validation of SRV2-O compressor stage designed and developed by German Aerospace Center (DLR) is achieved from comparison with the experimental data. In the first part, numerical simulations have been performed from stall to choke to study the overall performance variation at design conditions: 2.55 kg/s mass flow rate and rotational speed of 50,000 rpm. In second part, surface roughness of magnitude range 0–200 μm has been applied on the diffuser shroud to control flow instability. It was found that completely rough regime showed effective quantitative results in controlling stall phenomena, which results in increases of operating range from 16% to 18% and stall margin from 5.62% to 7.98%. Surface roughness as a passive flow control method to reduce flow instability in the diffuser section is the novelty of this research. Keeping in view the effects of surface roughness, it will help the turbocharger manufacturers to reduce the flow instabilities in the compressor with ease and improve the overall performance.

Electrostatic Sensor for Real–Time Mass Flow Rate Measurement of Particle Conveying in Pneumatic Pipeline

2012 ◽  
Author(s):  
Mohd. Fua’ad Rahmat ◽  
Wee Lee Yaw
Keyword(s):  
Real Time ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Cross Correlation ◽  
High Accuracy ◽  
Industrial Processes ◽  
Rate Measurement ◽  
Flow Rate Measurement ◽  
Controlled Flow

This paper discussed the electrostatic sensors that have been constructed for real–time mass flow rate measurement of particle conveying in a Pneumatic pipeline. Many industrial processes require continuous, smooth, and consistent delivery of solids materials with a high accuracy of controlled flow rate. This requirement can only be achieved by installing a proper measurement system. Electrostatic sensor offers the most inexpensive and simplest means of measuring solids flows in pipes. Key words: Electrostatic sensor, cross-correlation, peripheral velocity

Stall Warning Using the Rotor Tip Pressure in a Transonic Axial Compressor With Circumferential Grooves

2018 ◽  
Author(s):  
Byeung Jun Lim ◽  
Tae Choon Park ◽  
Young Seok Kang
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Single Stage ◽  
Stall Inception ◽  
Casing Treatment ◽  
Stall Warning ◽  
Transonic Axial Compressor

In this study, characteristics of stall inception in a single-stage transonic axial compressor with circumferential grooves casing treatment were investigated experimentally. Additionally, the characteristic of increasing irregularity in the pressure inside circumferential grooves as the compressor approaches the stall limit was applied to the stall warning method. Spike-type rotating stall was observed in the single-stage transonic axial compressor with smooth casing. When circumferential grooves were applied, the stall inception was suppressed and the operating point of the compressor moved to lower flow rate than the stall limit. A spike-like disturbance was developed into a rotating stall cell and then the Helmholtz perturbation was overlapped on it at N = 80%. At N = 70 %, the Helmholtz perturbation was observed first and the amplitude of the wave gradually increased as mass flow rate decreased. At N = 60%, spike type stall inceptions were observed intermittently and then developed into continuous rotating stall at lower mass flow rate. Pressure measured at the bottom of circumferential grooves showed that the level of irregularity of pressure increased as flow rate decreased. Based on the characteristic of increasing irregularity of the pressure signals inside the circumferential grooves as stall approaches, an autocorrelation technique was applied to the stall warning. This technique could be used to provide warning against stall and estimate real-time stall margins in compressors with casing treatments.

Reduced-Order Modelling of Rotating Stall

2020 ◽  
Author(s):  
Dominik Schlüter ◽  
Robert P. Grewe ◽  
Fabian Wartzek ◽  
Alexander Liefke ◽  
Jan Werner ◽  
...  
Keyword(s):  
Single Cell ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Rotational Speed ◽  
Stability Limit ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Transonic Compressor ◽  
Experimental Findings

Abstract Rotating stall is a non-axisymmetric disturbance in axial compressors arising at operating conditions beyond the stability limit of a stage. Although well-known, its driving mechanisms determining the number of stall cells and their rotational speed are still marginally understood. Numerical studies applying full-wheel 3D unsteady RANS calculations require weeks per operating point. This paper quantifies the capability of a more feasible quasi-2D approach to reproduce 3D rotating stall and related sensitivities. The first part of the paper deals with the validation of a numerical baseline the simplified model is compared to in detail. Therefore, 3D computations of a state-of-the-art transonic compressor are conducted. At steady conditions the single-passage RANS CFD matches the experimental results within an error of 1% in total pressure ratio and mass flow rate. At stalled conditions, the full-wheel URANS computation shows the same spiketype disturbance as the experiment. However, the CFD underpredicts the stalling point by approximately 7% in mass flow rate. In deep stall, the computational model correctly forecasts a single-cell rotating stall. The stall cell differs by approximately 21% in rotational speed and 18% in circumferential size from the experimental findings. As the 3D model reflects the compressor behaviour sufficiently accurate, it is considered valid for physical investigations. In the second part of the paper, the validated baseline is reduced in radial direction to a quasi-2D domain only resembling the compressor tip area. Four model variations regarding span-wise location and extent are numerically investigated. As the most promising model matches the 3D flow conditions in the rotor tip region, it correctly yields a single-cell rotating stall. The cell differs by only 7% in circumferential size from the 3D results. Due to the impeded radial migration in the quasi-2D slice, however, the cell exhibits an increased axial extent. It is assumed, that the axial expansion into the adjacent rows causes the difference in cell speed by approximately 24%. Further validation of the reduced model against experimental findings reveals, that it correctly reflects the sensitivity of circumferential cell size to flow coefficient and individual cell speed to compressor shaft speed. As the approach reduced the wall clock time by 92%, it can be used to increase the physical understanding of rotating stall at much lower costs.

Computational Fluid Dynamics Performance Estimation of Turbo Booster Vacuum Pump

2003 ◽  
Vol 125 (3) ◽  
pp. 586-589 ◽  
Author(s):  
H.-P. Cheng ◽  
C.-J. Chen , ◽  
P.-W. Cheng ,
Keyword(s):  
Fluid Dynamics ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Vacuum Pump ◽  
Performance Estimation ◽  
High Mass ◽  
Rotor Speed ◽  
Low Mass ◽  
Pump Inlet

The CFD performance estimation of turbo booster vacuum pump shows the axial vortex and back flow is evident when the mass flow rate is increased. The pressure is increased from the pump inlet to the outlet for the low mass flow rate cases. But for high mass flow rate cases, the pressure is increased until the region near the end of the rotor then decreased. The calculated inlet pressure, compression ratio, and pumping speed is increased, decreased, and decreased, respectively, when the mass flow rate is increased. The pumping speed is increased when the rotor speed is increased.

Control of Self-Excited Oscillations in Centrifugal Blowers

2007 ◽  
Author(s):  
Saad A. Ahmed
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Critical Mass ◽  
Industrial Applications ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Flow Coefficient ◽  
Flow Area ◽  
The Stability

Centrifugal compressors or blowers are widely used in many industrial applications. However, the operation of such systems is limited at low-mass flow rates by self-excited flow instabilities which could result in rotating stall or surge of the compressor. These instabilities will limit the flow range in which the compressor or the blower can operate, and will also lower their performance and efficiency. Experimental techniques were used to investigate a model of radial vaneless diffuser at stall and stall-free operating conditions. The speed of the impeller was kept constant, while the mass flow rate was reduced gradually to study the steady and unsteady operating conditions of the compressor. Additional experiments were made to investigate the effects of reducing the exit flow area on the inception of stall. The results indicate that the instability in the diffuser was successfully delayed to a lower flow coefficient when throttle rings were attached to either one or both of the diffuser walls (i.e., to reduce the diffuser exit flow area). The results also showed that an increase of the blockage ratio improves the stability of the system (i.e., the critical mass flow rate could be reduced to 50% of its value without blockage). The results indicate that the throttle rings could be an effective method to control stall in radial diffusers.

The Liftoff Properties of Dimethyl Ether Jet Diffusion Flames With Preheating

2013 ◽  
Author(s):  
Jie Zhou ◽  
Yuhua Ai ◽  
Wenjun Kong
Keyword(s):  
Ambient Temperature ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Diffusion Flames ◽  
Thermal Buoyancy ◽  
Jet Diffusion Flames ◽  
Lifted Flames ◽  
Low Mass ◽  
Jet Velocity

Liftoff properties of DME laminar axisymmetric diffusion flames were investigated experimentally with emphasis on the preheating effects. At room temperature, DME presented a different liftoff phenomenon from the non-oxygenated hydrocarbon fuels. It could not be lifted off directly by increasing the jet velocity except for far field ignition at relatively low mass flow rate. When fuel and dilution were preheated, the DME flame could be lifted off directly by increasing the jet velocity. The range of the mass flow rate of stabilized DME liftoff flames became much narrower and the liftoff height became much smaller at fuel preheating than that at ambient temperature. With the increase of the jet temperature, the DME liftoff flames exhibited as one of the following three types: stationary lifted flames, stable oscillating lifted flames and unstable oscillating lifted flames. Stationary lifted flames existed when the initial temperature was relatively low (less than 350 K). Stable oscillating lifted flames were observed at relatively high preheated temperature (about 350 K ∼ 750 K), and the trajectory of the liftoff flame base was nearly sinusoidal. Both the oscillating frequency and amplitude increased with the preheating temperature. The oscillating lifted flames were caused by thermal buoyancy effect, inertia and the instability in the inner flow. When the jet temperature exceeded 750 K, the oscillating lifted flames became unstable and easily to be blown out. The flame base of the stabilized DME liftoff flame had a tribrachial structure at both ambient temperature and elevated temperature.

scholarly journals The Effects of Diffuser Geometry on Rotating Stall Behavior

1988 ◽  
Author(s):  
M. V. Otugen ◽  
R. M. C. So ◽  
B. C. Hwang
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Critical Mass ◽  
Rotating Stall ◽  
Radius Ratio ◽  
Impeller Speed ◽  
Vaneless Diffuser ◽  
Room Condition ◽  
Inlet Opening

Experiments were carried out in a model vaneless diffuser rig to investigate the rotating stall phenomenon and its relation to diffuser geometry. The experimental rig consisted of an actual impeller which was used to deliver the flow to the vaneless diffuser. Mass flow rate through the system could be adjusted by varying the rotational speed of the impeller at a fixed inlet opening or by changing the inlet opening at a fixed impeller speed. The flow exited to room condition. As such, the rig was designed to investigate the fluid mechanics of vaneless diffuser rotating stall only. Attention was focused on the effects of diffuser width and radius on rotating stall. Three diffuser widths and three outlet radii were examined. The width-to-inlet radius ratio varied between 0.09 and 0.142 while the outlet-to-inlet radius ratio varied between 1.5 and 2. Results showed that the critical mass flow rate for the onset of rotating stall decreases with decreasing diffuser width. The critical mass flow rate is affected also by the diffuser radius ratio; larger radius ratios resulted in smaller critical mass flow rates. The ratio of the speed of rotation of the stall cell to impeller speed is found to decrease with increasing number of stall cells. This relative speed also decreases with increasing diffuser radius ratio, but it is largely independent of the diffuser width.

Delay of Unsteady Flow in a Radial Diffuser

2008 ◽  
Author(s):  
Saad A. Ahmed
Keyword(s):  
Mass Flow ◽  
Flow Rate ◽  
Flow Instability ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Flow Coefficient ◽  
Width Ratio ◽  
Flow Rates ◽  
Lower Flow ◽  
Low Mass

The operation of centrifugal compressor systems is limited at low-mass flow rates by fluid flow instabilities leading to rotating stall or surge. These instabilities limit the flow range in which the compressor can operate. They also lower the performance and efficiency of the compressor. Experiments were conducted to investigate a model of radial vaneless diffuser at stall as well as stall-free operating conditions. The speed of the impeller was kept constant at 2000 RPM, while the mass flow rate was reduced gradually to scan the steady and unsteady operating conditions of the compressor. The flow rate through the compressor was gradually decreased until flow instability is initiated at the diffuser. The flow rate was further reduced to study the characteristics of rotating stall. These measurements were reported for diffuser diameter ratios, Do/Di, of 2.0 with diffuser width ratio, b/Di, of 0.055. At lower flow rates than the critical, the rotating stall pattern with one stall cell was dominant over the pattern with two cells. In addition, the instability in the diffuser was successfully delayed to a lower flow coefficient when rough surfaces were attached to one or both sides of the diffuser with the lowest values achieved by attaching the rough surface to the shroud. Results show that the roughness has no significant effect on stall cell characteristics.

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