scholarly journals Unstable Flow Structures Present at Different Rotational Velocities of the Centrifugal Compressor

Energies ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 4146
Author(s):  
Grzegorz Liśkiewicz ◽  
Kirill Kabalyk ◽  
Andrzej Jaeschke ◽  
Filip Grapow ◽  
Michał Kulak ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
Energy Systems ◽  
Flow Structures ◽  
Spectral Structure ◽  
Flow Conditions ◽  
Unstable Flow ◽  
Closed Type ◽  
Flow Phenomena ◽  
Surge Protection ◽  
Method Accuracy

Unstable flow structures cause inevitable energy losses in all power energy systems, including turbomachines. In this study, a set of analyses was conducted with the use of spectral maps on the pressure signals obtained from an industrial centrifugal compressor. The spectral maps provide one a detailed visualization of the flow conditions present in the machine along the performance curve and to distinguish the flow phenomena present prior to the surge. The method accuracy is especially useful in detecting the inlet recirculation. The study was conducted at four impeller rotational speeds with varying loads imposed by a valve at the outlet. At each speed, the machine experienced different stages of unstable flow conditions prior to the surge. Five main frequency peaks that appeared in all cases were identified and discussed. The surge was observed at all impeller speeds. At lower ones, however, it appeared at higher valve closures. At higher speeds, the surge was much more intense. The study has also shown that the inlet recirculation appears also for the closed-type industrial impeller. The phenomenon was present in all conditions. The higher impeller speed, the faster onset of the inlet recirculation was. This structure has a strong potential for an early instability warning because it appears in various types of impellers, has a very particular spectral structure and its positioning is very predictable. This study gives another example of the inlet recirculation universality and potential for efficient anti-surge protection.

On the Challenge of Determining the Surge Limit of Turbocharger Compressors: Part 2 – Capabilities of a Geometrically Reduced Numerical Model

2021 ◽  
Author(s):  
Dominik Paul ◽  
Johannes Ratz ◽  
Werner Eißler
Keyword(s):  
Steady State ◽  
Numerical Simulations ◽  
Research Paper ◽  
Flow Structures ◽  
Complete Model ◽  
Unstable Flow ◽  
Operation Conditions ◽  
Starting Point ◽  
Flow Phenomena ◽  
Model Setup

Abstract Steady-state numerical simulations are an essential instrument in the design process of centrifugal compressors for automotive turbochargers in an industrial environment. Although this method is state-of-the-art, the natural unsteadiness of the compressor flow especially close to stall and surge is suppressed by this kind of simulation. Unsteady numerical simulations of the complete compressor geometry are necessary to detect unstable flow structures leading to surge. As numerical costs and thus the time needed for unsteady simulations correlate with the size of numerical setup, it is not possible for industrial applications to investigate an unsteady operation condition of a centrifugal compressor. On account of that fact, it would be beneficial to reduce the model and include only the most decisive components which are responsible for the significant flow phenomena within the impeller leading to surge. The objective of this research paper is the investigation of the CFD simulation capabilities of a reduced radial compressor model for steady-state operation conditions using as a robust basis for further transient analysis. Thus, the results of a reduced model setup of one blade segment are compared to a full model setup. It is concluded that the segment model approach is capable of investigating flow phenomena within the impeller without neglecting fundamental flow structures. In addition, the consequences of the geometric reduction to a diffuser segment without volute on different flow variables are studied. This provides the guidance for further transient studies. The complete model setup, in conjunction with its validation by experimental data, serves as the starting point for this research paper. Dielenschneider et al.[1] present in the first part of the paper the procedure and a detailed comparison of complete model results with experimental analysis.

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.

Numerical Study of Off-Design Centrifugal Compressor Operation and Flow Phenomena Preceding Surge

2018 ◽  
Author(s):  
Grzegorz Liśkiewicz ◽  
Krzysztof Sobczak ◽  
Matthew Stickland ◽  
Władysław Kryłłowicz
Keyword(s):  
Experimental Data ◽  
Centrifugal Compressor ◽  
Numerical Study ◽  
Numerical Test ◽  
Sudden Onset ◽  
Rotating Stall ◽  
Flow Structures ◽  
Local Flow ◽  
Low Speed ◽  
Flow Phenomena

The paper outlines the results of a numerical analysis of a low-speed centrifugal compressor operating at design and off-design conditions. This included the analysis of surge predecessors. Surge is known to be a reason for the severe damage of compressing units and systems working with them. This phenomenon is also known to have a very quick and sudden onset. Therefore, it is important to understand the nature of flow structures that appear locally prior to the surge onset. It is generally believed that these could include: impeller rotating stall (abrupt or progressive), diffuser rotating stall, and inlet or outlet recirculation. This classification is, however, not sharp and observed flows could represent only selected features of the different phenomena. It is also not clear which structure is most likely to appear in a given system. The paper presents an exhaustive examination of flow structures observed in the case of a low-speed centrifugal compressor. Transient numerical simulations were conducted for both design and off-design conditions. The results were related to the experimental data presented in another paper. The numerical test domain consisted of blower, volute, inlet nozzle and elements of inlet and outlet channels assuring no influence of the boundary conditions on the local flow fluctuations. The analysis of the results included many factors such as: flow in the volute, flow in the impeller, flow in the diffuser and stagnation zones. The most significant flow structures appearing at pre-surge were identified as the inlet recirculation and the phenomenon representing some features of the rotating stall. The simulation, confirmed by experimental data, allowed for a better understanding of pre-surge flow structures in the case of a low-speed compressor, which is very important for the identification of early surge indicators.

Effects of Non-Axisymmetric Volute on Rotating Stall in the Vaneless Diffuser of a Centrifugal Compressor

2020 ◽  
Author(s):  
Zitian Niu ◽  
Zhenzhong Sun ◽  
Baotong Wang ◽  
Xinqian Zheng
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Stability Boundary ◽  
Rotating Stall ◽  
Evolution Process ◽  
Vaneless Diffuser ◽  
Unstable Flow ◽  
Centrifugal Compressors ◽  
Specific Location

Abstract Rotating stall is an important unstable flow phenomenon that leads to performance degradation and limits the stability boundary in centrifugal compressors. The volute is one of the sources to induce the non-axisymmetric flow in a centrifugal compressor, which has an important effect on the performance of compressors. However, the influence of volute on rotating stall is not clear. Therefore, the effects of volute on rotating stall by experimental and numerical simulation have been explored in this paper. It’s shown that one rotating stall cell generates in a specific location and disappears in another specific location of the vaneless diffuser as a result of the distorted flow field caused by the volute. Also, the cells cannot stably rotate in a whole circle. The frequency related to rotating stall captured in the experiment is 43.9% of the impeller passing frequency (IPF), while it is 44.7% of IPF captured by three-dimensional unsteady numerical simulation, which proves the accuracy of the numerical method in this study. The numerical simulation further reveals that the stall cell initialized in a specific location can be split into several cells during the evolution process. The reason for this is that the blockage in the vaneless diffuser induced by rotating stall is weakened by the mainstream from the impeller exit to make one initialized cell disperse into several ones. The volute has an important influence on the generation and evolution process of the rotating stall cells of compressors. By optimizing volute geometry to reduce the distortion of the flow field, it is expected that rotating stall can be weakened or suppressed, which is helpful to widen the operating range of centrifugal compressors.

Tip Leakage Flow Instability in a Centrifugal Compressor

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Teng Cao ◽  
Tadashi Kanzaka ◽  
Liping Xu ◽  
Tobias Brandvik
Keyword(s):  
Shear Layer ◽  
Centrifugal Compressor ◽  
Large Scale ◽  
Flow Instability ◽  
Leading Edge ◽  
Main Stream ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Unstable Flow ◽  
Tip Leakage

Abstract In this paper, an unsteady tip leakage flow phenomenon is identified and investigated in a centrifugal compressor with a vaneless diffuser at near-stall conditions. This phenomenon is associated with the inception of a rotating instability in the compressor. The study is based on numerical simulations that are supported by experimental measurements. The study confirms that the unstable flow is governed by a Kelvin–Helmholtz type instability of the shear layer formed between the main-stream flow and the tip leakage flow. The shear layer instability induces large-scale vortex roll-up and forms vortex tubes, which propagate circumferentially, resulting in measured pressure fluctuations with short wavelength and high amplitude which rotate at about half of the blade speed. The 3D vortex tube is also found to interact with the main blade leading edge, causing the reduction of the blade loading identified in the experiment. The paper also reveals that the downstream volute imposes a once-per-rev circumferential nonuniform back pressure at the impeller exit, inducing circumferential loading variation at the impeller inducer, and causing circumferential variation in the unsteady tip leakage flow.

Flow Behavior of a Centrifugal Compressor With Vaneless Diffuser at Design and Off Design Conditions

2012 ◽  
Author(s):  
Chuang Gao ◽  
Weiguang Huang ◽  
Haiqing Liu ◽  
Hongwu Zhang ◽  
Jundang Shi
Keyword(s):  
Centrifugal Compressor ◽  
Flow Behavior ◽  
Travelling Waves ◽  
Leading Edge ◽  
Pressure Oscillation ◽  
Rotating Stall ◽  
Vaneless Diffuser ◽  
Unstable Flow ◽  
Flow Recirculation ◽  
Static Performance

This paper concerns with the numerical and experimental aspects of both steady and unsteady flow behavior in a centrifugal compressor with vaneless diffuser and downstream collector. Specifically, the appearance of flow instabilities i.e., rotating stall and surge is investigated in great detail. As the first step, the static performance of both stage and component was analyzed and possible root cause of system surge was put forward based on the classic stability theory. Then the unsteady pressure data was utilized to find rotating stall and surge in frequency domain which could be classified as mild surge and deep surge. With the circumferentially installed transducers at impeller inlet, backward travelling waves during stall ramp could be observed. The modes of stall waves could be clearly identified which is caused by impeller leading edge flow recirculation at Mu = 0.96. However, for the unstable flow at Mu = 1.08, the system instability seems to be caused by reversal flow in vaneless diffuser where the pressure oscillation was strongest. Thus steady numerical simulation were performed and validated with the experimental performance data. With the help of numerical analysis, the conjectures are proved.

scholarly journals Numerical and Experimental Investigations on Optimized 3D Compressor Airfoils

2018 ◽  
Author(s):  
Jan Mihalyovics ◽  
Christian Brück ◽  
Dieter Peitsch ◽  
Ilias Vasilopoulos ◽  
Marcus Meyer
Keyword(s):  
Pressure Loss ◽  
Total Pressure ◽  
Experimental Studies ◽  
Total Pressure Loss ◽  
Design Parameters ◽  
Flow Conditions ◽  
Flow Angle ◽  
Flow Phenomena ◽  
The Impact ◽  
Stator Design

The objective of the presented work is to perform numerical and experimental studies on compressor stators. This paper presents the modification of a baseline stator design using numerical optimization resulting in a new 3D stator. The Rolls Royce in-house compressible flow solver HYDRA was employed to predict the 3D flow, solving the steady RANS equations with the Spalart-Allmaras turbulence model, and its corresponding discrete adjoint solver. The performance gradients with respect to the input design parameters were used to optimize the stator blade with respect to the total pressure loss over a prescribed incidence range, while additionally minimizing the flow deviation from the axial direction at the stator exit. Non-uniform profile boundary conditions, being derived from the experimental measurements, have been defined at the inlet of the CFD domain. The presented results show a remarkable decrease in the axial exit flow angle deviation and a minor decrease in the total pressure loss. Experiments were conducted on two compressor blade sets investigating the three-dimensional flow in an annular compressor stator cascade. Comparing the baseline flow of the 42° turning stator shows that the optimized stator design minimizes the secondary flow phenomena. The experimental investigation discusses the impact of steady flow conditions on each stator design while focusing on the comparison of the 3D optimized design to the baseline case. The flow conditions were investigated using five-hole probe pressure measurements in the wake of the blades. Furthermore, oil-flow visualization was applied to characterize flow phenomena. These experimental results are compared with the CFD calculations.

Experimental Analysis of Surge-Detection System Based on Pressure Derivatives At Part-Speed Operation

2021 ◽  
Author(s):  
Grzegorz Liskiewicz ◽  
Kirill Kabalyk ◽  
Andrzej Jaeschke ◽  
Filip Grapow ◽  
Michal Kulak ◽  
...  
Keyword(s):  
Flow Instability ◽  
Detection System ◽  
Rotating Stall ◽  
Unstable Flow ◽  
Monitoring Point ◽  
Optimal Position ◽  
Flow Disturbances ◽  
Flow Phenomena ◽  
Valve Opening ◽  
Low Mass

Abstract This paper presents tests of an anti-surge system based on pressure derivatives. The control algorithm was proven to work on different machines and with different unstable flow phenomena. Compressors are known to be affected by unstable flow conditions appearing at low mass flow rate conditions. The best known and most dangerous phenomenon is surge, which is a global instability affecting the entire impeller and regions upstream and downstream from it. A list of identified local phenomena includes among others: impeller rotating stall, diffuser rotating stall and inlet recirculation. All have a specific pressure signature that is used for early identification. The method presented in this paper is based on a control parameter named the Rate of Derivative Fluctuation (RDF). This approach involves a simple measure of flow instability that is universal and reacts to flow disturbances. RDF has been already confirmed to identify inlet recirculation and surge. The aim of this study is to conduct real-time tests of an anti-surge system implementing the RDF algorithm triggering the safety valve opening. The study confirmed the optimal position of the monitoring point. The results showed that the RDF is indeed sensitive to different types of flow instabilities appearing in different impellers, and that it provides efficient flow stability monitoring.

An initial assessment of bed destabilization risk past vegetation patches using instrumented particles

2021 ◽  
Author(s):  
Yi Xu ◽  
Valyrakis Manousos ◽  
Panagiotis Michalis
Keyword(s):  
Initial Assessment ◽  
Flow Structures ◽  
Clear Water ◽  
Flow Conditions ◽  
Flow Parameters ◽  
Water Conditions ◽  
The Mean ◽  
Acoustic Doppler Velocimetry ◽  
Patch Density ◽  
Vegetation Patches

<p>Instream vegetation may alter the mean and turbukent flow fields leading to destabilizing riverbed surface, under certain flow conditions. In particular, recent research on instream vegetation hydrodynamics and ecohydrogeomorphology has focused on how energetic flow structures and bulk flow parameters downstream a vegetation may result in riverbed destabilization. This study, demonstrated the application of a 20mm novel instrumented particle in recording entrainment rates downstream simulated vegetation patches of distinct densities, at various distances downstream these. A patch of 6mm acrilic cylinders is used to simulate the emergent vegetation having the same diameter (12cm) and different porosities or densities (void volume equal to 1.25%, 3.15%, 6.25%, 11.25%, and 17.25%). The flow velocity near the instrumented particle is recorded using acoustic Doppler velocimetry (ADV) with appropriate seeding, under clear water conditions. Preliminary results are presented with focus on the effect of vegetation patch density on the flow field and subsequent effects on particle entrainment rates and implications for bed surface destabilisation.</p>

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