Dynamic flow distortion investigation in an S-duct using DDES and SPIV data

The dynamic flow distortion generated within convoluted aero-engine intakes can affect the performance and operability of the engine. There is a need for a better understanding of the main flow mechanisms which promote flow distortion at the exit of S-shaped intakes. This paper presents a detailed analysis of the main coherent structures in an S-duct flow field based on a Delayed Detached Eddy Simulation (DDES). The DDES capability to capture the characteristics of the highly unsteady flow field is demonstrated against high resolution, synchronous Stereoscopic Particle Image Velocimetry (SPIV) measurements at the Aerodynamic Interface Plane (AIP). The flow field mechanisms responsible for the main AIP perturbations are identified. Clockwise and counter-clockwise stream-wise vortices are alternately generated around the separation region at a frequency of St=0.53, which promotes the swirl switching at the AIP. Spanwise vortices are also shed from the separation region at a frequency of St=1.06, and convect downstream along the separated centreline shear layer. This results in a vertical modulation of the main loss region and a fluctuation of the velocity gradient between the high and low velocity flow at the AIP

Automatic eduction and statistical analysis of coherent structures in the wall region of a confine plane

This paper describes a vortex detection algorithm used to expose and statistically characterize the coherent flow patterns observable in the velocity vector fields measured by Particle Image Velocimetry (PIV) in the impingement region of air curtains. The philosophy and the architecture of this algorithm are presented. Its strengths and weaknesses are discussed. The results of a parametrical analysis performed to assess the variability of the response of our algorithm to the 3 user-specified parameters in our eduction scheme are reviewed. The technique is illustrated in the case of a plane turbulent impinging twin-jet with an opening ratio of 10. The corresponding jet Reynolds number, based on the initial mean flow velocity U0 and the jet width e, is 14000. The results of a statistical analysis of the size, shape, spatial distribution and energetic content of the coherent eddy structures detected in the impingement region of this test flow are provided. Although many questions remain open, new insights into the way these structures might form, organize and evolve are given. Relevant results provide an original picture of the plane turbulent impinging jet

Numerical investigation of high-pressure combustion in rocket engines using Flamelet/Progress-variable models

The present paper deals with the numerical study of high pressure LOx/H2 or LOx/hydrocarbon combustion for propulsion systems. The present research effort is driven by the continued interest in achieving low cost, reliable access to space and more recently, by the renewed interest in hypersonic transportation systems capable of reducing time-to-destination. Moreover, combustion at high pressure has been assumed as a key issue to achieve better propulsive performance and lower environmental impact, as long as the replacement of hydrogen with a hydrocarbon, to reduce the costs related to ground operations and increase flexibility. The current work provides a model for the numerical simulation of high- pressure turbulent combustion employing detailed chemistry description, embedded in a RANS equations solver with a Low Reynolds number k-omega turbulence model. The model used to study such a combustion phenomenon is an extension of the standard flamelet-progress-variable (FPV) turbulent combustion model combined with a Reynolds Averaged Navier-Stokes equation Solver (RANS). In the FPV model, all of the thermo-chemical quantities are evaluated by evolving the mixture fraction Z and a progress variable C. When using a turbulence model in conjunction with FPV model, a probability density function (PDF) is required to evaluate statistical averages of chemical quantities. The choice of such PDF must be a compromise between computational costs and accuracy level. State- of-the-art FPV models are built presuming the functional shape of the joint PDF of Z and C in order to evaluate Favre-averages of thermodynamic quantities. The model here proposed evaluates the most probable joint distribution of Z and C without any assumption on their behavior.Comment: presented at AIAA Scitech 201

Tidal Energy and Coastal Models: Improved Turbine Simulation

Marine renewable energy is a continually growing topic of both commercial and academic research sectors. While not as developed as other renewable technologies such as those deployed within the wind sector, there is substantial technological crossover coupled with the inherent high energy density of water, that has helped push marine renewables into the wider renewable agenda. Thus, an ever expanding range of projects are in various stages of development.As with all technological developments, there are a range of factors that can con-tribute to the rate of development or eventual success. One of the main difficulties, when looking at marine renewable technologies in a comparative view to other en-ergy generation technologies, is that the operational environment is physically more complex: Energy must be supplied in diverse physical conditions, that temporally fluctuate with a range of time scales. The constant questions to the iteration to the local ecology. The increased operational fatigue of deployed devices. The financial risk associated within a recent sector.This work presents the continual research related to the computational research development of different marine renewable technologies that were under develop-ment of several institutional bodies at the time of writing this document.The scope has a wide envelopment as the nature of novel projects means that the project failure rate is high. Thus, forced through a combination of reasons related to financial, useful purpose and intellectual property, the research covers distinct projects

Numerical simulation and characterization of jet flows in indoor environments

Jet flows are prevalent in indoor environment and other engineering applications. Typical examples in indoor environment include the flow discharged from personal ventilation systems, and the jet exhaled through breathing or coughing. When there is density (or temperature) difference between the jet and surroundings, jet flow becomes stratified jet. Due to its complication, stratified jet flow is difficult to model, especially in the developing or transitional region of the flow. Studying stratified jet flows is of great significance for understanding the mixing dynamics of jet and ambient environment. This is particularly important for optimizing indoor environment design, or obtaining accurate boundary conditions in indoor air flow simulations.^ Various turbulence models have been used to simulate stratified flows. This investigation systematically evaluated the performance of seven turbulence models under different turbulence levels and stratification levels, by comparing simulation results with experimental data. Mean velocity, turbulent kinetic energy and turbulent shear stress were examined in the comparisons. Mean square error values were used to quantify the evaluation. For the weakly stratified jet, all seven models could predict well the mean velocity, but for the strongly stratified jet, the Reynolds stress model and LES overpredicted the velocity in the unstable stratification region. SST k-ω was the overall best model. This investigation also analyzed the computing costs of the models as well as the vorticity and entrainment ratios predicted in the simulation.^ This study introduced a new dynamic turbulent Schmidt number model which can determine turbulent Schmidt number based on local flow structure. The proposed model can improve the prediction of density distribution especially at downstream locations, although it takes 10% additional computing time. ^ Furthermore, this study developed a CFD model to investigate gasper-induced jet flow. The results indicated that the jet centerline velocity profile could collapse into a universal curve after normalization; meanwhile, the lateral velocity profiles at downstream locations followed self-similarity rule. Based on that, the study proposed two models to predict normalized velocity at jet centerline, and lateral velocity at downstream locations, respectively. A flow rate model was also developed to predict the mainstream flow rates at various downstream locations of gasper-induced jet. The CFD model and developed flow rate model were further used to assess the impact of gasper on air quality in the breathing zones of passengers