Author: Yu Kwong ShumPublisher:
ISBN:
Category :
Languages : en
Pages : 114
Book Description
Impeller-diffuser Interaction in Centrifugal Compressors
Author: Yu Kwong ShumEffects of Impeller-diffuser Interaction on Centrifugal Compressor Performance
Author: Neil Paul MurrayEffects of Impeller-Diffuser Interaction on Centrifugal Compressor Performance
Author: National Aeronautics and Space Administration (NASA)Publisher: Createspace Independent Publishing Platform
ISBN: 9781720484141
Category :
Languages : en
Pages : 68
Book Description
This research program focuses on characterizing the effect of impeller-diffuser interactions in a centrifugal compressor stage on its performance using unsteady threedimensional Reynolds-averaged Navier-Stokes simulations. The computed results show that the interaction between the downstream diffuser pressure field and the impeller tip clearance flow can account for performance changes in the impeller. The magnitude of performance change due to this interaction was examined for an impeller with varying tip clearance followed by a vaned or vaneless diffuser. The impact of unsteady impeller-diffuser interaction, primarily through the impeller tip clearance flow, is reflected through a time-averaged change in impeller loss, blockage and slip. The results show that there exists a tip clearance where the beneficial effect of the impeller-diffuser interaction on the impeller performance is at a maximum. A flow feature that consists of tip flow back leakage was shown to occur at design speed for the centrifugal compressor stage. This flow phenomenon is described as tip flow that originates in one passage, flows downstream of the impeller trailing edge and then returns to upstream of the impeller trailing edge of a neighboring passage. Such a flow feature is a source of loss in the impeller. A hypothesis is put forth to show that changing the diffuser vane count and changing impeller-diffuser gap has an analogous effect on the impeller performance. The centrifugal compressor stage was analyzed using diffusers of different vane counts, producing an impeller performance trend similar to that when the impeller-diffuser gap was varied, thus supporting the hypothesis made. This has the implication that the effect impeller performance associated with changing the impeller-diffuser gap and changing diffuser vane count can be described by the non-dimensional ratio of impeller-diffuser gap to diffuser vane pitch. A procedure is proposed and developed for isolating impeller passage b
Characterization of Unsteady Loading Due to Impeller-diffuser Interaction in Centrifugal Compressors
Author: Christopher Dean LusardiPublisher:
ISBN:
Category :
Languages : en
Pages : 90
Book Description
Time dependent simulations are used to characterize the unsteady impeller blade loading due to imipeller-diffuser interaction in centrifugal compressor stages. The capability of simulations are assessed by comparing results against unsteady pressure and velocity measurements in the vaneless space. Simulations are shown to be adequate for identifying the trends of unsteady impeller blade loading with operating and design parameters. However they are not sufficient for predicting the absolute magnitude of loading unsteadiness. Errors of up to 14% exist between absolute values of flow quantities. Evidence suggests that the k - e turbulence model used is inappropriate for centrifugal compressor flow and is the significant source of these errors. The unsteady pressure profile on the blade surface is characterized as the sum of two superimposing pressure components. The first component varies monotonically along the blade chord. The second component can be interpreted as an acoustic wave propagating upstream. Both components fluctuate at the diffuser vane passing frequency, but at a different phase angle. The unsteady loading is the sum of the fluctuation amplitude of each component minus a value that is a function of the phase relationship between the pressure component fluctuations. Simulation results for different compressor designs are compared. Differences observed are primarily attributed to the amplitude of pressure fluctuation on the pressure side of the blade and the wavelength of the pressure disturbance propagating upstream. Lower pressure side pressure fluctuations are associated with a weaker pressure non-uniformity at the diffuser inlet as a result of a lower incidence angle into the diffuser. The wavelength of the pressure disturbance propagating upstream sets the domain on the blade surface in which the phase relationship between pressure component fluctuations is favorable. A longer wavelength increases the domain over which this phase relationship is such that the amplitude of unsteadiness is reduced.
CFD Investigation of Impeller-diffuser Interaction in Centrifugal Compressors
Author: Ee NgScaling of Impeller Response to Impeller-diffuser Interactions in Centrifugal Compressors
Author: David Landon TarrPublisher:
ISBN:
Category :
Languages : en
Pages : 121
Book Description
A numerical investigation has been conducted to quantify the effect of impeller-diffuser interaction on changes in impeller performance. An assessment is made of the hypothesis that the nondimensional parameter characterizing impeller performance change due to interaction is the ratio of the radial gap between the impeller trailing edge and the diffuser leading edge to the diffuser vane pitch. The time averaged results are found to show no measurable performance change with varying degrees of impeller-diffuser interaction, disproving the hypothesis. Analysis of the flow field shows that changes in loss and blockage due to interaction in the region of the blade leakage flow, which were expected to drive performance change, are negligible. The disproven hypothesis lacks parameters to relate the level of impeller passage unsteadiness to the level of performance change due to interaction, which are shown to be important. The ratio of the unsteady amplitude, of blade leakage velocity or blade loading, to the time average value appears to be a parameter capable of quantifying the impact of unsteadiness on impeller performance change.
An Investigation of Unsteady Impeller-diffuser Interactions in a Centrifugal Compressor
Author: William Barry BryanPublisher:
ISBN:
Category : Compressors
Languages : en
Pages : 352
Book Description
Forced Response of a Centrifugal Compressor Stage Due to the Impeller-diffuser Interaction
Author: Edward James WaltonPublisher:
ISBN:
Category :
Languages : en
Pages : 136
Book Description
The unsteady pressure field experienced by a centrifugal compressor stage can be dominated by of the impeller-diffuser interaction. The energy of the unsteady field, under certain aerodynamic and structural conditions, is capable of forcing the rotating impeller blades to vibrate excessively to the point of failure, better known as a high cycle fatigue (HCF) failure. This thesis seeks to identify the physical mechanisms that set the forced response amplitude of an impeller due to the impeller-diffuser interaction. The centrifugal stage researched is comprised of a stationary discrete passage diffuser and an unshrouded rotating impeller with both main and splitter blades. The forced response of two splitter blade modes are computed for a variety of structural boundary conditions and unsteady loadings to elicit the driving physical mechanisms. The findings indicate that the forced response is enhanced when the excitation frequency matches a component's natural frequency, the characteristic wavelength of the unsteady loading matches that of the structural vibration mode, the resonance occurs at high speed, and when modal displacement exists at the impeller blade's trailing edge. The findings also suggest that modal coupling of blade and disk dominant modes leads to high sensitivity of the forced response to small variations in airfoil and disk backwall thickness. Identification of blade-disk couplings are described using a simplified SAFE (Singh's Advanced Frequency Evaluation) diagram. The forced response of taut strings, Bernoulli-Euler beams, and a two mass-spring system are also utilized to elicit how the physical mechanisms act on the impeller's forced response. The Bernoulli-Euler beam model suggests that a mismatch of the forcing wavelength to the structural wavelength by 50% will reduce the forced response amplitude by at least 75%. Finally, a decision tree is proposed to assess the relative resonant risk of impeller modes to the diffuser excitation by identifying which of the physical mechanisms may be the dominant driver of the forced response.
Local Forcing Mechanisms of Centrifugal Compressor Blades Excited by Impeller-Diffuser-Interaction
Author: Carsten DegendorferAn Investigation of Unsteady Impeller-diffuser Interactions in a Centrifugal Compressor
Author: William Barry BryanPublisher:
ISBN:
Category : Compressors
Languages : en
Pages : 0
Book Description