The management of change in public organisations: A literature review

This article presents a review of the recent literature on change management in public organisations and sets out to explore the extent to which this literature has responded to earlier critiques regarding the lack of (public) contextual factors. The review includes 133 articles published on this topic in the period from 2000 to 2010. The articles are analyzed based on the themes of the context, content, process, outcome and leadership of change. We identified whether the articles referred to different orders of change, as well as their employed methods and theory. Our findings concentrate on the lack of detail on change processes and outcomes and the gap between the common theories used to study change. We propose an agenda for the study of change management in public organisations that focuses on its complex nature by building theoretical bridges and performing more in-depth empirical and comparative studies on c

Investigation of a Turbulent Wake in an Adverse Pressure Gradient using Laser Doppler Anemometry

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Spectral analysis of individual realization LDA data

The estimation of the autocorrelation function (act) or the spectral density function (sdt) from LDA data poses unique data-processing problems. The random sampling times in LDA preclude the use of the spectral methods for equi-spaced samples. As a consequence, special data-processing algorithms are used to process the LDA data. However, the random sampling causes an additional statistical variability of the spectral estimates that obscures the behaviour of the sdf in the high frequency range. The maximum frequency at which reliable estimates can be made is usually less than the mean data rate. For LDA measurements in gas flows the mean data rate is often small compared to the highest frequencies of the velocity fluctuations. As a consequence, the small scales of the turbulent fluctuations cannot be studied from the estimated sdf's with the presently available data-processing methods. It is the objective of the present study to modify an existing data-processing method such that information on the spectral density can be revealed at much higher frequencies. The modification consists of two elements. First, a locally sealed autocorrelation function is computed. This modification of the conventional slotting technique results in a much lower statistical variance at small lag times. Next, the locally scaled acf is cosine-transformed using a lag window whose width is varied with frequency. The modified estimator is applied to two types of stimulated data to illustrate its performance. It is shown that the modified slotting technique in conjunction with a variable window forms a powerful spectral estimator for low data density flows.Aerospace Engineerin

Drag Force on a Starting Plate Scales with the Square Root of Acceleration

We report results on the instantaneous drag force on plates that are accelerated in a direction normal to the plate surface, which show that this force scales with the square root of the acceleration. This is associated with the generation and advection of vorticity at the plate surface. A new scaling law is presented for the drag force on accelerating plates, based on the history force for unsteady flow. This scaling avoids previous inconsistencies in using added mass forces in the description of forces on accelerating plates. </p

Effect of surface roughness on heat transfer in Rayleigh-Bénard convection

This paper reports on an experimental study of the effects of surface roughness on the flow and heat transfer in cubical Rayleigh-Bénard convection cells for Rayleigh numbers between 107 and 1010. In the rough cells the top and bottom surfaces are equipped with square arrays of copper cubes. In line with other studies, three different regimes occur in the rough cells, with each regime having a different relation between the Nusselt number, Nu, and the Rayleigh number, Ra. In the first regime the Nu-Ra relation equals that of the smooth cell, but in the second and third regimes the Nu-Ra relation deviates from that of the smooth cell with significantly higher Nusselt numbers. To better understand these observations, the flow and temperature fields in both the smooth and rough cells were visualised by using particle image velocimetry with suspended thermochromic liquid crystals as flow tracer particles.Fluid MechanicsEKL-User

Investigation on the drag force and flow field of an accelerating plate

We present results on the instantaneous drag force acting on a rectangular plate that accelerates in a direction normal to the plate surface. Conventionally the drag force on an accelerating object is divided into a steady state term and an added mass term, which can both be time-dependent. However, for prolonged accelerations this theory does not hold. This paper shows a different method to scale the forces that act on an accelerating plate. We base this scaling on an experiment in which a plate was accelerated from rest through a water tank using an industrial gantry robot. In this experiment both the forces that act on the plate and the velocity fields, using PIV, were measured for a large range of accelerations and final velocities. The vorticity fields, obtained from the velocity fields, qualitatively show the same process of vortex formation across the whole range of accelerations. However, the instantaneous drag force and total circulation clearly differ for different accelerations. Shortly after the acceleration period ends, and the plate reaches its final velocity, the drag force and the circulation for different accelerations coincide and do not depend on the acceleration history anymore. We divided the force into two components: the steady state force, which can be scaled by using the drag coefficient, and an instationary force, for which we found a new scaling. This scaling, which involves the square root of both the velocity and the acceleration, can predict the instationary force significantly better than the conventional scaling.</p

Hydrodynamics of rowing propulsion

This paper presents the results of the time resolved flow field measurements around a realistic rowing oar blade that moves along a realistic path through water. To the authors' knowledge no prior account of this complex flow field has been given. Simultaneously with the flow field measurements, the hydrodynamic forces acting on the blade were measured. These combined measurements allow us to identify the relevant flow physics that governs rowing propulsion, and subsequently use this information to adjust the oar blade configuration to improve rowing propulsion. Analysis of the instationary flow field around the oar blade during the drive phase indicated how the initial formation, and subsequent development, of leading-edge and trailing-edge vortices are related to the generation of instationary lift and drag forces, and how these forces contribute to rowing propulsion. It is shown that the observed individual flow mechanisms are similar to the flow mechanisms observed in bird flight, but that the overall propulsive mechanism for rowing propulsion is fundamentally different. To quantify the rowing propulsion efficiency, we introduced the energetic efficiency and the impulse efficiency, where the latter can be interpreted as the alignment of the generated impulse with the propulsive direction. It is found that in the conventional oar blade configuration, the generated impulse is not aligned with the propulsive direction, indicating that the propulsion is suboptimal. By adjusting the angle at which the blade is attached to the oar, the generation of leading- A nd trailing-edge vortices is altered such that the generated impulse better aligns with the propulsive direction, thus increasing the efficiency.</p

Spectral analysis of individual realization LDA data

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Flamelesss combustion characteristics in a lab-scale furnace

Flameless combustion, named as Moderate or Intense Low-oxygen Dilution (MILD) combustion or high-temperature air combustion (HiTAC), is a promising technology to improve the thermal efficiency while suppressing NOx formation in combustion systems. Flameless combustion can occur when fresh air (and/or fuel) streams are sufficiently diluted by entrained combustion products before reactions take place. It has recently been experimentally studied on laboratory-scale setups because of scientific challenges, environmental concerns and its potential industrial applications. Some burning features in flameless combustion have been observed in jet-in-hot-coflow burners which use hot coflows generated by a secondary burner or diluting air with N2 or/and CO2 to mimic the diluted air which is actually diluted by burnt gases entrainment in furnaces. With the help of highspeed cameras, the time-resolved studies on such burners have been done experimentally. E. Oldenhof et al. [1] reported that the jet-in-hot-coflow flame is stabilized by autoignition kernels and the entrainment of hot oxidizer plays an important role in the formation of autoignition kernels[2]. As O2 level in coflow is reduced, reaction zone becomes less intense leading to a greater degree of partial premixing in these flames[3]. P. R. Medwell et al.[4] also concluded that large-scale vortices can lead to a weakening of the flame front or even local extinction leading to a form of partial premixing, and may contribute to the stabilization of the flameless combustion reaction zone. With low level (5% by volume) hydrogen addition in the fuel, the flame also exhibits autoignition kernels, but this was not observed at higher level (10% and 25%) hydrogen addition cases[5]. However, how can these findings be related to the flames in a furnace is still unclear because of the lack of similar experimental observations in furnace. </p

Analysis and Modelling of Physical Transport Phenomena

These lecture notes contain the course material Advanced Physical Transport Phenomena, offered in the Master’s programme in Applied Physics at Delft University of Technology. The notes follow in part the concept and content of the book Fysische Transportverschijnselen II (in Dutch) by Hoogendoorn and Van der Meer (Delft University Press, 1991). However, a significant amount of new material on turbulent flows, convective processes and numerical methods has now been included. The course aims at providing graduate students with an overview of analytical, numerical and modelling methods for solving problems of heat and fluid flow, following a unified and comparative approach