Author: Ferran Marti Duran
Publisher:
ISBN: 9781267815934
Category :
Languages : en
Pages : 104
Book Description
In this thesis, we develop and test an experimental apparatus capable of examining the effect of turbulence on the evaporation of droplets when the Kolmogorov scale is smaller than the size of the drop (where size refers to the nominal droplet diameter). Traveling drop and suspended drop cases have been studied experimentally and the evaporation rate has also been predicted based on classical computations of transport rates. Cases involving still air, a mean flow with turbulence, and a mean flow without turbulence have been tested. The experimental data matches the theoretical computations for the case of still air and mean flow with no turbulence. There is no accepted computational model that can account for turbulent flow, but the experimental conditions tested so far do not show any measurable effect of turbulence on the evaporation rate. These findings suggest that turbulence is a much smaller factor in evaporation than is mean flow over the droplet. Hence, one suggestion for future work is to study traveling droplets with zero relative velocity to the air in order to focus the analysis on the effects of turbulence with no mean flow.
Droplet Evaporation in an Active Turbulence Grid Wind Tunnel
Author: Ferran Marti Duran
Publisher:
ISBN: 9781267815934
Category :
Languages : en
Pages : 104
Book Description
In this thesis, we develop and test an experimental apparatus capable of examining the effect of turbulence on the evaporation of droplets when the Kolmogorov scale is smaller than the size of the drop (where size refers to the nominal droplet diameter). Traveling drop and suspended drop cases have been studied experimentally and the evaporation rate has also been predicted based on classical computations of transport rates. Cases involving still air, a mean flow with turbulence, and a mean flow without turbulence have been tested. The experimental data matches the theoretical computations for the case of still air and mean flow with no turbulence. There is no accepted computational model that can account for turbulent flow, but the experimental conditions tested so far do not show any measurable effect of turbulence on the evaporation rate. These findings suggest that turbulence is a much smaller factor in evaporation than is mean flow over the droplet. Hence, one suggestion for future work is to study traveling droplets with zero relative velocity to the air in order to focus the analysis on the effects of turbulence with no mean flow.
Publisher:
ISBN: 9781267815934
Category :
Languages : en
Pages : 104
Book Description
In this thesis, we develop and test an experimental apparatus capable of examining the effect of turbulence on the evaporation of droplets when the Kolmogorov scale is smaller than the size of the drop (where size refers to the nominal droplet diameter). Traveling drop and suspended drop cases have been studied experimentally and the evaporation rate has also been predicted based on classical computations of transport rates. Cases involving still air, a mean flow with turbulence, and a mean flow without turbulence have been tested. The experimental data matches the theoretical computations for the case of still air and mean flow with no turbulence. There is no accepted computational model that can account for turbulent flow, but the experimental conditions tested so far do not show any measurable effect of turbulence on the evaporation rate. These findings suggest that turbulence is a much smaller factor in evaporation than is mean flow over the droplet. Hence, one suggestion for future work is to study traveling droplets with zero relative velocity to the air in order to focus the analysis on the effects of turbulence with no mean flow.
On the Generation of Unsteady Mean and Turbulent Flows in a Wind Tunnel Using an Active Grid
Author: Abdullah Azzam
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
Unsteady flows are pervasive in nature and engineering applications such as UAVs. Simulating these flows in an experimental setting is key to avoiding detrimental changes in the performance of such applications. This study explores the capabilities of an active grid in producing unsteady flows in a recirculating wind tunnel. The grid is operated in different modes that allow control over the flow frequency, amplitude and turbulence intensity. Hot-wire measurements demonstrate the grid's capabilities in generating flows typical of those used in experiments of unsteady aerodynamics. Mean grid blockage, freestream speed and tunnel size were all found to be factors influencing the resulting flow. The response of turbulence to the oscillating flow was also investigated and results showed a modulation of the turbulence intensity and dissipation rate that is dependent on the frequency of the imposed oscillations. A change in the scaling behaviour of the dissipation rate was also noted.
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
Unsteady flows are pervasive in nature and engineering applications such as UAVs. Simulating these flows in an experimental setting is key to avoiding detrimental changes in the performance of such applications. This study explores the capabilities of an active grid in producing unsteady flows in a recirculating wind tunnel. The grid is operated in different modes that allow control over the flow frequency, amplitude and turbulence intensity. Hot-wire measurements demonstrate the grid's capabilities in generating flows typical of those used in experiments of unsteady aerodynamics. Mean grid blockage, freestream speed and tunnel size were all found to be factors influencing the resulting flow. The response of turbulence to the oscillating flow was also investigated and results showed a modulation of the turbulence intensity and dissipation rate that is dependent on the frequency of the imposed oscillations. A change in the scaling behaviour of the dissipation rate was also noted.
Droplet Vaporization in Turbulent Flow
Author: Jung-Kyu Park
Publisher:
ISBN:
Category :
Languages : en
Pages : 382
Book Description
Publisher:
ISBN:
Category :
Languages : en
Pages : 382
Book Description
Generation of Atmospheric Turbulence in a Wind Tunnel
Author: Elena Muñiz Pladellorens
Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
This report aims to contribute to the knowledge and characterization of grid generated turbulence in a wind tunnel. It starts with a theory introduction to turbulence where we bring together the classic approaches (Richardson-Kolmogorov equilibrium cascade) and more recent research. The latter includes the nonequilibrium dissipation law developed by [Valente and Vassilicos, 2011] and calculus methods such as set forth by [Puga and LaRue, 2017]. The study is based on two grids: an active grid in two different modes (open and random) and a regular and irregular passive grids. In terms of the means employed, the data is gathered using a hot-wire anemometer which makes it possible to have a high time resolution even though only one point and 1D turbulence is collected. In addition, the software used in the mathematical processing is MATLAB. The crucial parameters analyzed are the variations, the lengthscales (as well as their interaction) and dissipation rate constants, both equilibrium and nonequilibrium definitions. Some significant results have been found. In the first place Kolmogorov hypotheses are justified to hold true. Furthermore, there are some signs that the nonequilibrium law seems a plausible answer to some instabilities perceived. Finally, the vertical profiles of the irregular grid clearly show that the turbulence generated is inhomogeneous, which ushers in new lines of investigation.
Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
This report aims to contribute to the knowledge and characterization of grid generated turbulence in a wind tunnel. It starts with a theory introduction to turbulence where we bring together the classic approaches (Richardson-Kolmogorov equilibrium cascade) and more recent research. The latter includes the nonequilibrium dissipation law developed by [Valente and Vassilicos, 2011] and calculus methods such as set forth by [Puga and LaRue, 2017]. The study is based on two grids: an active grid in two different modes (open and random) and a regular and irregular passive grids. In terms of the means employed, the data is gathered using a hot-wire anemometer which makes it possible to have a high time resolution even though only one point and 1D turbulence is collected. In addition, the software used in the mathematical processing is MATLAB. The crucial parameters analyzed are the variations, the lengthscales (as well as their interaction) and dissipation rate constants, both equilibrium and nonequilibrium definitions. Some significant results have been found. In the first place Kolmogorov hypotheses are justified to hold true. Furthermore, there are some signs that the nonequilibrium law seems a plausible answer to some instabilities perceived. Finally, the vertical profiles of the irregular grid clearly show that the turbulence generated is inhomogeneous, which ushers in new lines of investigation.
The Evaporation of Liquid Droplets in Highly Turbulent Gas Streams
Author: Richard Gould
Publisher:
ISBN:
Category :
Languages : en
Pages : 8
Book Description
Single acetone and heptane droplets were suspended from a hypodermic needle in turbulent airflow, and the Nusselt number was obtained from direct measurements of the droplet diameter and evaporation rate. Acetone was selected because it fluoresces when irradiated with ultraviolet laser radiation while heptane was selected because of its high volatility compared with water, methanol, and ethanol which were used previously. Planar laser induced fluorescence (PLIF) measurements were made to obtain qualitative concentration measurements of gaseous acetone in the boundary layer surrounding the droplet. The goal of these measurements was to give insight as to why the evaporation rate is increased by 50 % when the gas phase turbulence is increased from the laminar flow case to the case where the freestream turbulence is 10%. The use of acetone droplets required that the influence of humidity on droplet evaporation rate be considered. Measurements of the turbulence intensity of heated freestream air were also made. Finally, many modifications to improve the experimental apparatus were made during this research project.
Publisher:
ISBN:
Category :
Languages : en
Pages : 8
Book Description
Single acetone and heptane droplets were suspended from a hypodermic needle in turbulent airflow, and the Nusselt number was obtained from direct measurements of the droplet diameter and evaporation rate. Acetone was selected because it fluoresces when irradiated with ultraviolet laser radiation while heptane was selected because of its high volatility compared with water, methanol, and ethanol which were used previously. Planar laser induced fluorescence (PLIF) measurements were made to obtain qualitative concentration measurements of gaseous acetone in the boundary layer surrounding the droplet. The goal of these measurements was to give insight as to why the evaporation rate is increased by 50 % when the gas phase turbulence is increased from the laminar flow case to the case where the freestream turbulence is 10%. The use of acetone droplets required that the influence of humidity on droplet evaporation rate be considered. Measurements of the turbulence intensity of heated freestream air were also made. Finally, many modifications to improve the experimental apparatus were made during this research project.
Effect of Turbulence on Droplet Evaporation and Drag
Author: Carlos Pereira Salvador
Publisher:
ISBN:
Category :
Languages : en
Pages : 320
Book Description
Publisher:
ISBN:
Category :
Languages : en
Pages : 320
Book Description
The Effect of Stable Stratification on Decaying Grid-generated Turbulence
Author: Kyunghwan Yoon
Publisher:
ISBN:
Category : Turbulence
Languages : en
Pages : 362
Book Description
Publisher:
ISBN:
Category : Turbulence
Languages : en
Pages : 362
Book Description
Grid Effects Upon the Power-density Spectrum of Wind Tunnel Turbulence
Author: Timothy Leonard Vogt
Publisher:
ISBN:
Category :
Languages : en
Pages : 48
Book Description
Publisher:
ISBN:
Category :
Languages : en
Pages : 48
Book Description
Computations of Turbulent Droplet Dispersion for Wind Tunnel Icing Tests
Author: Brian Charles DeAngelis
Publisher:
ISBN:
Category :
Languages : en
Pages : 246
Book Description
Publisher:
ISBN:
Category :
Languages : en
Pages : 246
Book Description
Evaporation and Droplet Growth in Gaseous Media
Author: N. A. Fuks
Publisher: Pergamon
ISBN:
Category : Science
Languages : en
Pages : 88
Book Description
Publisher: Pergamon
ISBN:
Category : Science
Languages : en
Pages : 88
Book Description