A study of the interaction of one-sided flow over a compliant surface is presented. When fluid passes over a flexible surface the simultaneous interaction between the flow and structure gives rise to vibrations and instabilities on the surface as well as in the fluid. The fluid-structure interaction (FSI) has potential to be used in the control of boundary layer dynamics to achieve drag reduction through transition delay. The modelling and control of FSI systems apply to many fields of engineering beyond drag reduction, for example: the modelling and analysis of biomechanical systems; natural environmental systems; aero-elastics; and other areas where flow interacts moving or compliant boundaries. The investigation is performed through numerical simulation. This returns more detail than could be resolved through experiments, while also permitting the study of finite compliant surfaces that are prohibitively difficult, or impossible, to study with analytical techniques. In the present work, novel numerical modelling methods are developed from linear system analysis through to nonlinear disturbances and viscous effects. / Two numerical modelling techniques are adopted to approach the analysis of the FSI system. A potential-flow method is used for the modelling of flows in the limit of infinite Reynolds numbers, while a grid-free Discrete Vortex Method (DVM) is used for the modelling of the rotational boundary-layer flow at moderate Reynolds numbers. In both inviscid and viscous studies, significant contributions are made to the numerical modelling techniques. The application of these methods to the study of flow over compliant panels gives new insight to the nature of the FSI system. In the linear inviscid model, a novel hybrid computational/theoretical method is developed that evaluates the eigenvalues and eigenmodes from a discretised FSI system. The results from the non-linear inviscid model revealed that the steady-state of the non-linear wall motion is independent of initial excitation. For the viscous case, the first application of a DVM to model the interaction of a viscous, rotational flow with a compliant surface is developed. This DVM is successfully applied to model boundary-layer flow over a finite compliant surface.

A plane jet is a statistically two-dimensional flow, with the dominant flow in the streamwise (x) direction, spread in the lateral (y) direction and zero entrainment in the spanwise (z) direction respectively (see Figure 1). A plane jet has several industrial applications, mostly in engineering environments, although seldom is a jet issuing through a smooth contoured nozzle encountered in real life. Notably, the Reynolds number and boundary conditions between industrial and laboratory environments are different. In view of these, it is important to establish effects of nozzle boundary conditions as well as the influence of Reynolds number, on jet development. Such establishments are essential to gain an insight into their mixing field, particularly relevant to engineering applications. To satisfy this need, this thesis examines the influence of boundary conditions, especially those associated with the formation of the jet and jet exit Reynolds number, on the flow field of a turbulent plane air jet by measuring velocity with a hot wire anemometer. A systematic variation is performed, of the Reynolds number Re over the range 1,500≤Re ≤16,500, the inner-wall nozzle contraction profile r* over the range 0≤r*≤3.60 and nozzle aspect ratio AR over the range 15≤AR≤72 (see notation for symbols). An independent assessment of the effect of sidewalls on a plane jet is also performed. Key outcomes are as follows: (1) Effects of Reynolds number Re: Both the mean and turbulence fields show significant dependence on Re. The normalized initial mean velocity and turbulence intensity profiles are Re-dependent. An increase in the thickness of boundary layer at the nozzle lip with a decrease in Re is evident. This dependence appears to become negligible for Re ≥10,000. The centerline mean velocity decay and jet spreading rates are found to decrease as Re is increased. Furthermore, the mean velocity field appears to remain sensitive to Reynolds number at Re = 16,500. Unlike the mean velocity field, the turbulent velocity field has a negligible Re-dependence for Re ≥10,000. An increase in Reynolds number leads to an increase in the entrainment rate in the near field but a reduced rate in the far field. The centerline skewness and the flatness factors show a systematic dependence on Reynolds number too. (2) Effects of the inner-wall nozzle exit contraction profile r*: The inner-wall nozzle exit contraction profile r* influences the initial velocity and turbulence intensity profiles. Saddle-backed mean velocity profiles are evident for the sharp-edged orifice configuration (r* ≈ 0) and top hat profiles emerge when r* ≥1.80. As r* is increased from 0 to 3.60, both the near and the far field decay and the spreading rates of the plane jet are found to decrease. Hence, the sharp-edged orifice-jet (r* ≈ 0) decays and spreads more rapidly than the jet through a radially contoured configuration (r* ≈ 3.60). The asymptotic values of the center-line turbulence intensity, skewness and flatness factors of the velocity fluctuations increase as r* tends toward zero. The non-dimensional vortex shedding frequency of StH ≈ 0.39, is higher for the sharp-edged orifice nozzle (r*≈ 0), than for the radially contoured (r* ≈ 3.60) nozzle whose StH ≈ 0.24. Thus, the vortex shedding should be strongly dependent on flow geometry and on nozzle boundary conditions. (3) Effects of nozzle aspect ratio AR: The initial velocity and turbulence intensity profiles are slightly dependent on nozzle aspect ratio of the plane air jet. It is believed that a coupled influence of the nozzle aspect ratio and sidewalls produce changes in the initial flow field. The axial extent over which a statistically 'two-dimensional' flow is achieved, is found to depend upon nozzle aspect ratio. This could be possibly due to the influence of the evolving boundary layer on the sidewalls or due to increased three-dimensionality, whose influence becomes significantly larger as nozzle aspect ratio is reduced. A statistically two dimensional flow is only achieved over a very limited extent for AR = 15. In the self-similar region, the rates of centreline velocity decay, spreading of the mean velocity field and jet entrainment increase with an increase in nozzle aspect ratio. An estimate of the critical jet aspect ratio, where three-dimensional effects first emerge and its axial location is made. Results show that the critical aspect ratio increases with nozzle aspect ratio up to AR <30. For AR≥30, the critical aspect ratio based on jet half width, attains a constant value of about 0.15. Thus, it appears that when the width of the flow approximately equals the spacing between the sidewalls, the plane air jet undergoes a transition from 2-D to 3-D. A distinct hump of the locally normalized turbulence intensity at an axial distance between 10 to 12 nozzle widths downstream, characterizes the centerline turbulence intensity for all nozzle aspect ratios. This hump is smaller when nozzle aspect ratio is larger. (4) Effects of the sidewalls: A jet issuing from a nozzle of AR = 60 and measured at Re = 7,000 is tested with sidewalls, i.e. plane-jet and without sidewalls, i.e. free-rectangular-jet. It is found that the entire flow field behaves differently for the two cases. The initial velocity profiles are top hat for both jets. The free rectangular jet decays and spreads more rapidly in both the near and far field. It is found that the free rectangular jet behaves statistically two-dimensional up to a shorter axial distance (x/H = 70) as opposed to the plane jet whose two-dimensional region extends up to x/H = 160. Also noted are that the axial extent of the two-dimensional region depends strongly on nozzle aspect ratio. Beyond the 2-D region, the free rectangular jet tends to behave, statistically, like a round jet. The locally normalized centerline turbulence intensity also depend on sidewalls. Turbulence intensity for the plane jet asymptotes closer to the nozzle (around x/H = 30) whereas for the free rectangular jet, turbulence intensity varies as far downstream as x/H = 100, and then asymptotes. A constant StH of 0.36 is found for the free rectangular jet whereas an StH of 0.22 is obtained for the plane jet. It is noted that the effects of jet exit Reynolds number, inner-wall nozzle exit contraction profile, nozzle aspect ratio and sidewalls on the plane air jet are all non-negligible. The effect of viscosity is expected to weaken with increased Reynolds number and this may contribute to the downstream effects on the velocity field. Both the nozzle contraction profile and nozzle aspect ratio provide different exit boundaries for the jet. Such boundary conditions not only govern the formation of the initial jet but also its downstream flow properties. Hence, the initial growth of the shear layers and the structures within these layers are likely to evolve differently with different boundary conditions. Thus, the interaction of the large-scale structures with the surroundings seems to depend on nozzle boundary conditions and consequently, influences the downstream flow. In summary, the present study supports the notion that the near and far fields of the plane jet are strongly dependent on Reynolds number and boundary conditions. Therefore, the present thesis contains immensely useful information that will be helpful for laboratory-based engineers in selection of appropriate nozzle configurations for industrial applications. / Thesis (Ph.D.)--School of Mechanical Engineering, 2005.

This thesis describes the refinements, modifications and additions to a prototype Very High Frequency (VHF) Boundary Layer (BL) Spaced Antenna (SA) radar initially installed at the University of Adelaide's Buckland Park field site in 1997. Previous radar observations of the lowest few kilometres of the atmosphere, in particular the Atmospheric Boundary Layer, have used Ultra-High Frequency (UHF) radars. Unlike VHF radars, UHF radars are extremely sensitive to hydro-meteors and have difficulty in distinguishing clear-air echoes from precipitation returns. The advantages and requirements of using a VHF radar to observe the lowest heights is discussed in conjunction with some of the limitations. The successful operation of the system over long periods has enabled in-depth investigation of the performance of the system in a variety of conditions and locations. Observations were made from as low as 300m and as high as 8 km, dependent upon conditions. Comparisons between the radar and alternative wind measuring devices were carried out and examined. The antenna system of the radar is a critical component which was analysed in depth and subsequently re-designed. Through the use of numerical models and mea- surements, evaluation of different designs was accomplished. Further calibration of the remaining components of the full system has enabled estimations of the absolute received power. Additional parameters which can be derived with a calibrated radar were compared with values obtained by other authors, giving favourable results. Full Correlation Analysis (FCA) is the predominant technique used in this work. A brief discussion of the background theory and parameters which can be measured is described. A simple one-dimensional model was developed and combined with a 'radar backscatter model' to investigate potential sources of errors in the parameters determined using FCA with the VHF Boundary Layer Radar. In particular, underes- timations in the wind velocity were examined. The integration of a Radio Acoustic Sounding System (RASS) to obtain tempera- ture profiles is discussed. The theory of RASS measurements including the limitations and considerations which are required for the VHF BL radar are given. The difficulties encountered trying to implement such a system and the subsequent success using a Stratospheric Tropospheric (ST) Profiler in place of the BL radar is presented. Taken as a whole this thesis shows the success of the VHF BL to obtain mea- surements from as low as 300m. The validation of this prototype radar provides an alternative and, in certain situations, a superior device with which to study the lower troposphere. / Thesis (Ph.D.)--Department of Physics and Mathematical Physics, 2001.

Experiments to generate multiple shock waves in an axisymmetric model at hypersonic speeds were conducted in a small reflected shock tunnel. Conical surfaces were used to generate shock waves inside a circular duct chosen to be representative of a scramjet combustor. These shock waves impinged on turbulent boundary layers to produce shock wave/boundary layer interactions (SWBLIs). In the process of observing this phenomenon, the commonly used empirical correlations of Korkegi were tested for accuracy, i.e. the combined pressure ratio across these shocks can be measured and compared to that predicted by these correlations. Korkegi correlates only with Mach number, and is independent of Reynolds number and on how the pressure is applied. A major contribution of this work is to examine how the details of the compression process effect separation. In this study, the history of applying the compression was varied. An analytical method was developed for theoretically estimating the onset of incipient separation using an integrated computation of the momentum flux contained in the boundary layer. By including the summed (negative) contribution of wall shear stress on the integrated momentum flux, the upstream history of the boundary layer was considered. The overall result has a form similar to the Korkegi correlations, plus an additional correction term relating to momentum loss through wall shear stress. The correction term was determined to be a second order effect, which explains why the Reynolds number independent Korkegi correlations work so well over such a large range of conditions. A hypersonic flow test condition conducive to the generation of high Reynolds number flows and turbulent boundary layer production was developed in a small reflected shock tunnel. The experimentally measured flow parameters were matched by numerical simulation using a number of in-house codes at The University of Queensland. This has allowed the unmeasured parameters which are numerically derived to be stated with greater confidence. An internal centre-body with a conical forebody was used to generate conditions of incipient separation. This provided benchmark data for comparison with subsequent experiments with multiple compressions. A semi-vertex angle of 15o was selected based on Large Eddy Simulation (LES) numerical results once the experimental and numerical static wall pressure and heat flux were matched. A two-cone experimental model, which provided for adjustment of the axial separation between the two shock systems, was tested at the same flow conditions as used in the single-cone experiments. A technique of incrementally moving the instrumentation (relative to the centre-body) and repeating the same condition to achieve high resolution in pressure and heat flux distributions with a limited number of transducers was successful. The results verified that it was possible to subject a hypersonic turbulent boundary layer to two quantified compression-expansion systems with an adjustable axial separation between them and capture the first reflected shock in a “shock trap” to remove it's influence from the second SWBLI. The data from this initial two-cone model provided non-separated pressure and heat flux data which was used as a reference to help interpret data from separated flows. The commercially available Reynolds Averaged Navier-Stokes (RANS) numerical code, CFD-Fastran, was used to help design an experimental model which produces boundary layer separation. Algebraic and two-equation turbulence models were applied to a modified two-cone model to show greater pressure rises which would produce boundary layer separation. A modified two-cone model was tested and demonstrated boundary layer separation. Three configurations with varying axial separation between SWBLIs were tested which all produced separation. The configuration that produced the largest pressure ratio and largest separation region at the second SWBLI may represent a geometry whereby the distance from the hollow cylinder inlet and the second cone may represent a critical value. The amount of viscous interaction, generated from the leading edge of the shock trap, and the proximity of the two interactions may be coupled to produce higher than expected values. It is postulated that the boundary layer momentum recovery for the configuration where the second SWBLI was furthest downstream (30 mm configuration), prevented severe separation from occurring. An in-house RANS code, elmer3, was used to simulate the flow of the modified two-cone model. An algebraic turbulence model was applied to this model and comparisons of experimentally measured static wall pressure and heat flux have given good agreement. The wall shear stress was investigated to provide further information concerning the position and size of flow reversal regions. The use of the numerical codes utilised in this study has reinforced their effectiveness for model design and comparison of experimental results.

<p>Two types of mesoscale wind-speed jet and their effects on boundary-layer structure were studied. The first is a coastal jet off the northern California coast, and the second is a katabatic jet over Vatnajökull, Iceland. Coastal regions are highly populated, and studies of coastal meteorology are of general interest for environmental protection, fishing industry, and for air and sea transportation. Not so many people live in direct contact with glaciers but properties of katabatic flows are important for understanding glacier response to climatic changes. Hence, the two jets can potentially influence a vast number of people.</p><p>Flow response to terrain forcing, transient behavior in time and space, and adherence to simplified theoretical models were examined. The turbulence structure in these stably stratified boundary layers was also investigated. Numerical modeling is the main tool in this thesis; observations are used primarily to ensure a realistic model behavior.</p><p>Simple shallow-water theory provides a useful framework for analyzing high-velocity flows along mountainous coastlines, but for an unexpected reason. Waves are trapped in the inversion by the curvature of the wind-speed profile, rather than by an infinite stability in the inversion separating two neutral layers, as assumed in the theory. In the absence of blocking terrain, observations of steady-state supercritical flows are not likely, due to the diurnal variation of flow criticality.</p><p>In many simplified models, non-local processes are neglected. In the flows studied here, we showed that this is not always a valid approximation. Discrepancies between simulated katabatic flow and that predicted by an analytical model are hypothesized to be due to non-local effects, such as surface inhomogeneity and slope geometry, neglected in the theory. On a different scale, a reason for variations in the shape of local similarity scaling functions between studies is suggested to be differences in non-local contributions to the velocity variance budgets.</p>

Simple models of transpiration, e.g., the Penman-Monteith equation, treat atmospheric conditions as driving variables. In fact, transpiration modifies temperature and humidity throughout the convective boundary layer, creating feedbacks that stabilize the water use of vegetation. This thesis concentrates on the new empirical relationships proposed by Monteith (1995), for developing simple models of feedback, and then applies these relationships to data from the Oregon Cascades. Monteith showed that there is strong laboratory evidence to support a linear relationship between leaf transpiration rate and leaf conductance. If this relationship holds for vegetation in the field, simple models to explain the diurnal variation of canopy conductance can be developed. When this model was applied to data from a Douglas fir forest, canopy conductance changed in response to transpiration rate, rather than to saturation deficit, as has been previously assumed. Monteith also reanalyzed data from McNaughton and Spriggs (1989) which explored the dependence of the Priestley-Taylor coefficient alpha on surface parameters. He showed that there is a linear relationship between alpha and surface conductance. By combining this "demand function" with the physiological "supply function" described earlier, the PMPT model is developed in which evaporation rate depends on physical feedbacks in the convective boundary layer and physiological feedbacks within plants. The thesis will focus on the results of the research done using this model. The PMPT model will then be compared with other simple models of transpiration in order to determine its applicability. / Graduation date: 1997

Graduation date: 1991

Weak-wind flow in the nocturnal boundary is one of the most poorly understood problems in the field of meteorology. The understanding of weak-wind flows is essential for the improvement of regulatory dispersion models which are currently rendered invalid under weak-wind conditions and stable stratification. Recently there have been increased efforts directed towards improving the understanding nocturnal boundary layer dynamics. The results of these studies have shown that nocturnal boundary layer flows are often dominated by intermittent turbulence and motions occurring on horizontal scales ranging from hundreds of meters to several kilometers and on time scales of 1 minute to 1 hour. We refer to these scales as sub-meso. This connection has led to the hypothesis that intermittent turbulence generation may be the result of sub-meso motions that are subject to external forcing originating in the deeper boundary layer. However, these processes have proven difficult to measure as traditional sensor networks have failed to provide the vertical and horizontal coverage necessary to observe the driving forces on these scales. This study sought to close this knowledge gap using SOund Detection And Ranging (SODAR). SODAR is a ground based acoustic remote sensing technology that is capable of measuring wind and turbulence at multiple heights in the boundary layer. Data were collected with a pair of SODAR systems with sequentially increasing separation distance at the Oregon State University Botany and Plant Pathology lab during the summer of 2010. The data have indicated that motion occurring on time scales of 2 minutes to 32 minutes are isolated to the lowest 50 meters of the nocturnal boundary layer. Surface-layer measurements were collected using a pair of sonic anemometers placed at heights of 1.5 and 7 meters above ground level. Comparisons of surface-layer measurements and deeper boundary layer measurements have shown that when the surface layer stratification is stable, processes within the surface layer are not likely to be influenced by external forcing from aloft. In contrast external forcing from the deeper boundary layer may still have an influence on weak, nocturnal surface flows when the surface layer is weakly stratified as is shown for the case of low-level jets. / Graduation date: 2013

Bradford Howland, Walter H. Pits, and Robert C. Gesteland. / "September 21, 1962." / Bibliography: p. 28. / Army Signal Corps Contract DA36-039- sc-78108. Dept. of the Army Task 3-99-20-001 and Project 3-99-00-000. Signal Corps Contract DA-SIG-36-039-61-G14. U.S. Air Force Contract AF33(616)-7783. National Institute of Health Grant B-2480(C1)

Thesis (Sc. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1983. / Cover title: Flow and skin friction over natural rough beds. Includes bibliographical references (p. 325-333).