Daniel Michael Edgington-Mitchell

• PhD
• Professor (Associate) at Monash University (Australia)

This study identifies two previously unrecognised screech modes in non-axisymmetric jets. Spectral proper orthogonal decomposition (SPOD) of ultra-high-speed schlieren images reveals a bi-axial flapping mode in a rectangular jet and a quasi-helical mode in an elliptical jet. To educe the complex three-dimensional structure of these new modes, SPOD...

This work presents models for the behaviour of both upstream- and downstream-travelling waves in screeching elliptical jets. Proper orthogonal decomposition is performed on experimental velocity data in both the major and minor axis planes, for an aspect ratio $AR=2$ converging elliptical jet operating at nozzle pressure ratios of $2.6$ and $3.4$ ....

Guided-jet waves have been shown to close resonance loops in a myriad of problems such as screech and impingement tones in jets. These discrete, upstream-travelling waves have long been identified in linear-stability models of jet flows, but in this work they are instead considered in the context of an acoustic-scattering problem. It is shown that...

The rotating detonation engine is perhaps the most promising means to realize pressure-gain combustion in modern engines. The physical processes underpinning the dynamics of the combustion wave are complex, and a lack of understanding of these processes represents a significant barrier to practical implementation of the technology. A significant si...

This work focuses on the experimental characterisation of the acoustic field of an aspect-ratio-two elliptical jet, with comparison to the baseline axisymmetric jet. Measurements are taken at various azimuthal and polar observer angles across both the subsonic and supersonic regimes and are supplemented by particle-image-velocimetry measurements to...

Streaks in rectangular-jet flows are modeled using resolvent analysis, providing insight into the underlying physics of coherent structures. Two-dimensional, cross-plane resolvent analysis is used to evaluate the most-amplified coherent structures at very low frequencies. The highest-gain mode exhibits a large dipole-like structure, featuring a hig...

There is currently considerable interest in the guided-jet mode, as a result of recent works demonstrating it being the upstream component of various resonant systems in high-speed flows. For given jet operating conditions, the mode is known to exist over only a finite-frequency range that, for a twin-jet system, has been observed to vary with both...

Linear stability theory (LST) is often used to model the large-scale flow structures in the turbulent mixing region and near pressure field of high-speed jets. For perfectly expanded single round jets, these models predict the dominance of azimuthal wavenumbers $m=0$ and $m = 1$ helical modes for the lower frequency range, in agreement with empiric...

This work demonstrates a preliminary acoustic characterization of an installed elliptical jet with an aspect ratio of 2. This configuration is compared against the nominal axisymmetric installed jet case of equivalent diameter. A baseline case for the elliptical and axisymmetric nozzle geometries are obtained in the uninstalled configuration. For a...

Rectangular nozzle geometries offer a number of benefits over their axisymmetric counterparts, particularly for military aviation. Among these benefits are altered thermal and noise signatures, ease of airframe integration, and simpler thrust vectoring. Many next-generation tactical aircraft concepts employ two rectangular jets in close proximity....

The interaction of high-speed jets with a perpendicular surface produces not only broadband sound, but “impingement tones,” that can be more than 30 dB above the broadband noise. It is well recognized that these tones are the result of an aeroacoustic resonance, driven by a feedback loop between the jet nozzle and the plate. However, the exact mech...

As the global space industry expands, rockets are being launched from an increasing number of spaceports, including in Australia. As launch cadence increases to meet demand for space access and as vehicle optimization for weight and cost reduction becomes more pressing, noise has the potential to create harmful impacts—from vehicle vibroacoustic lo...

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...

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 eit...

The hydrodynamic characteristics and associated far-field acoustics of installed elliptical jets were studied using linear models based on the Navier–Stokes equations. A compressible elliptical vortex-sheet model predicted that the growth rates of the varicose [Formula: see text] and wagging [Formula: see text] modes decreased with the aspect ratio...

Shock-containing supersonic jets undergoing resonance processes are challenging from both a measurement and simulation perspective. These jets are host to a broad range of complex fluid phenomena: intense acoustic waves, turbulence, wavepackets and strong shock waves. Strong shocks present a challenge to both the experimental and numerical research...

Linear stability theory (LST) is often used to model the large-scale flow structures in the turbulent mixing region and near pressure field of high-speed jets. For perfectly-expanded single round jets, these models predict the dominance of $m=0$ and $m = 1$ helical modes for the lower frequency range, in agreement with empirical data. When LST is a...

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 energi...

An investigation of shock diffraction through a non-quiescent background medium is presented using both experimental and numerical techniques. Unlike diffracting shocks in quiescent media, a spatial distortion of the shock front occurs, producing a region of constant shock angle. An example of this process arises in the exhaust from a pulse-detonat...

We propose an approach to predict the modulation of wave packets in shock-containing jets. With a modeled ideally expanded mean flow as input, an approximation of the shock-cell structure is obtained from the parabolized stability equations (PSE) at zero frequency. This solution is then used to define a new shock-containing mean flow, which is a fu...

Linear stability theory (LST) is often used to model the large-scale flow structures in the turbulent mixing region and near pressure field of high-speed jets. For perfectly-expanded single round jets, these models predict the dominance of m = 1 helical modes for relatively small frequencies, in agreement with empirical data. Previous works have sh...

In this work we analyse the sound generation mechanism behind broadband shock-associated noise (BBSAN) using recently developed models that predict the characteristics of shock-cell modulation in the sound generating structures of the jet. The first model (spatially periodic linear stability analysis, SPLSA) is based on the assumption of periodicit...

The axisymmetric screech modes, which arise as part of a resonance cycle, are considered here for purely converging round twin-jets. Linear stability models, vortex-sheet and finite thickness, are employed to consider the underlying physics of the resonance involved. Strong agreement is found between both the models and experimental acoustic data,...

The authors have recently demonstrated that modal staging in screeching jets is governed by interaction between the Kelvin-Helmholtz wavepacket and one of several peaks in the axial wavenumber transform of the mean shock structure. In round jets, the axial decay of the spacing between shock cells manifests as a series of sub-optimal peaks in the me...

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 d...

Kiel probes have the potential to be a versatile tool for determining stagnation pressure gain in rotating detonation combustors (RDCs), accompanying the commonly used equivalent available pressure method. Although average pressure gain values determined with Kiel probes are comparable to those from thrust stand experiments, one can expect several...

Mitigation of pressure pulsations in the exhaust of a pulse detonation combustor is crucial for operation with a downstream turbine. For this purpose, a device termed the shock divider is designed and investigated. The intention of the divider is to split the leading shock wave into two weaker waves that propagate along separated ducts with differe...

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 an...

We propose a new approach to predict the modulation of wavepackets in shock-containing jets. With a modelled ideally expanded mean flow as input, an approximation of the shock-cell structure is obtained from the parabolised stability equations (PSE) at zero frequency. This solution is then used to define a new shock-containing mean flow, which is a...

View Video Presentation: https://doi.org/10.2514/6.2021-2249.vid A twin-jet vortex-sheet model is applied to study the axisymmetric screech modes, generated by simply converging nozzles, for low supersonic Mach numbers. This allows for the identification of the different waves supported by the flow for different conditions. Propagative regions for...

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 explanation for the existence of multiple axisymmetric modes at different freq...

We present a two-point model to investigate the underlying source mechanisms for broadband shock-associated noise (BBSAN) in shock-containing supersonic jets. In the model presented, the generation of BBSAN is assumed to arise from the nonlinear interaction between downstream-propagating coherent structures with the quasi-periodic shock cells in th...

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 an...

The present work focuses on the study of the resonance and coupling of an underexpanded circular twin-jet system operating at nozzle pressure ratio N P R = 5.0. Particle image velocimetry data from previous work was revisited, and a symmetry-imposed proper orthogonal decomposition (POD) was performed. It is shown that the system is dominated by a s...

An annular plenum is integrated downstream of six pulse detonation combustors arranged in a canannular configuration. The primary purpose of the plenum is the miti-gation of pressure and velocity fluctuations, which is crucial for operation with a downstream turbine. The flow inside the plenum is investigated by means of flush-mounted pressure tran...

In this paper we demonstrate that the use of multiple orifices can improve the fine particle fraction (FPF) of pressurised metered-dose inhaler solution formulations by up to 75% when compared to a single orifice with an equivalent cross sectional area (p<0.05). While prior work has relied on metal actuator components, improvements in micro injecti...

An annular plenum is integrated downstream of six pulse detonation combustors arranged in a can-annular configuration. The primary purpose of the plenum is the mitigation of pressure and velocity fluctuations, which is crucial for operation with a downstream turbine. The flow inside the plenum is investigated by means of flush-mounted pressure tran...

Kiel probes have the potential to be a versatile tool for determining stagnation pressure gain in rotating detonation combustors (RDCs). Although average pressure gain values determined with Kiel probes are comparable to those from thrust stand experiments, one can expect several interferences from the probe in unsteady trans-and supersonic flow. T...

In this study large-eddy simulations of under-expanded supersonic impinging jets are performed to develop a better understanding of the characteristics of the acoustic and hydrodynamic waves. Time history, dispersion relation and autocorrelation of the velocity and pressure fluctuations are used to investigate the propagation velocity, time and len...

We present a two-point model to investigate the underlying source mechanisms for broadband shock-associated noise (BBSAN) in shock-containing supersonic jets. In the model presented, the generation of BBSAN is assumed to arise from the non-linear interaction between downstream-propagating coherent structures with the quasi-periodic shock cells in t...

https://gfm.aps.org/meetings/dfd-2020/5f5b5574199e4c091e67bc46

This note investigates how small changes in the protrusion depth of a pressure transducer affect the pressure measurement of a moving shock wave. Measurements are undertaken with Kistler, Kulite and PCB sensors in flush, recessed and protruded sensor positions. Measurements of both absolute pressure and Mach number are shown to be insensitive to se...

Video link: https://gfm.aps.org/meetings/dfd-2020/5f5b5574199e4c091e67bc46 The pulse detonation engine (PDE) has the potential to drastically increase the efficiency of conventional gas turbines, which currently contain isobaric combustors. In a hybrid-PDE configuration, these combustors are replaced by an annular array of pulse detonation combust...

Acoustic measurements of unheated supersonic underexpanded jets with ideally expanded Mach numbers of 1.14, 1.38, and 1.50 are presented. Of the three components of supersonic jet noise, the focus is on the broadband shock-associated noise (BBSAN) component. Motivated by the modelling of BBSAN using the wavepacket framework, a traversable microphon...

An annular plenum is integrated downstream of six pulse detonation combustors arranged in a can-annular configuration. The primary purpose of the plenum is the mitigation of pressure and velocity fluctuations, which is crucial for operation with a downstream turbine. The flow inside the plenum is investigated by means of flush-mounted pressure tran...

The interaction between various wavelike structures in screeching jets is considered via both experimental measurements and linear stability theory. Velocity snapshots of screeching jets are used to produce a reduced order model of the screech cycle via proper orthogonal decomposition. Streamwise Fourier filtering is then applied to isolate the neg...

The dynamic evolution of a highly underexpanded transient supersonic jet at the exit of a pulse detonation engine is investigated via high-resolution time-resolved schlieren and numerical simulations. Experimental evidence is provided for the presence of a second triple shock configuration along with a shocklet between the reflected shock and the s...

The dynamic evolution of a highly underexpanded transient supersonic jet at the exit of a pulse detonation engine is investigated via high-resolution time-resolved schlieren and numerical simulations. Experimental evidence is provided for the presence of a second triple shock configuration along with a shocklet between the reflected shock and the s...

The exhaust flow of a pulse detonation combustor (PDC) is investigated for different operating conditions. The PDC consists of two units: the deflagration to detonation transition section, and the exhaust tube with a straight nozzle. High-speed high-resolution schlieren images visualize the shock dynamics downstream of the nozzle. The flow dynamics...

Mitigation of pressure pulsations in the exhaust of a pulse detonation combustor is crucial for operation with a downstream turbine. For this purpose, a device termed the shock divider is designed and investigated. The intention of the divider is to split the leading shock wave into two weaker waves that propagate along separated ducts with differe...

The exhaust of a pulse-detonation combustor is characterised by the emission of a high-amplitude primary shock wave and a trailing transient supersonic jet. Attenuation of this shock wave is of importance to the development of pulse-detonation combustors for use in gas turbines. One method of attenuation is to diffuse and redistribute the energy of...

The dynamic evolution of a highly underexpanded transient supersonic jet at the exit of a pulse detonation engine is investigated via high-resolution time-resolved schlieren and numerical simulations. Experimental evidence is provided for the presence of a second triple shock configuration along with a shocklet between the reflected shock and the s...

The exhaust flow of a Pulse Detonation Combustor (PDC) is investigated for different operating conditions. The PDC consists of two units, the deflagration to detonation transition section and the exhaust tube with a straight nozzle. High-speed high-resolution schlieren images visualize the shock dynamics downstream of the nozzle. The flow dynamics...

Understanding the factors that lead to breakup of liquid droplets is of interest in many applications. Liquid droplet breakup processes are typically broken into regimes based on a Weber number calculated based on an average flow velocity (Solsvik et al., 2013). In turbulent flows, the instantaneous velocity may differ significantly from the averag...

An experimental investigation into the influence of straight and converging nozzles on transient supersonic jet flow is presented. High-speed schlieren measurements are undertaken in detonation-driven pulse-detonation-combustor (PDC) flow and pressure- driven shock-tube flow. Flow from both the PDC and shock tube are shown to be qualitatively simil...

Non-intrusive temporally and spatially resolved measurements of dynamic phenomena are heavily reliant on high-speed (>1 kHz) digital scientific cameras. The cost of these cameras is a major constraint on the operation of many experimental and educational research facilities. In this paper we present a performance analysis of a low-cost high-speed C...

Time-resolved visualisation of shock wave motion within a powered resonant tube (PRT) is presented for the regurgitant mode of operation. Shock position and velocity are measured as functions of both time and space from ultra-high-speed schlieren visualisations. The shock wave velocity is seen to vary across the resonator length for both the incide...

Motivated by the success of wavepackets in modelling the noise from subsonic and perfectly expanded supersonic jets, we apply the wavepacket model to imperfectly expanded supersonic jets. Recent studies with subsonic jets have demonstrated the importance of capturing the ‘jitter’ of wavepackets in order to correctly predict the intensity of far-fie...

Supersonic jets, particularly shock-containing jets, often exhibit high-intensity, discrete-frequency acoustic tones. These tones are the signature of an aeroacoustic resonance loop established by the flow. This paper considers two of the classical forms of supersonic jet resonance: screech in shock-containing free jets and tones generated by the i...

The role of the external boundary conditions of the nozzle surface on the azimuthal mode selection of impinging supersonic jets is demonstrated for the first time. Jets emanating from thin- and infinite-lipped nozzles at a nozzle pressure ratio of $3.4$ and plate spacing of $5.0D$ , where $D$ is the nozzle exit diameter, are investigated using high...

The exhaust flow of a Pulse Detonation Combustor (PDC) is investigated for different operating conditions. The PDC consists of two units, the deflagration to detonation transition section and the exhaust tube with a straight nozzle. High-speed high-resolution schlieren images visualize the shock dynamics downstream of the nozzle. The flow dynamics...

Owing to their high thermodynamic efficiency, pulsating combustion cycles have become an attractive option for future gas turbine designs. Yet, their potential gains should not be outweighed by losses due to unsteady pressure wave interactions between engine components. Consequently, the geometric engine design moves into focus. Ideally, one would...

This paper investigates the broadband shock-associated noise (BBSAN) radiated from supersonic jets at the rootsource level. The sources are modeled according to an acoustic analogy. The acoustic-analogy model is informed byhigh-spatial-resolution two-dimensional two-component particle image velocimetry (PIV) data and solutions to theReynolds-averag...

Experimental evidence is provided to demonstrate that the upstream-travelling waves in two jets screeching in the A1 and A2 modes are not free-stream acoustic waves, but rather waves with support within the jet. Proper orthogonal decomposition is used to educe the coherent fluctuations associated with jet screech from a set of randomly sampled velo...

The acoustic analogy provides a general framework for predicting broadband jet noise. The accuracy of the noise predictions is strongly dependent on the second- and fourth-order integral time and length scales of the turbulence quantities in the jet. Two low-order models for the second- and fourth-order integral length scales are examined. The low-...

Proper orthogonal decomposition can be used to determine the dominant coherent structures present within a turbulent flow. In many flows, these structures are well represented by only a few high-energy modes. However, additional modes with clear spatial structure, but low-energy contribution can often be present in the proper orthogonal decompositi...

This article describes how seed funding from one major Australian University, designed to encourage interdisciplinary collaborations among academics, led to the implementation of a safe and sustainable energy supply at a community development project in remote Timor‐Leste. This article reflects on the process, the results, and insights developed du...