Rotating Coherent Flow Structures as a Source for Narrowband Tip Clearance Noise from Axial Fan

2016 ◽  
Author(s):  
Tao Zhu ◽  
Dominic Lallier-Daniels ◽  
Marlene Sanjose ◽  
Stephane Moreau ◽  
Thomas H. Carolus
Keyword(s):  
Tip Clearance ◽  
Flow Structures ◽  
Axial Fan ◽  
Coherent Flow Structures

Rotating coherent flow structures as a source for narrowband tip clearance noise from axial fans

2018 ◽  
Vol 417 ◽  
pp. 198-215 ◽  
Author(s):  
Tao Zhu ◽  
Dominic Lallier-Daniels ◽  
Marlène Sanjosé ◽  
Stéphane Moreau ◽  
Thomas Carolus
Keyword(s):  
Tip Clearance ◽  
Flow Structures ◽  
Axial Fans ◽  
Coherent Flow Structures

Statistical Procedure to Obtain Accurate Time-Resolved Measurements in Turbomachinery Environments Using Fast-Response Probes

2012 ◽  
Author(s):  
Jesús Manuel Fernández Oro ◽  
Katia María Argüelles Díaz ◽  
María Rodríguez Lastra ◽  
Mónica Galdo Vega
Keyword(s):  
Time Integration ◽  
Power Spectra ◽  
Axial Flow ◽  
Complete Information ◽  
Fast Response ◽  
Statistical Procedure ◽  
Tip Clearance ◽  
Flow Structures ◽  
Axial Fan ◽  
Time Resolved

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 inter-regions, 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 well-designed periodograms or power spectra with minimum scatter and large periods of time integration. This work presents the general guidelines that any statistical procedure must follow to assure that phase-locked averaging results are consistent when applied to velocity signals in multistage turbomachinery. The procedure is established in terms of convergence (residuals) and coherence (error) between time-resolved 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. The proposed methodology is applied to a low-speed axial fan, so a concise survey of usual practices employed by other authors in the literature is firstly reviewed, in order to identify fundamental parameters and values typically adopted to guarantee convergence. Finally, recommendations are made as a function of the variable analysed, the wake pattern to be described or the global disorder of the flow structures inside axial flow fans.

Characterization of Coherent Flow Structures in a Swirl-Stabilized Spray Combustor

2021 ◽  
Author(s):  
Nicholas Rock ◽  
Scott D. Stouffer ◽  
Tyler H. Hendershott ◽  
Edwin Corporan ◽  
Paul Wrzesinski
Keyword(s):  
Flow Structures ◽  
Coherent Flow Structures

scholarly journals Design-Assisted of Pitching Aerofoils through Enhanced Identification of Coherent Flow Structures

Designs ◽  
2021 ◽  
Vol 5 (1) ◽  
pp. 11 ◽  
Author(s):  
Filippo Avanzi ◽  
Francesco De Vanna ◽  
Yin Ruan ◽  
Ernesto Benini
Keyword(s):  
Pressure Field ◽  
Navier Stokes ◽  
Flow Structures ◽  
Coupled Modes ◽  
Spectral Reconstruction ◽  
Sst Turbulence Model ◽  
Coherent Flow Structures ◽  
Highly Correlated ◽  
Naca 0012 ◽  
Proper Orthogonal

This study discusses a general framework to identify the unsteady features of a flow past an oscillating aerofoil in deep dynamic stall conditions. In particular, the work aims at demonstrating the advantages for the design process of the Spectral Proper Orthogonal Decomposition in accurately producing reliable reduced models of CFD systems and comparing this technique with standard snapshot-based models. Reynolds-Averaged Navier-Stokes system of equations, coupled with k−ω SST turbulence model, is used to produce the dataset, the latter consisting of a two-dimensional NACA 0012 aerofoil in the pitching motion. Modal analysis is performed on both velocity and pressure fields showing that, for vectored values, a proper tuning of the filtering process allows for better results compared to snapshot formulations and extract highly correlated coherent flow structures otherwise undetected. Wider filters, in particular, produce enhanced coherence without affecting the typical frequency response of the coupled modes. Conversely, the pressure field decomposition is drastically affected by the windowing properties. In conclusion, the low-order spectral reconstruction of the pressure field allows for an excellent prediction of aerodynamic loads. Moreover, the analysis shows that snapshot-based models better perform on the CFD values during the pitching cycle, while spectral-based methods better fit the loads’ fluctuations.

Experiments on an Axial Fan Stage: Time-Resolved Analysis of Rotating Instability Modes

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Benjamin Pardowitz ◽  
Ulf Tapken ◽  
Lars Neuhaus ◽  
Lars Enghardt
Keyword(s):  
Leading Edge ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Axial Fan ◽  
Time Resolved ◽  
Instability Waves ◽  
Instability Modes ◽  
Mode Decomposition ◽  
Rotating Instability ◽  
Annular Cascade

Rotating instability (RI) occurs at off-design conditions in axial compressors, predominantly in rotor configurations with large tip clearances. Characteristic spectral signatures with side-by-side peaks below the blade passing frequency (BPF) are typically referred to RI located in the clearance region next to the leading edge (LE). Each peak can be assigned to a dominant circumferential mode. RI is the source of the clearance noise (CN) and an indicator for critical operating conditions. Earlier studies at an annular cascade pointed out that RI modes of different circumferential orders occur stochastically distributed in time and independently from each other, which is contradictory to existing explanations of RI. Purpose of the present study is to verify this generally with regard to axial rotor configurations. Experiments were conducted on a laboratory axial fan stage mainly using unsteady pressure measurements in a sensor ring near the rotor LE. A mode decomposition based on cross spectral matrices was used to analyze the spectral and modal RI patterns upstream of the rotor. Additionally, a time-resolved analysis based on a spatial discrete-Fourier-transform (DFT) was applied to clarify the temporal characteristics of the RI modes and their potential interrelations. The results and a comparison with the previous findings on the annular cascade corroborate a new hypothesis about the basic RI mechanism. This hypothesis implies that instability waves of different wavelengths are generated stochastically in a shear layer resulting from a backflow in the tip clearance region.

scholarly journals Entropy Analysis of the Flat Tip Leakage Flow with Delayed Detached Eddy Simulation

Entropy ◽  
2018 ◽  
Vol 21 (1) ◽  
pp. 21 ◽  
Author(s):  
Hui Li ◽  
Xinrong Su ◽  
Xin Yuan
Keyword(s):  
Tip Clearance ◽  
Flow Structures ◽  
Leakage Flow ◽  
Detached Eddy Simulation ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Passage Vortex ◽  
Unsteady Effects

In unshrouded turbine rotors, the tip leakage vortices develop and interact with the passage vortices. Such complex leakage flow causes the major loss in the turbine stage. Due to the complex turbulence characteristics of the tip leakage flow, the widely used Reynolds Averaged Navier–Stokes (RANS) approach may fail to accurately predict the multi-scale turbulent flow and the related loss. In order to effectively improve the turbine efficiency, more insights into the loss mechanism are required. In this work, a Delayed Detached Eddy Simulation (DDES) study is conducted to simulate the flow inside a high pressure turbine blade, with emphasis on the tip region. DDES results are in good agreement with the experiment, and the comparison with RANS results verifies the advantages of DDES in resolving detailed flow structures of leakage flow, and also in capturing the complex turbulence characteristics. The snapshot Proper Orthogonal Decomposition (POD) method is used to extract the dominant flow features. The flow structures and the distribution of turbulent kinetic energy reveal the development of leakage flow and its interaction with the secondary flow. Meanwhile, it is found that the separation bubble (SB) is formed in tip clearance. The strong interactions between tip leakage vortex (TLV) and the up passage vortex (UPV) are the main source of unsteady effects which significantly enhance the turbulence intensity. Based on the DDES results, loss analysis of tip leakage flow is conducted based on entropy generation rates. It is found that the viscous dissipation loss is much stronger than heat transfer loss. The largest local loss occurs in the tip clearance, and the interaction between the leakage vortex and up passage vortex promotes the loss generation. The tip leakage flow vortex weakens the strength of up passage vortex, and loss of up passage flow is reduced. Comparing steady and unsteady effects to flow field, we found that unsteady effects of tip leakage flow have a large influence on flow loss distribution which cannot be ignored. To sum up, the current DDES study about the tip leakage flow provides helpful information about the loss generation mechanism and may guide the design of low-loss blade tip.

scholarly journals Experimental study of coherent flow structures past a wall-mounted square cylinder

2019 ◽  
Vol 182 ◽  
pp. 137-146 ◽  
Author(s):  
Maria Ikhennicheu ◽  
Grégory Germain ◽  
Philippe Druault ◽  
Benoît Gaurier
Keyword(s):  
Experimental Study ◽  
Flow Structures ◽  
Square Cylinder ◽  
Coherent Flow Structures
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