Since its introduction in 1997, the use of Detached Eddy Simulation (DES) and similar hybrid turbulence techniques has become increasingly popular in the field of CFD. However, with increased use some of the limitations of the DES model have become apparent. One of these is the dependence of DES on grid construction, particularly regarding the point of transition between the Reynolds-Averaged Navier-Stokes and Large Eddy Simulation models. An additional issue that arises with unstructured grids is the definition of the grid spacing in the implementation of a DES length scale. To lay the ground work to study these effects the Spalart-Allmaras one-equation turbulence model, SA based DES hybrid turbulence model, and the Scale Adaptive Simulation hybrid turbulence model are implemented in an unstructured grid CFD code, UNCLE. The implemented SA based DES model is validated for flow over a three-dimensional circular cylinder for three different turbulent Reynolds numbers. Validation included studying the pressure, skin friction coefficient, centerline velocity distributions averaged in time and space. Tools to output the mean velocity profiles and Reynolds stresses were developed. A grid generation code was written to generate a two/three dimensional circular cylinder grid to simulate flow over the cylinder in UNCLE. The models implemented and validated, and the additional tools mentioned will be used in the future.

Thesis(M.S.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references.

Aim of this diploma thesis is calculating the carpet area/built-up area coefficient and make a proposal how to put this coefficient in place in building evaluation field. Also, assessment of error rate of this method is needed. More methods were suggested based on differently calculated coefficients. Comparison of different sources of public information about buildings was made and these were compared to actual state of the buildings. Research was made whether there is correlation between age of the building and tipical building´s characteristics in examined area. Studied area is called Kluky (part of Hradec Králové).

The master´s thesis deals with influence of the insulation of the detached house on the costs associated with heating and the effect on the usual price of detached house. In the theoretical part of the thesis are given the basic concepts of heat, the topic of energy intensity of buildings, methods of thermal insulation, types of thermal insulation, the development of thermal properties of burnt brickwork and valuation. In the practical part there are designed variants of economy measures and there are calculations of heat losses of the current state and newly proposed variants. Then follows the energy savings assessment, payback period and the effect on the price of a usual detached house.

The master’s thesis topic is a project of a low-energy cottage. The cottage is situated in Kralický Sněžník near Jeseník and it is designed for forty customers. The house is designed as a detached house with two floors and with one basement and with a gable roof. A substructure is from a system blockpanel of a concrete and a heat insulations. The structural system of a superstructure is designed from a timber frame and a heat insulations. The indoor shell is formed from a plasterboard. The house shell is covered by heat insulations. The main entrance is located to the south. It leads to a hall with a reception. On the ground floor we can find a restaurant which is situated in the left part of the cottage. On the ground floor we can also find a room for disabled people and in the north-eastern corner are situated WC for people. The first floor is reachable via stairs from the entry hall. Upstairs there are seven rooms and four bathrooms with toilets. Two rooms of them have a ensuite bathroom. All of the rooms are enterable from the hall. Five of them have a window to the south side and other two rooms have a window to the north side. In the basement there is an utility room a boiler room a laundry a workshop and stocks.

The increase of standard of living in Bata´s semi-detached house in the district Letná in Zlín.

<P> The work presented m this thesis focused on using the hybrid Unsteady Reynolds-Averaged Navier-Stokes (URANS)/Large Eddy Simulation (LES) methodology to investigate the flow pulsation phenomenon in compound rectangular channels for isothermal flows. The specific form of the hybrid URANS/LES approach that was used is the Strelets (2001) version of the Detached Eddy Simulation (DES). It is of fundamental interest to study the problem of flow pulsations, as it is one of the most important mechanisms that directly affect the heat transfer occurring in sub-channel geometries such as those in nuclear fuel bundles. The predictions associated with the heat transfer and fluid flow in sub-channel geometry can be used to develop simplified physical models for sub-channel mixing for use in broader safety analysis codes. The primary goal of the current research work was to determine the applicability of the DES approach to predict the flow pulsations in sub-channel geometries. It was of interest to see how accurately the dynamics associated with the flow pulsations can be resolved from a spatial-temporal perspective using the specific DES model. The research work carried out for this thesis was divided into two stages. </p> <p> In the first stage of the research work, effort was concentrated to primarily understand the field of sub-channel flow pulsations and its implications from both an experimental and numerical point of view. It was noted that unsteady turbulence modeling approaches have great potential in providing insights into the fundamentals of sub-channel flow pulsations. It was proposed that for this thesis work, the Shear Stress Transport (SST) based DES model be used to understand the dynamics associated with sub-channel flow pulsations. To the author's knowledge the DES-SST based turbulence model has never been used for resolving the effects of sub-channel flow pulsations. Next, the hybrid URANS/LES turbulence modeling technique was reviewed in great detail to understand the philosophy of the hybrid URANS/LES technique and its ability to resolve fundamental flows of interest. Effort was directed to understand the switching mechanism (which blends the URANS region with the LES region) in the DES-SST model for fully wall bounded turbulent flows without boundary layer separation. To the author's knowledge, the DES-SST model has never been used on a fully wall bounded turbulent flow problem without boundary layer separation. Thus, the DES-SST model was first completely validated for a fully developed turbulent channel flow problem without boundary layer separation. </p> <p> In the second stage of the research work, the DES-SST model was used to study the flow pulsation phenomena on two rectangular sub-channels connected by a gap, on which extensive experiments were conducted by Meyer and Rehme (1994). It was found that the DES-SST model was successful in resolving significant portion of the flow field in the vicinity of the gap region. The span-wise velocity contours, velocity vector plots, and time traces of the velocity components showed the expected cross flow mixing between the sub-channels through the gap. The predicted turbulent kinetic energy showed two clear peaks at the edges of the gap. The dynamics of the flow pulsations were quantitatively described through temporal auto-correlations, spatial cross-correlations and power spectral functions. The numerical predictions were in general agreement with the experiments in terms of the quantitative aspects. From an instantaneous time scale point of view, the DES-SST model was able to identify different flow mixing patterns. The pulsating flow is basically an effect of the variation of the pressure field which is a response to the instability causing the fluid flow pulsations. Coherent structures were identified in the flow field to be comprised of eddies, shear zones and streams. Eddy structures with high vorticity and low pressure cores were found to exist near the vicinity of the gap edge region. A three dimensional vorticity field was identified and found to exist near the gap edge region. The instability mechanism and the probable cause behind the quasi-periodic fluid flow pulsations was identified and related to the inflectional stream-wise velocity profile. Simulations were also performed with two different channel lengths in comparison to the reference channel length. Different channel length studies showed similar statistical description of the flow field. However, frequency independent results were not obtained. In general, simulations performed using the DES-SST model were successful in capturing the effects of the fluid flow pulsations. This modeling technique has great potential to be used for actual rod bundle configurations. </p> / Thesis / Doctor of Philosophy (PhD)

Recent design trends in steam turbines strive for high aerodynamic loading and high aspect ratio to meet the demand of higher efficiency. These design trends together with the low structural frequency in last stage steam turbines increase the susceptibility of the turbine blades to flutter. Flutter is the self-excited and self-sustained aeroelastic instability phenomenon, which can result in rapid growth of blade vibration amplitude and eventually blade failure in a short period of time unless adequately damped. To prevent the occurrences of flutter before the operation of new steam turbines, a compromise between aeroelastic stability and stage efficiency has to be made in the steam turbine design process. Due to the high uncertainty in present flutter prediction methods, engineers use large safety margins in predicting flutter which can rule out designs with higher efficiency. The ability to predict flutter more accurately will allow engineers to push the design envelope with greater confidence and possibly create more efficient steam turbines. The present work aims to investigate the influence of tip clearance flow on the prediction of steam turbine flutter characteristics. Tip clearance flow effect is one of the critical factors in flutter analysis for the majority of aerodynamic work is done near the blade tip. Analysis of the impact of tip clearance flow on steam turbine flutter characteristics is therefore needed to formulate a more accurate aeroelastic stability prediction method in the design phase.Besides the tip leakage vortex, the induced vortices in the tip clearance flow can also influence blade flutter characteristics. However, the spatial distribution of the induced vortices cannot be resolved by URANS method for the limitation of turbulence models. The Detached-Eddy Simulation (DES) calculation is thus applied on a realistic-scale last stage steam turbine model to analyze the structure of induced vortices in the tip region. The influence of the tip leakage vortex and the induced vortices on flutter prediction are analyzed separately. The KTH Steam Turbine Flutter Test Case is used in the flutter analysis as a typical realistic-scale last stage steam turbine model. The energy method based on 3D unsteady CFD calculation is applied in the flutter analysis. Two CFD solvers, an in-house code LUFT and a commercial software ANSYS CFX, are used in the flutter analysis as verification of each other. The influence of tip leakage vortex on the steam turbine flutter prediction is analyzed by comparing the aeroelastic stability of two models: one with the tip gap and the other without the tip gap. Comparison between the flutter characteristics predicted by URANS and DES approaches is analyzed to investigate the influence of the induced vortices on blade flutter characteristics. The multiple induced vortices and their relative rotation around the tip leakage vortex in the KTH Steam Turbine Flutter Test Case are resolved by DES but not by URANS simulations. Both tip leakage vortex and induced vortices have an influence on blade loading on the rear half of the suction side near the blade tip. The flutter analysis results suggest that the tip clearance flow has a significant influence on blade aerodynamic damping at the least stable interblade phase angle (IBPA), while its influence on the overall shape of the damping curve is minor. At the least stable IBPA, the tip leakage vortex shows a stabilization effect on rotor aeroelastic stabilities while the induced vortices show a destabilization effect on it. Meanwhile, a non-linear unsteady flow behavior is observed due to the streamwise motion of induced vortices during blade oscillation, which phenomenon is only resolved in DES results.

Detached Eddy Simulations (DES) is a hybrid URANS-LES technique that was proposed to obtain computationally feasible solutions of high Reynolds number flows undergoing massive separation with reliable accuracy. Since its inception, DES has been applied to a wide variety of flow fields, but mostly limited to unbounded external aerodynamic flows. This is the first study to apply and validate DES to predict the internal flow and heat transfer in non-canonical flows of industrial relevance. The prediction capabilities of DES in capturing the effects of Coriolis forces, which are induced by rotation, and centrifugal buoyancy forces, which are induced by thermal gradients, are also authenticated. The accurate prediction of turbulent flows is sensitive to the level of turbulence predicted by the turbulence scheme. By treating the regions of interest in LES mode, DES allows the unsteadiness in these regions to develop and hence predicts the turbulence levels accurately. Additionally, this permits DES to capture the effects of system rotation and buoyancy. Computations on a rotating system (a sudden expansion duct) and a system subjected to thermal gradients (cavity with a heated wall) validate the prediction capability of DES. The application of DES is further extended to a non-canonical, internal flow which is of relevance in internal cooling of gas turbine blades. Computations of the fully developed flow and heat transfer shows that DES surpasses several shortcomings of the RANS model on which it is based. DES accurately predicts the primary and secondary flow features, the turbulence characteristics and the heat transfer in stationary ducts and in rotating ducts, where the effects of Coriolis forces and centrifugal buoyancy forces are dominant. DES computations are carried out at a computational cost that is almost an order of magnitude less than the LES with little compromise on the accuracy. However, the capabilities of DES in predicting the transition to turbulence are inadequate, as highlighted by the flow features and the heat transfer in the developing region of the duct. But once the flow becomes fully turbulent, DES predicts the flow physics and shows good quantitative agreement with the experiments and LES. / Ph. D.

<p dir="ltr">The computational campaign reported in this thesis focuses on a series of experiments at Mach 2.85 carried out in the 1980s at NASA Ames Research Center on a set of cylinder / skewed flare configurations designed to produce highly three-dimensional shockwave / boundary-layer interactions in the absence of end-wall effects. Computations carried out in that era were unable to match the experimental results using the numerical techniques, turbulence models, and grid resolution available at the time. In the present work, newer Reynolds-averaged Navier-Stokes and detached eddy simulation methods have been applied to these flows, and relatively good agreement has been obtained with the experimental data. Difficulty in capturing the correct separation bubble size was encountered with initial detached eddy simulations, but the introduction of resolved turbulence via a boundary layer trip produced much better results. This thesis reports on results obtained for four inclination angles (0 deg, 5 deg, 10 deg, and 23 deg) of the skewed flare. Detached eddy simulation is seen to be an economical alternative to large eddy simulation for capturing many features of large-scale separation unsteadiness over long time intervals at true Reynolds number.</p>