ORCID Profile
0000-0001-7831-8121
Current Organisation
Monash University
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Fluid mechanics and thermal engineering | Turbulent flows | Fluid-structure interaction and aeroacoustics | Fundamental and theoretical fluid dynamics
ANZSRC Socio-Economic Objective (SEO)
Related Links
Publications
Investigation of supersonic twin-jet coupling using spatial linear stability analysis
Publisher: Cambridge University Press (CUP)
Date: 14-05-2021
DOI: 10.1017/JFM.2021.366
Analysis of axisymmetric screech tones in round twin-jets using linear stability theory
Publisher: American Institute of Aeronautics and Astronautics
Date: 13-06-2022
DOI: 10.2514/6.2022-3071
Absolute instability in shock-containing jets
Publisher: Cambridge University Press (CUP)
Date: 08-11-2021
DOI: 10.1017/JFM.2021.887
Abstract: We present an analysis of the linear stability characteristics of shock-containing jets. The flow is linearised around a spatially periodic mean, which acts as a surrogate for a mean flow with a shock-cell structure, leading to a set of partial differential equations with periodic coefficients in space. Disturbances are written using the Floquet ansatz and Fourier modes in the streamwise direction, leading to an eigenvalue problem for the Floquet exponent. The characteristics of the solution are directly compared with the locally parallel case, and some of the features are similar. The inclusion of periodicity induces minor changes in the growth rate and phase velocity of the relevant modes for small shock litudes. On the other hand, the eigenfunctions are now subject to modulation related to the periodicity of the flow. Analysis of the spatio-temporal growth rates led to the identification of a saddle point between the Kelvin–Helmholtz mode and the guided jet mode, characterising an absolute instability mechanism. Frequencies and mode shapes related to the saddle points for two conditions (associated with axisymmetric and helical modes) are compared with screech frequencies and the most energetic coherent structures of screeching jets, resulting in a good agreement for both. The analysis shows that a periodic shock-cell structure has an impulse response that grows upstream, leading to oscillator behaviour. The results suggest that screech can occur in the absence of a nozzle, and that the upstream reflection condition is not essential for screech frequency selection. Connections to previous models are also discussed.
A model problem for sound radiation by an installed jet
Publisher: American Institute of Aeronautics and Astronautics
Date: 27-05-2016
DOI: 10.2514/6.2016-2857
A unifying theory of jet screech
Publisher: Cambridge University Press (CUP)
Date: 13-07-2022
DOI: 10.1017/JFM.2022.549
Abstract: This paper describes the mechanism underpinning modal staging behaviour in screeching jets. An upstream-propagating subsonic guided-jet mode is shown to be active in all stages of screech. Axial variation of shock-cell spacing manifests in the spectral domain as a series of suboptimal peaks. It is demonstrated that the guided-jet mode may be energized by interactions of the Kelvin–Helmholtz wavepacket with not only the primary shock wavenumber peak, but also suboptimal peaks interaction with suboptimals is shown to be responsible for closing the resonance loop in multiple stages of jet screech. A consideration of the full spectral representation of the shocks reconciles several of the classical models and results for jet screech that had heretofore been paradoxical. It is demonstrated that there are multiple standing waves present in the near field of screeching jets, corresponding to the superposition of the various waves active in these jets. Multimodal behaviour is explored for jets in a range of conditions, demonstrating that multiple peaks in the frequency spectra can be due to either changes in which peak of the shock spectra the Kelvin–Helmholtz wavepacket is interacting with, or a change in azimuthal mode, or both. The absence of modal staging in high-aspect-ratio non-axisymmetric jets is also explained in the context of the aforementioned mechanism. The paper closes with a new proposed theory for frequency selection in screeching jets, based on the observation that these triadic interactions appear to underpin selection of the guided-jet mode wavelength in all measured cases.
Acoustic radiation of a simplified jet-flap-thrust gate configuration: numerical and experimental investigation
Publisher: American Institute of Aeronautics and Astronautics
Date: 08-06-2020
DOI: 10.2514/6.2020-2604
Forcing statistics in resolvent analysis: application in minimal turbulent Couette flow
Publisher: Cambridge University Press (CUP)
Date: 10-12-2020
DOI: 10.1017/JFM.2020.918
The axisymmetric screech tones of round twin jets examined via linear stability theory
Publisher: Cambridge University Press (CUP)
Date: 15-06-2023
DOI: 10.1017/JFM.2023.398
Abstract: Spatial linear stability analysis is used to study the axisymmetric screech tones generated by twin converging round nozzles at low supersonic Mach numbers. Vortex-sheet and finite-thickness models allow for identification of the different waves supported by the flow at different conditions. Regions of the frequency–wavenumber domain for which the upstream-propagating guided jet modes are observed to be neutrally stable are observed to vary as a function of solution symmetry, jet separation, $S$ , and the velocity profile used. Screech-frequency predictions performed using wavenumbers obtained from both models agree well with experimental data. Predictions obtained from the finite-thickness model better align with the screech tones measured experimentally and so are seen to be an improvement on predictions made with the vortex sheet. Additionally, results from the finite-thickness model predict both symmetric and antisymmetric screech tones for low $S$ that are found in the vortex-sheet model only at greater $S$ . The present results indicate that the feedback loop generating these screech tones is similar to that observed for single-jet resonance, with equivalent upstream and downstream modes.
Dynamics of shear-layer coherent structures in a forced wall-bounded flow
Publisher: Cambridge University Press (CUP)
Date: 25-11-2020
DOI: 10.1017/JFM.2020.839
Steady and unsteady coupling in twin weakly underexpanded round jets
Publisher: Cambridge University Press (CUP)
Date: 23-05-2023
DOI: 10.1017/JFM.2023.275
Abstract: We investigate the intermittency of the coupling behaviour in screeching twin round supersonic jets at low Mach numbers across a range of nozzle spacings. Application of proper orthogonal decomposition combined with time-frequency wavelet analysis and spectral proper orthogonal decomposition shows that intermittency can manifest in twin jets as either a competition between the two symmetries, or the jets uncoupling and recoupling. The time scales on which symmetry switching occurs can vary strongly, ranging from $O(10^2)$ to $O(10^3)$ screech cycles. A transition from one symmetry to another is accompanied by a slight change in the screech frequency ranging from 0.30 % to 0.63 %. It was observed that complete uncoupling occurred only at the largest nozzle spacing of $s/D=6$ and at Mach numbers close to modal staging. When the jets are uncoupled they screech at slightly different frequencies, with a disparity of approximately 0.6 %. The coupling is particularly intermittent in the transition from the A1 to A2 branch, where the A2 mode is first observed, and tends toward steady coupling with increasing Mach number.
Acoustic radiation of subsonic jets in the vicinity of an inclined flat plate
Publisher: Acoustical Society of America (ASA)
Date: 07-2019
DOI: 10.1121/1.5115006
Abstract: Acoustic measurements of turbulent jets in the vicinity of a flat plate, mimicking a neighbouring wing, were compared to results from two wavepacket-based source models previously studied in the literature: the Tailored Green's Function method, which considers the radiation of the turbulent structure in the vicinity of a semi-infinite flat plate, and the Boundary Element Method, which can represent the full geometry of the plate used in the experiments. Particular interest is given to analysing how the angle of attack of the plate (α) affects the sound radiated by an installed jet with trailing edge 6 diameters away from the nozzle and 1 diameter away from the centerline for 0° ≤ α ≤ 45°. The results herein confirm the behaviour identified by the models: the scattered acoustic field follows the rotation of the plate, shifting a silence region with negligible scattered sound, and creating regions with lower noise levels in positions that correspond to the ground for an aircraft with engines under its wings. This is further explored by means of a Mach number analysis for M = 0.5, 0.7, and 0.9, showing that this trend is present whenever trailing-edge scattering of jet disturbances is dominant in the acoustic field.
Lift-up, Kelvin–Helmholtz and Orr mechanisms in turbulent jets
Publisher: Cambridge University Press (CUP)
Date: 26-05-2020
DOI: 10.1017/JFM.2020.301
Acoustic Radiation of Subsonic Jets at the Vicinity of an Inclined Flat Plate
Publisher: American Institute of Aeronautics and Astronautics
Date: 24-06-2018
DOI: 10.2514/6.2018-2976
Large-scale streaky structures in turbulent jets
Publisher: Cambridge University Press (CUP)
Date: 24-06-2019
DOI: 10.1017/JFM.2019.365
Abstract: Streaks have been found to be an important part of wall-turbulence dynamics. In this paper, we extend the analysis for unbounded shear flows, in particular a Mach 0.4 round jet, using measurements taken using dual-plane, time-resolved, stereoscopic particle image velocimetry (PIV) taken at pairs of jet cross-sections, allowing the evaluation of the cross-spectral density of streamwise velocity fluctuations resolved into azimuthal Fourier modes. From the streamwise velocity results, two analyses are performed: the evaluation of wavenumber spectra (assuming Taylor’s hypothesis for the streamwise coordinate) and a spectral proper orthogonal decomposition (SPOD) of the velocity field using PIV planes in several axial stations. The methods complement each other, leading to the conclusion that large-scale streaky structures are also present in turbulent jets where they experience large growth in the streamwise direction, energetic structures extending up to eight diameters from the nozzle exit. Leading SPOD modes highlight the large-scale, streaky shape of the structures, whose aspect ratio (streamwise over azimuthal length) is approximately 15. The data were further analysed using SPOD, resolvent and transient growth analyses, good agreement being observed between the models and the leading SPOD mode for the wavenumbers considered. The models also indicate that the lift-up mechanism is active in turbulent jets, with streamwise vortices leading to streaks. The results show that large-scale streaks are a relevant part of the jet dynamics.
Resolvent-based analysis of streaks in turbulent jets
Publisher: American Institute of Aeronautics and Astronautics
Date: 18-05-2019
DOI: 10.2514/6.2019-2569
Resolvent analysis applied to acoustic analogies
Publisher: American Institute of Aeronautics and Astronautics
Date: 18-05-2019
DOI: 10.2514/6.2019-2402
Prediction of Installed Jet Noise from Wave-Packet Models Tuned with Freejet Data
Publisher: American Institute of Aeronautics and Astronautics (AIAA)
Date: 04-2023
DOI: 10.2514/1.J062247
Abstract: In this work, a kinematic wave-packet model is used to predict installed-jet noise. Large-eddy simulation results of freejets, for Mach numbers 0.4 and 0.9, are used to obtain parameters of wave packets representing large-scale turbulent structures, which were used to provide a model source for the Lighthill analogy used to predict far-field noise spectra. The source litude in the model is calibrated using noise measurements for a freejet, and such a wave-packet source is used to predict noise of the same jet in an installed configuration using a tailored Green’s function. Results from the prediction model are compared to installed-jet experimental data for four different observer positions and a large range of frequencies. Overall, the model predicts both directivities and litudes similar to the experimental data, with a hump in the generated noise for lower Strouhal numbers and a clear peak near a Strouhal number of 0.2. This low-order model is fast and flexible, and it is expected to be helpful in preliminary aircraft design.
Study of Broadband Shock-Associated Noise using the Parabolised Floquet Equations
Publisher: American Institute of Aeronautics and Astronautics
Date: 13-06-2022
DOI: 10.2514/6.2022-3063
On the preference of round twin jets to present flapping oscillations
Publisher: American Institute of Aeronautics and Astronautics
Date: 13-06-2022
DOI: 10.2514/6.2022-3084
Understanding twin-jet screech using a vortex-sheet model
Publisher: American Institute of Aeronautics and Astronautics
Date: 28-07-2021
DOI: 10.2514/6.2021-2249
Closure mechanism of the A1 and A2 modes in jet screech
Publisher: Cambridge University Press (CUP)
Date: 07-02-2022
DOI: 10.1017/JFM.2022.58
Abstract: This paper explores the screech closure mechanism for different axisymmetric modes in shock-containing jets. While many of the discontinuities in tonal frequency exhibited by screeching jets can be associated with a change in the azimuthal mode, there has to date been no satisfactory explanation for the existence of multiple axisymmetric modes at different frequencies. This paper provides just such an explanation. As shown in previous works, specific wavenumbers arise from the interaction of waves in the flow with the shocks. This provides new paths for driving upstream-travelling waves that can potentially close the resonance loop. Predictions using locally parallel and spatially periodic linear stability analyses and the wavenumber spectrum of the shock-cell structure suggest that the A1 mode resonance is closed by a wave generated when the Kelvin–Helmholtz mode interacts with the leading wavenumber of the shock-cell structure. The A2 mode is closed by a wave that arises owing to the interaction between the Kelvin–Helmholtz wave and a secondary wavenumber peak, which arises from the spatial variation of the shock-cell wavelength. The predictions are shown to closely match experimental data, and possible justifications for the dominance of each mode are provided based on the growth rates of the absolute instability.
The colour of forcing statistics in resolvent analyses of turbulent channel flows
Publisher: Cambridge University Press (CUP)
Date: 25-11-2020
DOI: 10.1017/JFM.2020.802
A model problem for sound radiation by an installed jet
Publisher: Elsevier BV
Date: 03-2017
Screech mode staging in rectangular and elliptical jets
Publisher: American Institute of Aeronautics and Astronautics
Date: 13-06-2022
DOI: 10.2514/6.2022-3023
Numerical study of the hydrodynamic stability of a wind-turbine airfoil with a laminar separation bubble under free-stream turbulence
Publisher: AIP Publishing
Date: 08-2023
DOI: 10.1063/5.0159783
Abstract: The interaction of several instabilities and the influence of free-stream turbulence on laminar-turbulent transition on a 20% thick wind-turbine blade section with a laminar separation bubble (LSB) are investigated with wall-resolved large-eddy simulations (LES). Turbulence intensities (TI) of 0%, 2.2%, 4.5%, 8.6%, and 15.6% at chord Reynolds number 105 are considered. Linear receptivity occurs for the most energetic disturbances high-frequency perturbations are excited via non-linear mechanisms for TI≥8.6%. Unstable Tollmien–Schlichting (TS) waves appear in the inflectional flow region for TI≤4.5%, shifting to inviscid Kelvin–Helmholtz (KH) modes upon separation and forming spanwise rolls. Sub-harmonic secondary instability occurs for TI=0%, with rolls intertwining before transition. Streaks spanwise modulate the rolls and increase their growth rates with TI for TI≤4.5%, reducing separation and shifting transition upstream. The TI=4.5% case presents the highest perturbations, leading to the smallest LSB and most upstream transition. Earlier inception of TS/KH modes occurs on low-speed streaks, inducing premature transition. However, for TI=8.6%, the effect of the streaks is to stabilize the attached mean flow and front part of the LSB. This occurs due to the near-wall momentum deficit alleviation, leading to the transition delay and larger LSB than TI=4.5%. This also suppresses separation and completely stabilizes TS/KH modes for TI=15.6%. Linear stability theory predicts well the modal evolution for TI≤8.6%. Optimal perturbation analysis accurately computes the streak development upstream of the inflectional flow region but indicates higher lification than LES downstream due to the capture of low-frequency, oblique modal instabilities from the LSB. Only low- litude [O(1%)] streaks displayed exponential growth in the LES since non-linearity precludes the appearance of these modes.
Streaks and coherent structures in jets from round and serrated nozzles
Publisher: American Institute of Aeronautics and Astronautics
Date: 18-05-2019
DOI: 10.2514/6.2019-2597
Reduced-order Galerkin models of plane Couette flow
Publisher: American Physical Society (APS)
Date: 21-10-2022
Waves in screeching jets
Publisher: Cambridge University Press (CUP)
Date: 22-02-2021
HVAC noise simulations using direct and hybrid methods
Publisher: American Institute of Aeronautics and Astronautics
Date: 27-05-2016
DOI: 10.2514/6.2016-2855
Transition to chaos in a reduced-order model of a shear layer
Publisher: Cambridge University Press (CUP)
Date: 14-12-2021
Abstract: The present work studies the nonlinear dynamics of a shear layer, driven by a body force and confined between parallel walls, a simplified setting to study transitional and turbulent shear layers. It was introduced by Nogueira & Cavalieri ( J. Fluid Mech. , vol. 907, 2021, A32), and is here studied using a reduced-order model based on a Galerkin projection of the Navier–Stokes system. By considering a confined shear layer with free-slip boundary conditions on the walls, periodic boundary conditions in streamwise and spanwise directions may be used, simplifying the system and enabling the use of methods of dynamical systems theory. A basis of eight modes is used in the Galerkin projection, representing the mean flow, Kelvin–Helmholtz vortices, rolls, streaks and oblique waves, structures observed in the cited work, and also present in shear layers and jets. A dynamical system is obtained, and its transition to chaos is studied. Increasing Reynolds number $Re$ leads to pitchfork and Hopf bifurcations, and the latter leads to a limit cycle with litude modulation of vortices, as in the direct numerical simulations by Nogueira & Cavalieri. Further increase of $Re$ leads to the appearance of a chaotic saddle, followed by the emergence of quasi-periodic and chaotic attractors. The chaotic attractors suffer a merging crisis for higher $Re$ , leading to a chaotic dynamics with litude modulation and phase jumps of vortices. This is reminiscent of observations of coherent structures in turbulent jets, suggesting that the model represents a dynamics consistent with features of shear layers and jets.
Resolvent analysis in unbounded flows: role of free-stream modes
Publisher: Springer Science and Business Media LLC
Date: 27-02-2020
Wave-packet modulation in shock-containing jets
Publisher: American Physical Society (APS)
Date: 26-07-2022
Experimental study of turbulent-jet wave packets and their acoustic efficiency
Publisher: American Physical Society (APS)
Date: 12-2017
Related Organisations
Related Funding Activities
Discovery Early Career Researcher Award - Grant ID: DE240100933
Start Date: 2024
End Date: 12-2026
Amount: $458,183.00
Funder: Australian Research Council
View Funded Activity