Direct Numerical Simulation of Global Instability in a Hole-Tone Feedback System

2011 ◽  
Author(s):  
Kazuo Matsuura ◽  
Masami Nakano
Keyword(s):  
Pressure Fluctuation ◽  
Feedback System ◽  
Computational Results ◽  
Helical Structures ◽  
Tone Frequency ◽  
Vortical Structures ◽  
End Plate ◽  
Fluctuation Field ◽  
Air Jet ◽  
Pod Analysis

Direct computations and experiments of a hole-tone feedback system are conducted. The mean velocities of an air-jet are 8 and 10 m/s in the computations, 6–13 m/s in the experiments. The diameters of a nozzle and an end plate hole are both 50 mm, and an impingement length between the nozzle and the end plate is 50 mm. The computational results agree well with the experimental data in terms of qualitative vortical structures and a relationship between the most dominant hole-tone frequency and a jet speed. Based on the computational results of the air-jet speed of 8 m/s, a Proper Orthogonal Decomposition (POD) analysis of the whole pressure fluctuation field is conducted. The 1st and 2nd POD modes are nearly in anti-phase, and alternatively appearing helical structures are observed upstream of the end plate hole in an isosurface plot of the eigenfunctions of the modes. Dominant behaviors of vortex shedding from the end plate hole are represented by the 3rd and 4th modes. As the result, dominant variation of the pressure fluctuation field is successfully extracted by the present POD analysis.

A throttling mechanism sustaining a hole tone feedback system at very low Mach numbers

2012 ◽  
Vol 710 ◽  
pp. 569-605 ◽  
Author(s):  
K. Matsuura ◽  
M. Nakano
Keyword(s):  
Pressure Fluctuation ◽  
Feedback System ◽  
Peak Frequency ◽  
Computational Results ◽  
Mean Velocity ◽  
Vortical Structures ◽  
End Plate ◽  
Air Jet ◽  
The Mean ◽  
Fluctuation Fields

AbstractThis study investigates the sound produced when a jet, issued from a circular nozzle or hole in a plate, goes through a similar hole in a second plate. The sound, known as a hole tone, is encountered in many practical engineering situations. Direct computations of a hole tone feedback system were conducted. The mean velocity of the air jet was 10 m s−1. The nozzle and the end plate hole both had a diameter of 51 mm, and the impingement length between the nozzle and the end plate was 50 mm. The computational results agreed well with past experimental data in terms of qualitative vortical structures, the relationship between the most dominant hole tone peak frequency and the jet speed, and downstream growth of the mean jet profiles. Based on the computational results, the shear-layer impingement on the hole edge, the resulting propagation of pressure waves and the associated vortical structures are discussed. To extract dominant unsteady behaviours of the hole tone phenomena, a snapshot proper orthogonal decomposition (POD) analysis of pressure fluctuation fields was conducted. It was found that the pressure fluctuation fields and the time variation of mass flows through the end plate hole were dominantly expressed by the first and second POD modes, respectively. Integrating the computational results, an axisymmetric throttling mechanism linking mass flow rates through the hole, vortex impingement and global pressure propagation, is proposed.

Organized motions in a fully developed turbulent axisymmetric jet

1989 ◽  
Vol 203 ◽  
pp. 425-448 ◽  
Author(s):  
Jin Tso ◽  
Fazle Hussain
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Small Scale ◽  
Shear Strain Rate ◽  
Helical Structures ◽  
Vortical Structures ◽  
Axisymmetric Jet ◽  
Air Jet ◽  
Scale Turbulence ◽  
Structure Configuration

An experiment has been conducted to study the occurrence, configuration and dynamics of large-scale coherent vortical motions in the fully developed region of a turbulent axisymmetric jet. The key idea is to use vorticity signals from a spatial grid to detect and sample large-scale vortical structures and then use the (smoothed) vorticity peaks of spatial vorticity patterns to align and ensemble average successive realizations to determine structure configuration and dynamics. Measurements were made in an air jet at ReD = 69000 by employing a radial rake of seven × -wires to obtain the azimuthal vorticity map. Two additional conditioning probes were placed ± 90° away from the rake to determine the three-dimensional phase and hence the structure configuration. Structures with axisymmetric, helical and double helical configurations have been educed. Among them, the helical structures are far more dominant than the others, and the jet dynamics are thus discussed in terms of these helical structures. Helical structures move radially outward as they advect downstream. This radial movement, in conjunction with simultaneous local ejection of turbulent fluid and subsequent entrainment of the ejected fluid with ambient fluid, appears to be a major means of jet spreading. The shear strain rate is strong on the downstream side of the structure, causing intense small-scale turbulence production and mixing there.

Disorganization of a hole tone feedback loop by an axisymmetric obstacle on a downstream end plate

2014 ◽  
Vol 757 ◽  
pp. 908-942 ◽  
Author(s):  
K. Matsuura ◽  
M. Nakano
Keyword(s):  
Nozzle Exit ◽  
Passive Control ◽  
Control Method ◽  
Three Dimensional ◽  
Acoustic Power ◽  
Shear Layers ◽  
Mean Velocity ◽  
End Plate ◽  
Air Jet ◽  
Practical Engineering

AbstractThis study investigates the suppression of the sound produced when a jet, issued from a circular nozzle or hole in a plate, goes through a similar hole in a second plate. The sound, known as a hole tone, is encountered in many practical engineering situations. The mean velocity of the air jet $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}u_0$ was $6\text {--}12\ \mathrm{m}\ {\mathrm{s}}^{-1}$. The nozzle and the end plate hole both had a diameter of 51 mm, and the impingement length $L_{im}$ between the nozzle and the end plate was 50–90 mm. We propose a novel passive control method of suppressing the tone with an axisymmetric obstacle on the end plate. We find that the effect of the obstacle is well described by the combination ($W/L_{im}$, $h$) where $W$ is the distance from the edge of the end plate hole to the inner wall of the obstacle, and $h$ is the obstacle height. The tone is suppressed when backflows from the obstacle affect the jet shear layers near the nozzle exit. We do a direct sound computation for a typical case where the tone is successfully suppressed. Axisymmetric uniformity observed in the uncontrolled case is broken almost completely in the controlled case. The destruction is maintained by the process in which three-dimensional vortices in the jet shear layers convect downstream, interact with the obstacle and recursively disturb the jet flow from the nozzle exit. While regions near the edge of the end plate hole are responsible for producing the sound in the controlled case as well as in the uncontrolled case, acoustic power in the controlled case is much lower than in the uncontrolled case because of the disorganized state.

POD analysis on vortical structures in MVG wake by Liutex core line identification

2020 ◽  
Vol 32 (3) ◽  
pp. 497-509
Author(s):  
Xiang-rui Dong ◽  
Xiao-shu Cai ◽  
Yinlin Dong ◽  
Chaoqun Liu
Keyword(s):  
Vortical Structures ◽  
Line Identification ◽  
Core Line ◽  
Pod Analysis

Proper Orthogonal Decomposition and Extended- Proper Orthogonal Decomposition Analysis of Pressure Fluctuations and Vortex Structures Inside a Steam Turbine Control Valve

2018 ◽  
Vol 141 (4) ◽  
Author(s):  
Peng Wang ◽  
Hongyu Ma ◽  
Yingzheng Liu
Keyword(s):  
Proper Orthogonal Decomposition ◽  
Steam Turbine ◽  
Pressure Fluctuation ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Control Valve ◽  
Vortex Structures ◽  
Orthogonal Decomposition ◽  
Pod Analysis ◽  
Proper Orthogonal

In steam turbine control valves, pressure fluctuations coupled with vortex structures in highly unsteady three-dimensional flows are essential contributors to the aerodynamic forces on the valve components, and are major sources of flow-induced vibrations and acoustic emissions. Advanced turbulence models can capture the detailed flow information of the control valve; however, it is challenging to identify the primary flow structures, due to the massive flow database. In this study, state-of-the-art data-driven analyses, namely, proper orthogonal decomposition (POD) and extended-POD, were used to extract the energetic pressure fluctuations and dominant vortex structures of the control valve. To this end, the typical annular attachment flow inside a steam turbine control valve was investigated by carrying out a detached eddy simulation (DES). Thereafter, the energetic pressure fluctuation modes were determined by conducting POD analysis on the pressure field of the valve. The vortex structures contributing to the energetic pressure fluctuation modes were determined by conducting extended-POD analysis on the pressure–velocity coupling field. Finally, the dominant vortex structures were revealed conducting a direct POD analysis of the velocity field. The results revealed that the flow instabilities inside the control valve were mainly induced by oscillations of the annular wall-attached jet and the derivative flow separations and reattachments. Moreover, the POD analysis of the pressure field revealed that most of the pressure fluctuation intensity comprised the axial, antisymmetric, and asymmetric pressure modes. By conducting extended-POD analysis, the incorporation of the vortex structures with the energetic pressure modes was observed to coincide with the synchronous, alternating, and single-sided oscillation behaviors of the annular attachment flow. However, based on the POD analysis of the unsteady velocity fields, the vortex structures, buried in the dominant modes at St = 0.017, were found to result from the alternating oscillation behaviors of the annular attachment flow.

scholarly journals Pressure fluctuations beneath instability wavepackets and turbulent spots in a hypersonic boundary layer

2014 ◽  
Vol 756 ◽  
pp. 1058-1091 ◽  
Author(s):  
Katya M. Casper ◽  
Steven J. Beresh ◽  
Steven P. Schneider
Keyword(s):  
Boundary Layer ◽  
Pressure Fluctuation ◽  
Electrical Breakdown ◽  
Pressure Fluctuations ◽  
Spanwise Direction ◽  
Hypersonic Boundary Layer ◽  
Nozzle Wall ◽  
Turbulent Spots ◽  
Fluctuation Field ◽  
Second Mode

AbstractTo investigate the pressure-fluctuation field beneath turbulent spots in a hypersonic boundary layer, a study was conducted on the nozzle wall of the Boeing/AFOSR Mach-6 Quiet Tunnel. Controlled disturbances were created by pulsed-glow perturbations based on the electrical breakdown of air. Under quiet-flow conditions, the nozzle-wall boundary layer remains laminar and grows very thick over the long nozzle length. This allows the development of large disturbances that can be well-resolved with high-frequency pressure transducers. A disturbance first grows into a second-mode instability wavepacket that is concentrated near its own centreline. Weaker disturbances are seen spreading from the centre. The waves grow and become nonlinear before breaking down to turbulence. The breakdown begins in the core of the packets where the wave amplitudes are largest. Second-mode waves are still evident in front of and behind the breakdown point and can be seen propagating in the spanwise direction. The turbulent core grows downstream, resulting in a spot with a classical arrowhead shape. Behind the spot, a low-pressure calmed region develops. However, the spot is not merely a localized patch of turbulence; instability waves remain an integral part. Limited measurements of naturally occurring disturbances show many similar characteristics. From the controlled disturbance measurements, the convection velocity, spanwise spreading angle, and typical pressure-fluctuation field were obtained.

POD and Extended-POD Analysis of Pressure Fluctuations and Vortex Structures Inside a Steam Turbine Control Valve

2018 ◽  
Author(s):  
Peng Wang ◽  
Hongyu Ma ◽  
Yingzheng Liu
Keyword(s):  
Steam Turbine ◽  
Pressure Fluctuation ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Turbulence Models ◽  
Control Valve ◽  
Vortex Structures ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Pod Analysis

In steam turbine control valves, pressure fluctuations coupled with vortex structures in highly unsteady three-dimensional flows make essential contributions to aerodynamic forcing on the valve components, and are major sources of flow-induced vibration and acoustic effects. Advanced turbulence models, such as scale adaptive simulation (SAS), detached eddy simulation (DES) and large eddy simulation (LES), can capture detailed flow information of the control valve, but it is challenging to identify the primary flow structures due to the massive flow database. The present study used state-of-the-art data-driven analysis, namely proper orthogonal decomposition (POD) and extended-POD, to extract the energetic pressure fluctuations and dominant vortex structures of the control valve. To this end, the typical annular attachment flow inside a steam turbine control valve was investigated by performing a DES study. Subsequently, the energetic pressure fluctuation modes were extracted by performing POD analysis on the valve’s pressure field. The vortex structures contributing to these energetic pressure fluctuation modes were extracted by performing extended-POD analysis on the pressure-velocity coupling field. Finally, the dominant vortex structures were revealed directly by POD analysis of the valve’s velocity field. The results demonstrated that the flow instabilities inside the control valve were mainly induced by oscillations of the annular wall-attached jet and the derivative flow separations and reattachments. In POD analysis of the pressure field, the axial, antisymmetric and asymmetric pressure modes occupied most of the pressure fluctuation intensity. By further conducting extended-POD analysis, the vortex structures’ incorporation with the energetic pressure modes was identified as mainly attributed to the synchronous, alternating and single-sided oscillation behaviors of the annular attachment flow. However, based on POD analysis of the unsteady velocity fields, the vortex structures, buried in the dominant modes at St = 0.017, were found to result from alternating oscillations of the annular wall-attached jet.

The elliptic whistler jet

1999 ◽  
Vol 397 ◽  
pp. 23-44 ◽  
Author(s):  
HYDER S. HUSAIN ◽  
FAZLE HUSSAIN
Keyword(s):  
Flow Visualization ◽  
Near Field ◽  
Major Axis ◽  
Field Mass ◽  
Vortical Structures ◽  
Air Jet ◽  
Mass Entrainment ◽  
Circular Jets ◽  
Secondary Vortices ◽  
Axis Switching

Elliptic jets have decided advantages for technological applications over circular jets; this paper explores further advantages achieved by jet forcing due to self-excitation. Using hot-wire measurements and flow visualization, we have studied an elliptic whistler (i.e. self-excited) air jet of 2:1 aspect ratio which, in contrast to an elliptic jet issuing from a contoured nozzle, displays no axis switching, but significantly increased spread in the major-axis plane. Its near-field mass entrainment is considerably higher (by as much as 70%) than that of a non-whistling jet. Flow visualization reveals unexpected dynamics of the elliptic vortical structures in the whistler jet compared to that in the non-whistling jet. Vortices rolled up from the lip of the elliptic pipe impinge onto the collar, producing secondary vortices; interaction of these two opposite-signed vortices is shown to cause the different behaviour of the whistler jet.

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