# Oliver BuxtonImperial College London | Imperial · Department of Aeronautics

Oliver Buxton

Ph.D.

## About

28

Publications

3,220

Reads

**How we measure 'reads'**

A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more

508

Citations

Introduction

## Publications

Publications (28)

To investigate the influence of the orifice geometry on near-field coherent structures in a jet, Fourier-POD is applied. Velocity and vorticity snapshots obtained from tomographic particle image velocimetry at the downstream distance of two equivalent orifice diameters are analysed. Jets issuing from a circular orifice and from a fractal orifice ar...

Tomographic particle image velocimetry experiments were conducted in the near and intermediate fields of two different types of jet, one fitted with a circular orifice and another fitted with a repeating-fractal-pattern orifice. Breda & Buxton ( J. Vis. , vol. 21 (4), 2018, pp. 525–532; Phys. Fluids , vol. 30, 2018, 035109) showed that this fractal...

We investigate the properties of the velocity gradient tensor for spatially evolving turbulent flows (a near-wake, two axisymmetric jets and a planar mixing layer). Emphasis is placed on the study of the normal and non-normal parts of the tensor. Non-normality plays a greater role in the dynamics than is observed for HIT and does so for all spatial...

Multi-scale generated turbulent flows are observed to possess some remarkable features,
such as the rapid spreading of forest fires. Here, for simplicity, we consider the flow past a two-dimensional multi-scale arrangement of bars of various thicknesses in which wakes of different characteristic sizes and frequencies interact. We apply a novel mult...

There has been much debate over the past decade or so over the scaling of the thickness of the turbulent/nonturbulent (TNT) interface for turbulent shear flows. It is generally considered to consist of the outer viscous superlayer, in which viscous processes are significant, and an inner turbulent sublayer which is dominated by inertial processes....

Single-point hot-wire measurements are made downstream of a series of spanwise repeating obstacles that are used to generate an artificially thick turbulent boundary layer. The measurements are made in the near field, in which the turbulent boundary layer is beginning to develop from the wall-bounded wakes of the obstacles. The recent paper of Rodr...

We perform both high- and low-speed particle image velocimetry and torque measurements to characterize eight radial impeller types in an unbaffled stirred tank. The blade types consist of a set of regular flat blades, used as a baseline, regular blades of increased thickness, perforated blades, and fractal blades. We find a qualitative correlation...

This experimental study presents the effect of multiscale cut-in trailing edge serrations on the coherent structures shed into the wake of a lifting wing. Two-probe span-wise hot-wire traverses are performed to study spectra, coherence, and phase shift. In addition, planar particle image velocimetry is used to study the spatio-temporal structure of...

The wake behind a NACA0012 wing at incidence with cut-in sinusoidal trailing edges is experimentally investigated. A wing model with interchangeable trailing edges is used to study their impact on the wake properties. Both vertical and spanwise traverses of hot wires are done at different downstream positions to obtain the downstream evolution of s...

Previous wind-tunnel measurements have shown that fractal-shaped plates have increased drag compared to square plates of the same area. In this study, the power consumption and drag of turbines with fractal and rectangular blades in a stirred tank are measured. Power number decreases from rectangular to fractal impellers by over 10%, increasingly s...

A new technique of planar laser-induced fluorescence calibration is presented in this work. It accounts for a nonlinear dye response at high concentrations, an illumination light attenuation and a secondary fluorescence’s influence in particular. An analytical approximation of a generic solution of the Beer–Lambert law is provided and utilized for...

This paper examines the evolution of perturbations generated by various trips in a zero pressure gradient turbulent boundary layer. Measurements taken using hot-wire anemometry show that the evolution of the boundary layer towards the natural state is strongly dependent on the trip geometry. In particular the mechanisms creating the boundary layer...

The interaction between large- and small-scale fluctuations in turbulent flow is not only of great fundamental interest but an understanding of these interactions is fundamental to the modelling of the sub-grid scale (SGS) stresses in a large eddy simulation (LES). Particle image velocimetry (PIV) data is acquired with two different spatial resolut...

The modulation of small-scale velocity and velocity gradient quantities by concurrent large-scale velocity fluctuations is observed by consideration of the Kullback–Leibler divergence. This is a measure that quantifies the loss of information in modelling a statistical distribution of small-scale quantities conditioned on concurrent positive large-...

A new method for the triple decomposition of a multiscale flow, which is based on the novel optimal mode decomposition (OMD) technique, is presented. OMD provides low order linear dynamics, which fits a given data set in an optimal way and is used to distinguish between a coherent (periodic) part of a flow and a stochastic fluctuation. The method n...

The present paper describes a method to extrapolate the mean wall shear stress, \(\tau _{wall}\) , and the accurate relative position of a velocity probe with respect to the wall, \(\Delta y\) , from an experimentally measured mean velocity profile in a turbulent boundary layer. Validation is made between experimental and direct numerical simulatio...

This paper examines the kinematic behaviour the reduced velocity gradient tensor (VGT), (A) over bar (y), which is defined as a 2 x 2 block, from a single interrogation plane, of the full VGT A(ij) = partial derivative u(1)/partial derivative x(j). Direct numerical simulation data from the fully developed turbulent region of a nominally two-dimensi...

The interaction between the large- and small-scales in the self-similar region of a nominally two-dimensional planar mixing layer is examined at a centreline Reynolds number Reλ ≈ 260 (where Reλ is the Reynolds number based on Taylor microscale). Particle image velocimetry experiments are performed at two different spatial resolutions, one that cap...

The convection velocity of large and intermediate scale velocity fluctuations in a nominally two-dimensional planar mixing layer, and its dependence upon the length scale, is explored by carrying out particle image velocimetry (PIV) experiments. A "global" convection velocity, containing the convection of all the length scales present in the flow,...

The effect of numerical differentiation is investigated in the context of evaluating fluctuating velocity and scalar quantities in turbulent flows. In particular, 2-point forward-difference and 3-, 5-, 7-, and 9-point centred-difference schemes are investigated. The spectral technique introduced by Wyngaard (in J Sci Instr 1(2):1105–1108, 1968) for...

Particle image velocimetry (PIV) experiments that resolve a range of scales from 1.5L to 10.4η, where L and η are the integral and Kolmogorov length scales respectively, are performed in the self similar region of a nominally two dimensional planar mixing layer. Data is acquired at 7.25Hz with a field of view that extends to 1.5L thereby permitting...

The effect of spatial resolution and experimental noise on the kinematic fine-scale features in shear flow turbulence is investigated
by means of comparing numerical and experimental data. A direct numerical simulation (DNS) of a nominally two-dimensional
planar mixing layer is mean filtered onto a uniform Cartesian grid at four different, progress...

Direct numerical simulation data from the self similar region of a planar mixing layer is filtered at four different length scales, from the Taylor microscale to the dissipative scales, and is used to examine the scale dependence of the strain-rotation interaction in shear flow turbulence. The interaction is examined by exploring the alignment betw...

The three-dimensional structure and behaviour of the rate of rotation and strain rate tensors is examined in the far field of a turbulent planar two dimensional mixing layer. The mixing layer is simulated using the incompact3d DNS code at Reynolds number based on inlet conditions of 1000. The study looks at the effect of spatial resolution on the l...

The amplification of enstrophy is explored using cinematographic stereoscopic particle image velocimetry data. The enstrophy production rate is investigated by observation of the statistical tendency of the vorticity vector (ω) to align with the eigenvectors of the rate of strain tensor (ei). Previous studies have shown that ω preferentially aligns...

The structure of a fully turbulent axisymmetric jet, at Reynolds number based on jet exit conditions of 5000, is investigated with cinematographic (1 kHz) stereoscopic PIV in a plane normal to the jet axis. Taylor's hypothesis is employed to calculate all three velocity gradients in the axial direction. The technique's resolution allows all terms o...