On the anomaly of velocity-pressure decoupling in collocated mesh solutions

The use of various pressure correction algorithms originally developed for fully staggered meshes can yield a velocity-pressure decoupled solution for collocated meshes. The mechanism that causes velocity-pressure decoupling is identified. It is shown that the use of a partial differential equation for the incremental pressure eliminates such a mechanism and yields a velocity-pressure coupled solution. Example flows considered are a three dimensional lid-driven cavity flow and a laminar flow through a 90 deg bend square duct. Numerical results obtained using the collocated mesh are in good agreement with the measured data and other numerical results

A numerical study of chemically reacting flow in nozzles

The space station uses small rocket motors, called thrusters, for orientation control. Because of the lack of viable design tools for small rockets, the initial thruster design was basically a very small version of a large rocket motor. Thrust measurements of the initial design were lower than predicted. To improve predictions it was decided to develop a verison of the RPLUS2D reacting flow code for thruster calculations. RPLUS2D employs an implicit finite volume, lower-upper symmetric successive overrelaxation (LU-SSOR) scheme for solving the complete two-dimensional Navier-Stokes equations and species transport equations in a coupled and very efficient manner. The combustion processes are modeled by a 9-species, 18 step finite-rate chemistry model, and the turbulence is simulated by a Baldwin-Lomax algebraic model. The code is extended to handle multiple subsonic inlet conditions where the total mass flow is governed by conditions calculated at the thruster-throat. Results are shown for a thruster design where the overall mixture ratio is hydrogen rich. A calculation of a large area ratio divergent nozzle is also presented

Improved Modeling of Finite-Rate Turbulent Combustion Processes in Research Combustors

The objective of this thesis is to further develop and test a stochastic model of turbulent combustion in recirculating flows. There is a requirement to increase the accuracy of multi-dimensional combustion predictions. As turbulence affects reaction rates, this interaction must be more accurately evaluated. In this work a more physically correct way of handling the interaction of turbulence on combustion is further developed and tested. As turbulence involves randomness, stochastic modeling is used. Averaged values such as temperature and species concentration are found by integrating the probability density function (pdf) over the range of the scalar. The model in this work does not assume the pdf type, but solves for the evolution of the pdf using the Monte Carlo solution technique. The model is further developed by including a more robust reaction solver, by using accurate thermodynamics and by more accurate transport elements. The stochastic method is used with Semi-Implicit Method for Pressure-Linked Equations. The SIMPLE method is used to solve for velocity, pressure, turbulent kinetic energy and dissipation. The pdf solver solves for temperature and species concentration. Thus, the method is partially familiar to combustor engineers. The method is compared to benchmark experimental data and baseline calculations. The baseline method was tested on isothermal flows, evaporating sprays and combusting sprays. Pdf and baseline predictions were performed for three diffusion flames and one premixed flame. The pdf method predicted lower combustion rates than the baseline method in agreement with the data, except for the premixed flame. The baseline and stochastic predictions bounded the experimental data for the premixed flame. The use of a continuous mixing model or relax to mean mixing model had little effect on the prediction of average temperature. Two grids were used in a hydrogen diffusion flame simulation. Grid density did not effect the predictions except for peak temperature and tangential velocity. The hybrid pdf method did take longer and required more memory, but has a theoretical basis to extend to many reaction steps which cannot be said of current turbulent combustion models

A numerical study of the hot gas environment around a STOVL aircraft in ground proximity

The development of Short Takeoff Vertical Landing (STOVL) aircraft has historically been an empirical- and experienced-based technology. A 3-D turbulent flow CFD code was used to calculate the hot gas environment around an STOVL aircraft operating in ground proximity. Preliminary calculations are reported for a typical STOVL aircraft configuration to identify key features of the flow field, and to demonstrate and assess the capability of current 3-D CFD codes to calculate the temperature of the gases ingested at the engine inlet as a function of flow and geometric conditions

Pressure Control for Low Earth Orbit Investigated

There is renewed interest in cryogenic oxygen storage for an advanced second-generation orbital maneuvering system and reaction control systems in a low Earth orbit because cryogenic propellants are more energetic and environmentally friendly than current storable propellants. Unfortunately, heat transfer or heat leak into these storage systems increases tank pressure. On Earth, pressure is easily controlled by venting from the gaseous, or ullage, space above the liquid. In low gravity, the location of vapor is unknown and direct venting would expel liquid. Historically, upper stages have used auxiliary thrusters to resettle the tank contents and fix the location of the ullage space in orbit

Eindrapport Ieper - Ieperlee Lot 2B Fase 2

Dit rapport werd ingediend bij het agentschap samen met een aantal afzonderlijke digitale bijlagen. Een aantal van deze bijlagen zijn niet inbegrepen in dit pdf document en zijn niet online beschikbaar. Sommige bijlagen (grondplannen, fotos, spoorbeschrijvingen, enz.) kunnen van belang zijn voor een betere lezing en interpretatie van dit rapport. Indien u deze bijlagen wenst te raadplegen kan u daarvoor contact opnemen met: [email protected]

Rapid evolution of thermal tolerance in the water flea Daphnia

Global climate is changing rapidly, and the degree to which natural populations respond genetically to these changes is key to predicting ecological responses. So far, no study has 25 documented evolutionary changes in the thermal tolerance of natural populations as a response to recent temperature increase. Here, we demonstrate genetic change in the capacity to tolerate higher temperatures in the water flea Daphnia using both a selection experiment and the reconstruction of evolution over a period of forty years using a layered dormant egg bank. We observed a genetic increase in thermal tolerance in response to a two-year ambient + 4 °C selection treatment and in the genotypes of natural populations from the 1960s and 2000s hatched from lake sediments. This demonstrates that natural populations have evolved increased tolerance to higher temperatures, likely associated with increased frequency of heat waves over the past decades, and possess the capacity to evolve increased tolerance to future warming.status: publishe

Data from :Insight into the durability of plant resistance to aphids from a demo-genetic study of Aphis gossypii in melon crops

Dryad digital repository http://datadryad.org/resource/doi:10.5061/dryad.gf54qil s'agit d'un type de produit dont les métadonnées ne correspondent pas aux métadonnées attendues dans les autres types de produit : REPORTData from :Insight into the durability of plant resistance to aphids from a demo-genetic study of Aphis gossypii in melon crop