# Olaf Marxen

### Biography

### Biography

Lecturer, University of Surrey, Mechanical Engineering Sciences, 2014-Research Associate, Imperial College London, Department of Mechanical Engineering, 2013-2014Postdoctoral Researcher, von Karman Institute for Fluid Dynamics, 2011-2013Engineering Research Associate / Postdoctoral Fellow, Stanford University, Center for Turbulence Research, 2006-2011Postdoctoral Fellow, KTH Stockholm, 2005-2006Research Assistant, Universität Stuttgart, Institut für Aerodynamik und Gasdynamik, 1999-2005

### Teaching

ENG 3165 Numerical Methods & CFD

### My publications

### Publications

flow in a rotor/rotor cavity. The numerical tool used employs a

spectral element discretisation in two dimensions and a Fourier

expansion in the remaining direction, which is periodic and corresponds

to the azimuthal coordinate in cylindrical coordinates.

The spectral element approximation uses a Galerkin method to

discretise the governing equations, but employs high-order polynomials

within each element to obtain spectral accuracy. A

second-order, semi-implicit, stiffly stable algorithm is used for

the time discretisation. Numerical results obtained for the rotor/

stator cavity compare favourably with experimental results

for Reynolds numbers up to Re1 = 106 in terms of velocities and

Reynolds stresses. The buoyancy-driven flow is simulated using

the Boussinesq approximation. Predictions are compared with

previous computational and experimental results. Analysis of

the present results shows close correspondence to natural convection

in a gravitational field and consistency with experimentally

observed flow structures in a water-filled rotating annulus.

Predicted mean heat transfer levels are higher than the available

measurements for an air-filled rotating annulus, but in agreement

with correlations for natural convection under gravity.

turbine internal air systems, and are particularly challenging to

model due to the inherently unsteadiness of these flows. While

the global features of such flows are well documented, detailed

analyses of the unsteady structure and turbulent quantities have

not been reported. In this work we use a high-order numerical

method to perform large-eddy simulation (LES) of buoyancyinduced

flow in a sealed rotating cavity with either adiabatic or

heated disks. New insight is given into long-standing questions

regarding the flow characteristics and nature of the boundary

layers. The analyses focus on showing time-averaged quantities,

including temperature and velocity fluctuations, as well as on

the effect of the centrifugal Rayleigh number on the flow structure.

Using velocity and temperature data collected over several

revolutions of the system, the shroud and disk boundary layers

are analysed in detail. The instantaneous flow structure contains

pairs of large, counter-rotating convection rolls, and it is shown

that unsteady laminar Ekman boundary layers near the disks are

driven by the interior flow structure. The shroud thermal boundary

layer scales as approximately Ra

turbine internal air systems, and are particularly challenging to

model due to the inherently unsteadiness of these flows. While

the global features of such flows are well documented, detailed

analyses of the unsteady structure and turbulent quantities have

not been reported. In this work we use a high-order numerical

method to perform large-eddy simulation (LES) of buoyancyinduced

flow in a sealed rotating cavity with either adiabatic or

heated disks. New insight is given into long-standing questions

regarding the flow characteristics and nature of the boundary

layers. The analyses focus on showing time-averaged quantities,

including temperature and velocity fluctuations, as well as on

the effect of the centrifugal Rayleigh number on the flow structure.

Using velocity and temperature data collected over several

revolutions of the system, the shroud and disk boundary layers

are analysed in detail. The instantaneous flow structure contains

pairs of large, counter-rotating convection rolls, and it is shown

that unsteady laminar Ekman boundary layers near the disks are

driven by the interior flow structure. The shroud thermal boundary

layer scales as approximately Ra?1/3

, in agreement with observations

for natural convection under gravity.