A Theory on the Onset of Acoustic Resonance in a Multistage Compressor

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Xiaohua Liu ◽  
Tobias Willeke ◽  
Florian Herbst ◽  
Jun Yang ◽  
Joerg Seume
Keyword(s):  
Rotor Blade ◽  
High Speed ◽  
Flow Instability ◽  
Computational Simulation ◽  
Computational Cost ◽  
Acoustic Resonance ◽  
Excitation Source ◽  
Acoustic Excitation ◽  
Tip Leakage Flow ◽  
Suction Surface

A novel theoretical model of the internal flow field in multistage axial compressors based on an eigenvalue approach is developed, in order to predict the onset of acoustic resonance in aircraft engines. Using an example high-speed four-stage compressor, it is shown that one of the resultant frequencies is in excellent agreement with the experimental data in terms of acoustic resonance. On the basis of the computed natural frequency of the whole compression system and the measured spanwise distribution of static pressure, the location of the acoustic excitation source can be found in the third stage. Unsteady flow simulations of the full annulus of this stage reveal two criteria for acoustic excitation at the rotor-blade tip, reversed flow near the suction surface and flow impingement on the pressure surface. Additionally, a fast Fourier transform of the unsteady pressure field at the upper rotor-blade span verifies the existence of the computed unstable frequency of the oscillating tip leakage flow. Using this novel theory, which combines a theoretical calculation of flow-instability frequency of the global system with the computational simulation of a single stage, the onset mechanism and location of the excitation source of acoustic resonance in multistage turbomachinery can be explained at acceptable computational cost.

Effect of Axially Non-Uniform Rotor Tip Clearance on the Performance of a High Speed Axial Flow Compressor Stage

1994 ◽  
Author(s):  
K. Mohan ◽  
S. A. Guruprasad
Keyword(s):  
High Speed ◽  
Axial Flow ◽  
Separated Flow ◽  
Tip Clearance ◽  
Compressor Stage ◽  
Tip Leakage Flow ◽  
Suction Surface ◽  
Wall Boundary Layer ◽  
Improved Performance ◽  
Flow Compressor

An axially non-uniform type of rotor tip clearance was conceived and tried on a single stage compressor. This concept is based on the advantages of a smaller tip clearance in the front portion of the blade and a larger clearance in the rear portion which allows a higher tip leakage flow to interact with the passage secondary flow, casing wall boundary layer, separated flow on the blade suction surface and the scraping vortex, which are more prominent at the rear portion of the blade. Experimental results indicated that an axially non-uniform clearance can provide improved performance of a compressor stage. Providing the tip clearance in the compressor casing instead of at the blade tip indicated certain advantages. An ‘optimum’ value of rotor tip clearance was noticed for this compressor stage, both for axially uniform and axially non-uniform clearance.

A Theoretical Model for Flow Instability Inception in Transonic Fan/Compressors

2013 ◽  
Author(s):  
Xiaofeng Sun ◽  
Xiaohua Liu ◽  
Dakun Sun
Keyword(s):  
Theoretical Model ◽  
Flow Field ◽  
High Speed ◽  
Cfd Simulation ◽  
Flow Instability ◽  
Computational Cost ◽  
Mean Flow ◽  
Transonic Compressor ◽  
Onset Point ◽  
Transonic Fan

This paper applies a theoretical model, which has been developed recently, to calculate the flow instability inception of axial transonic fan/compressors system. After the mean flow field is computed by steady CFD simulation, a body force approach, which is a function of flow field data, is taken to represent the effects of discrete blades on the flow field and duplicate the physical sources of flow turning and loss. Further by applying appropriate boundary conditions and spectral collocation method, a group of homogeneous equations will yield from which the stability equation can be derived. The singular value decomposition method is adopted over a series of fine grids in frequency domain to solve the resultant eigenvalue problem, and the onset point of flow instability can be judged by the imaginary part of the resultant eigenvalue. The present investigation is to validate the feasibility of calculating the stall onset point for single stage transonic compressor. It is shown that this model is capable of predicting instability inception point of transonic flow with reasonable accuracy, and it is sustainable in terms of computational cost for industrial application. It is shown that this model can provide an unambiguous judgment on stall inception without numerous requirements of empirical relations of loss and deviation angle. It provides a possibility to check over-predicted stall margin during the design phase of new high speed fan/compressors. In addition, the effect of flow compressibility on the stall onset point calculation for transonic rotor is studied.

An Investigation of the IGV/Rotor Interaction in a Low Speed Axial Compressor Using DPIV

2006 ◽  
Author(s):  
Zhiqiang Gong ◽  
Zhiping Li ◽  
Maoyi Li ◽  
Yajun Lu
Keyword(s):  
Flow Field ◽  
Rotor Blade ◽  
Flow Instability ◽  
Dynamic Pressure ◽  
Axial Compressor ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Low Speed ◽  
Wide Range ◽  
Rotor Stator Interaction

IGV/rotor interaction phenomenon in axial compressors is important, because different matching states of IGV and rotor can result in significant differences in performance of the compressors. An experimental investigation of IGV/rotor interaction is performed on a one stage low speed axial compressor. The performance of the compressor is measured with the number of IGV varied within a wide range. Different IGV results in very different performance of the compressor, and the performance does not change with the number of IGV monotonously. Flow field around a rotor blade is measured using 2D Digital Particle Image Velocimetry (DPIV) and dynamic pressure probes, without IGV and with the IGV which brings the largest stall margin to the compressor. Comparison of flow fields reveals that the IGV wakes change the flow field around the rotor blade significantly. The wake of the rotor blade is weakened and its structure is changed. The rotor exit total pressure is elevated throughout the entire span. The tip leakage flow is suppressed, so relevant blockage is reduced and consequently the stable operating range of the compressor is extended. The relatively high turbulence intensity and periodic changes in flow velocity and direction brought by IGV wakes to the rotor may account for some of the observed changes in the flow field structure and the compressor performance. The flow instability and receptivity theory must be included to explain all the experimental results, and to utilize the rotor/stator interaction phenomena during the compressors design process.

Mid-Span Stall Inception in a Transonic Fan

2020 ◽  
Author(s):  
H. Verschueren ◽  
C. A. Hall ◽  
M. J. Wilson
Keyword(s):  
High Speed ◽  
Pressure Ratio ◽  
Measurement Data ◽  
Test Facility ◽  
Tip Leakage Flow ◽  
Suction Surface ◽  
Cfd Validation ◽  
Stall Inception ◽  
Stall Margin ◽  
Transonic Fan

Abstract In this paper, steady and unsteady CFD have been used to investigate stall inception for a modern low pressure ratio transonic fan. The computational results are validated against measurement data from a high-speed test facility. CFD validation was approached as a blind test case. The results shows good agreement between the experiments and computations. Stall is triggered by growth of a suction surface separation behind the shock around the mid-span of the rotor blade. As the fan is throttled the separation grows leading to increased blockage in the blade passages. At the point of instability the separation grows further, locally increasing incidence and leading to the formation of a stall cell. It is shown that changes to the tip leakage flow leave the stall inception mechanism unaffected. A computational case with a suction surface slip patch between 25–75% span shows that the reduction in blockage around the mid-span increases the stall margin by 25%. This demonstrates that for cases with mid-span initiated stall it is important to consider the flow away from the tip as well as the flow in the tip region. A redesigned fan is used to illustrate that design changes around the mid-span can be effective to improve flow range. The redesigned fan increases stall margin by 6.7% while maintaining the design point efficiency within 0.1%.

scholarly journals Event-Driven Simulation Scheme for Spiking Neural Networks Using Lookup Tables to Characterize Neuronal Dynamics

2006 ◽  
Vol 18 (12) ◽  
pp. 2959-2993 ◽  
Author(s):  
Eduardo Ros ◽  
Richard Carrillo ◽  
Eva M. Ortigosa ◽  
Boris Barbour ◽  
Rodrigo Agís
Keyword(s):  
Synaptic Plasticity ◽  
High Speed ◽  
Large Scale ◽  
Computational Cost ◽  
Brain Structures ◽  
Spike Timing ◽  
Neuronal Dynamics ◽  
Event Driven ◽  
Synaptic Dynamics

Nearly all neuronal information processing and interneuronal communication in the brain involves action potentials, or spikes, which drive the short-term synaptic dynamics of neurons, but also their long-term dynamics, via synaptic plasticity. In many brain structures, action potential activity is considered to be sparse. This sparseness of activity has been exploited to reduce the computational cost of large-scale network simulations, through the development of event-driven simulation schemes. However, existing event-driven simulations schemes use extremely simplified neuronal models. Here, we implement and evaluate critically an event-driven algorithm (ED-LUT) that uses precalculated look-up tables to characterize synaptic and neuronal dynamics. This approach enables the use of more complex (and realistic) neuronal models or data in representing the neurons, while retaining the advantage of high-speed simulation. We demonstrate the method's application for neurons containing exponential synaptic conductances, thereby implementing shunting inhibition, a phenomenon that is critical to cellular computation. We also introduce an improved two-stage event-queue algorithm, which allows the simulations to scale efficiently to highly connected networks with arbitrary propagation delays. Finally, the scheme readily accommodates implementation of synaptic plasticity mechanisms that depend on spike timing, enabling future simulations to explore issues of long-term learning and adaptation in large-scale networks.

Feasibility of High Speed Furnace Drawing of Optical Fibers

2004 ◽  
Vol 126 (5) ◽  
pp. 852-857 ◽  
Author(s):  
Xu Cheng ◽  
Yogesh Jaluria
Keyword(s):  
Optical Fibers ◽  
High Speed ◽  
Flow Instability ◽  
Fiber Quality ◽  
Domain Boundary ◽  
Operating Conditions ◽  
Furnace Temperature ◽  
Fiber Drawing ◽  
Heated Zone ◽  
Additional Information

The domain of operating conditions, in which the optical fiber-drawing process is successful, is an important consideration. Such a domain is mainly determined by the stresses acting on the fiber and by the stability of the process. This paper considers an electrical resistance furnace for fiber drawing and examines conditions for process feasibility. In actual practice, it is known that only certain ranges of furnace temperature and draw speed lead to successful fiber drawing. The results obtained here show that the length of the heated zone and the furnace temperature distribution are other important parameters that can be varied to obtain a feasible process. Physical behavior close to the boundary of the feasible domain is also studied. It is found that the iterative scheme for neck-down profile determination diverges rapidly when the draw temperature is lower than that at the acceptable domain boundary due to the lack of material flow. However, the divergence rate becomes much smaller as the temperature is brought close to the domain boundary. Additional information on the profile determination as one approaches the acceptable region is obtained. It is found that it is computationally expensive and time-consuming to locate the exact boundary of the feasible drawing domain. From the results obtained, along with practical considerations of material rupture, defect concentration, and flow instability, an optimum design of a fiber-drawing system can be obtained for the best fiber quality.

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.

Stall Inception in a High Speed Centrifugal Compressor During Speed Transients

2017 ◽  
Author(s):  
Fangyuan Lou ◽  
John C. Fabian ◽  
Nicole L. Key
Keyword(s):  
Heat Transfer ◽  
Centrifugal Compressor ◽  
High Speed ◽  
Flow Instability ◽  
Leading Edge ◽  
Fast Response ◽  
Rotating Stall ◽  
Transient Performance ◽  
Stall Inception ◽  
Pressure Transducers

The inception and evolution of rotating stall in a high-speed centrifugal compressor are characterized during speed transients. Experiments were performed in the Single Stage Centrifugal Compressor (SSCC) facility at Purdue University and include speed transients from sub-idle to full speed at different throttle settings while collecting transient performance data. Results show a substantial difference in the compressor transient performance for accelerations versus decelerations. This difference is associated with the heat transfer between the flow and the hardware. The heat transfer from the hardware to the flow during the decelerations locates the compressor operating condition closer to the surge line and results in a significant reduction in surge margin during decelerations. Additionally, data were acquired from fast-response pressure transducers along the impeller shroud, in the vaneless space, and along the diffuser passages. Two different patterns of flow instabilities, including mild surge and short-length-scale rotating stall, are observed during the decelerations. The instability starts with a small pressure perturbation at the impeller leading edge and quickly develops into a single-lobe rotating stall burst. The stall cell propagates in the direction opposite of impeller rotation at approximately one third of the rotor speed. The rotating stall bursts are observed in both the impeller and diffuser, with the largest magnitudes near the diffuser throat. Furthermore, the flow instability develops into a continuous high frequency stall and remains in the fully developed stall condition.

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