Three-dimensional flow field downstream of an embedded stator in a multistage axial flow compressor: Part 1: Steady and unsteady flow fields

Prato, J.; Lakshminarayana, B.; Suryavamshi, N.

doi:10.1243/0957650011538532

Cited by 7 publications

(4 citation statements)

References 15 publications

(30 reference statements)

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“…However, it is not unusual to consider even a lower number of samples: Read and Elder [3] employed 43 samples (8.95 points per degree); Mailach and Vogeler [4], 49 samples (8.57); Velarde-Suárez el al. [5], 32 samples (0.71) and Prato et al [6], 20 samples (4.11); or more recently, Lepicovsky [7], introducing 16 samples to obtain 625 points for a complete revolution (1.73).…”

Section: -Introductionmentioning

confidence: 99%

Converged statistics for time-resolved measurements in low-speed axial fans using high-frequency response probes

Oro

Díaz

Lastra

et al. 2014

Experimental Thermal and Fluid Science

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Fast-response probes in multistage turbomachinery are typically used to measure unsteady flows and turbulence in a number of traverse locations throughout the machine (rotor-stator interregions, inlet and outlet sections, tip clearance gaps…). When used intensively, they provide complete information of time-resolved flow structures, including wake patterns, wake mixing, wake-wake and rotor-wake interactions or turbulence transport in 2D planes and even 3D pictures if the raw signals are post-processed accurately. The segregation between deterministic, unsteady features and turbulent scales is essential to understand the unsteady mechanisms responsible for the energy transfer and requires an accurate selection of the sampling frequencies and the total length of the measured traces to assure a valid statistical reduction. Similar considerations must be made if they are filtered in a frequency basis (for example, filtering low-scale turbulence or extracting only BPF components), employing welldesigned periodograms or power spectra with minimum scatter and large periods of time integration. This work presents the effect of number of periods (ensembles), resolution in which the averaged periods are reconstructed and turbulence intensity on the experimental accuracy of ensemble-averaged measurements in low-speed axial fans using fast-response probes. In particular, the statistical analysis is established in terms of convergence (residuals) between timeresolved traces retrieved using different sampling frequencies and number of total samples. The possible effects of three-dimensionality, the measured regions (hub, tip, midspan) or the sensibility to turbulence levels is also explored. A technique to quantify the convergence of the phase-locked averaging (PLA) processes is applied to a low-speed axial fan, with twin configurations of rotor-stator and stator-rotor arrangements. As a starting point, a concise survey of usual practices employed by other authors in the literature for axial fans and compressors is firstly reviewed, in order to identify fundamental parameters and values typically adopted to guarantee convergence. Finally, typical requirements are given as a function of the variable analyzed, the wake pattern to be described or the global disorder of the flow structures inside axial flow fans.

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Section: -Introductionmentioning

confidence: 99%

Converged statistics for time-resolved measurements in low-speed axial fans using high-frequency response probes

Oro

Díaz

Lastra

et al. 2014

Experimental Thermal and Fluid Science

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“…The assessment of these periodic events over the time-averaged flow is extremely valuable, deserving major research efforts. Hence, in recent years a number of investigations have been focused towards the understanding of this unsteadiness and its impact on the global performance of both compressors and turbines [14][15][16][17]. Nowadays, current trends in design of axial turbomachinery takes into account the averaged influence of unsteady flow sources in the prototype's figures of merit.…”

Section: Introductionmentioning

confidence: 99%

Non-deterministic kinetic energy within the rotor wakes and boundary layers of low-speed axial fans: frequency-based decomposition of unforced unsteadiness and turbulence

Oro

Díaz

Marigorta

2009

Journal of Turbulence

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A detailed analysis of the non-deterministic scales of the flow in low-speed axial turbomachinery has revealed the presence of significant large-scales unsteadiness, with periodic features different to the blade passing frequency (BPF), which are superimposed to the turbulent structures. Introducing a frequency-based decomposition, this additional component has been segregated from turbulent phenomena so the total unsteadiness has been found to be contributed by three components: forced unsteadiness (deterministic scales), unforced unsteadiness (large-scale unsteadiness) and turbulence (small-scale randomness). Dual hot-wire anemometry has been employed intensively within the stage of a low-speed axial fan to provide a valuable experimental database, where the phaselocked averaging technique has been applied to retrieve time-resolved fluctuations and isolate the non-deterministic contribution. The present investigation shows that the presence of the unforced component is mainly related to instabilities of the rotor wakes and tip vortex structures, as well as wake-wake interactions. Moreover, typical eddies size of this component distribute their energy within the frequency range that is containing an 80% of the total unsteady kinetic energy. As a consequence, it is expected that LES schemes with accurate spatial discretizations may address this component within the resolved scales of the filter, while unsteady RANS modelling could require additional modelling of the unforced mechanisms. In addition, maps and radial distributions of every component illustrate that major flow patterns are identifiable in all of them, due to the redistribution of all-range scales throughout the energy cascade. Turbulent and forced mechanisms present important variations with the operating conditions, while the unforced component is barely affected by flow rate variations. It is shown that typical values of unforced unsteadiness reach up to a 20% of the total unsteady energy, even for nominal conditions at midspan of the rotor passage. Higher levels of all the components are found towards tip and hub boundary layers, as the total unsteadiness is reinforced by massive flow separations, tip blockages and major flow disturbances.

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“…2 The losses here are mainly due to the endwall boundary layers and blockage. Prato et al 3 presented a comprehensive investigation of the three-dimensional flow in a multistage axial flow compressor. The results indicated that major blockage in the stator hub endwall is caused by leakage flow and its possible subsequent roll-up into a vortex.…”

Section: Introductionmentioning

confidence: 99%

Investigation of endwall treatment and shock control in a five-stage axial compressor

Yang

Zheng

2017

Proceedings of the Institution of Mechanical Engineers, Part G:

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Multistage axial compressor is one of the key components in aero engines and gas turbines. In this paper, a five-stage axial compressor was studied to improve the efficiency. First, the loss analyses of the datum compressor were performed. The results showed that front rotors and rear stators have higher loss. Based on the loss analyses, the corresponding flow controls were introduced. The endwall treatment was performed with the rear stators, S3, S4, and S5, by end-bow, which changed the blade loading and reduced the loss due to endwall boundary layer. The efficiency of the datum compressor was increased by 0.5%. Based on the improved redesign of rear stators, shock control was introduced to front rotors, R1 and R2, characterized by sweep, which changed the shock structure and decreased the shock-induced loss and shock-tip leakage interaction. Coupled between endwall treatment and shock control, compared to the datum compressor, the efficiency, peak pressure ratio, and choked mass flow were increased by 1.1%, 1.1%, and 1.2%, respectively. At off-design speeds, the performances were also improved, which implies the flow controls for design speed remain effective in a range of off-design speeds. The reliability of the redesigned compressor was validated by stress and mode analyses.

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Three-dimensional flow field downstream of an embedded stator in a multistage axial flow compressor: Part 1: Steady and unsteady flow fields

Cited by 7 publications

References 15 publications

Converged statistics for time-resolved measurements in low-speed axial fans using high-frequency response probes

Converged statistics for time-resolved measurements in low-speed axial fans using high-frequency response probes

Non-deterministic kinetic energy within the rotor wakes and boundary layers of low-speed axial fans: frequency-based decomposition of unforced unsteadiness and turbulence

Investigation of endwall treatment and shock control in a five-stage axial compressor

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