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(1 - 6 of 6)
- Title
- Numerical Assessment of Eddy-Viscosity Turbulence Models of an Axial-Flow Turbine at a Low Reynolds Number.
- Creator
- Estrada, Nick Dagoberto, Moslemian, Davood, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The flow field behavior of axial flow turbines is of great importance, especially in modern designs that may operate at a low Reynolds number. At these low Reynolds numbers, the efficiency loss is significantly augmented compared to higher Reynolds number flows. A detailed incompressible numerical study of a single stage axial-flow turbine at a low Reynolds number is investigated with the use of multiple eddy-viscosity turbulence models. The study includes epistemic uncertainty quantification...
Show moreThe flow field behavior of axial flow turbines is of great importance, especially in modern designs that may operate at a low Reynolds number. At these low Reynolds numbers, the efficiency loss is significantly augmented compared to higher Reynolds number flows. A detailed incompressible numerical study of a single stage axial-flow turbine at a low Reynolds number is investigated with the use of multiple eddy-viscosity turbulence models. The study includes epistemic uncertainty quantification as a form of numerical error estimation. The numerical results show good qualitative and quantitative agreement with experimental data. It was found that the shear stress transport (SST) k - ω turbulence model with rotation/curvature correction and inclusion of transition modeling is most capable at predicting the mean velocity distribution, which is further enhanced when the URANS formulation is employed. However, all the cases indicate a large variation in the prediction of the root-mean-squared of the turbulent velocity fluctuations.
Show less - Date Issued
- 2016
- PURL
- http://purl.flvc.org/fau/fd/FA00004587, http://purl.flvc.org/fau/fd/FA00004587
- Subject Headings
- Turbomachines--Fluid dynamics., Turbulence--Mathematical models., Structural dynamics., Viscous flow--Mathematical models., Reynolds number., Axial flow.
- Format
- Document (PDF)
- Title
- Numerical Simulation of a Flowfield Around a Hypersonic Missile with Lateral Jets.
- Creator
- Rodriguez, Daniel, Moslemian, Davood, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
This work uses computational fluid dynamics to study the flowfield around a hypersonic missile with two lateral jets to provide control in place of control surfaces. The jets exhaust an H2-O2 mixture at Mach number of 2.9 with a jet pressure ratio of roughly 10,500. The jets are staggered axially and circumferentially in such a way to produce pitch and yaw. The flowfield of such a jet configuration is characterized at several angles of attack and the corresponding force coefficients and...
Show moreThis work uses computational fluid dynamics to study the flowfield around a hypersonic missile with two lateral jets to provide control in place of control surfaces. The jets exhaust an H2-O2 mixture at Mach number of 2.9 with a jet pressure ratio of roughly 10,500. The jets are staggered axially and circumferentially in such a way to produce pitch and yaw. The flowfield of such a jet configuration is characterized at several angles of attack and the corresponding force coefficients and amplification factors are provided. The freestream air and H2-O2 plume is treated as inert for the majority of the calculations. Special cases are treated with finite rate chemical kinetics and compared to the inert flowfield to ascertain the effects that chemical reactions have on the force coefficients. It was found that the flowfield was only slightly altered from the familiar one jet flowfield when the second jet is active. The flow topology and vortex structures tend to shift towards the second jet but the overall structure remains the same. The normal force amplification factors are close to unity over the range of angle of attack due to the thrust being so high with the two jet configuration having a lower amplification factor compared to firing a single jet. Treating the flowfield as chemically reacting did not affect the force values much: the difference being 0.3% for an angle of attack of 0°.
Show less - Date Issued
- 2017
- PURL
- http://purl.flvc.org/fau/fd/FA00004893, http://purl.flvc.org/fau/fd/FA00004893
- Subject Headings
- Aerodynamics, Hypersonic., Nonequilibrium thermodynamics., Aerothermodynamics--Mathematica., Hypersonic planes--Design and construction--Mathematical models., Vortex-motion--Mathematical models.
- Format
- Document (PDF)
- Title
- Design and evaluation of a swirling flow combustion system.
- Creator
- Li, Ceji., Florida Atlantic University, Moslemian, Davood, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A swirling flow combustion system has been designed and constructed. An integral laser Doppler velocimeter is constructed for the investigations of fluid mechanics aspects of a swirling flow combustor. The combustor consists of one fuel flow and two swirled air flows. The inner air flow has a fixed swirling strength and the outer air flow has an adjustable swirler. Both counterswirl and coswirl flows with variable swirl strength can be generated. Premixed or non-premixed combustion can be...
Show moreA swirling flow combustion system has been designed and constructed. An integral laser Doppler velocimeter is constructed for the investigations of fluid mechanics aspects of a swirling flow combustor. The combustor consists of one fuel flow and two swirled air flows. The inner air flow has a fixed swirling strength and the outer air flow has an adjustable swirler. Both counterswirl and coswirl flows with variable swirl strength can be generated. Premixed or non-premixed combustion can be investigated on this system. Evaluation of the swirling combustion system and performance check of the velocity measurement system are conducted. Detailed time mean and fluctuating flow measurements are obtained for coswirl and counterswirl conditions with the LDV system. A central recirculation zone is observed in both swirl conditions, but the size in counterswirl is much smaller. The reasons for the difference are discussed.
Show less - Date Issued
- 1991
- PURL
- http://purl.flvc.org/fcla/dt/14767
- Subject Headings
- Fluid dynamics, Vortex-motion, Combustion chambers
- Format
- Document (PDF)
- Title
- Pressure fluctuations within a large particle gas fluidized bed in the presence of horizontal tube banks.
- Creator
- Ni, Li., Florida Atlantic University, Moslemian, Davood, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A bench-scale fluidized bed has been designed and constructed for the investigation of pressure fluctuations within a large particle gas fluidized bed in the presence of horizontal tube banks. The pressure fluctuations inside the fluidized bed are investigated under different operating conditions, including a range of fluidization velocities, two particle sizes and two configurations of the tube banks. Different flow parameters like the standard deviation of the pressure fluctuations, 90%...
Show moreA bench-scale fluidized bed has been designed and constructed for the investigation of pressure fluctuations within a large particle gas fluidized bed in the presence of horizontal tube banks. The pressure fluctuations inside the fluidized bed are investigated under different operating conditions, including a range of fluidization velocities, two particle sizes and two configurations of the tube banks. Different flow parameters like the standard deviation of the pressure fluctuations, 90% fluctuation ranges, power spectral density functions, dominant fluctuation frequencies, autocorrelation and crosscorrelation coefficients, and Hurst exponents by fractal analysis are determined. From the experimental data, quantitative information on the fluctuations are generated for use in evaluating the dynamic behavior of the fluidized bed. These parameters are found to strongly depend on fluidization velocity, configurations of tube banks and position in the bed. The flow regime characteristics with different flow parameters are discussed according to these results.
Show less - Date Issued
- 1993
- PURL
- http://purl.flvc.org/fcla/dt/14885
- Subject Headings
- Fluidization, Fluidized bed combustion
- Format
- Document (PDF)
- Title
- Viscosity correction for breathing gas mixtures measured via a laminar flow element.
- Creator
- Signo, Barbara., Florida Atlantic University, Moslemian, Davood, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
To minimize previously observed inaccuracies in the measurement of the flow rates of breathing gas mixtures, errors in the measurement of the pressure differential across the LFE with short diffusers using high frequency response pressure transducers were ruled out. A Laminar Flow Element was calibrated with air, nitrogen, and helium at various pressure and temperature conditions. The feasibility of using the Universal Calibration Curve determined from atmospheric air data to estimate the...
Show moreTo minimize previously observed inaccuracies in the measurement of the flow rates of breathing gas mixtures, errors in the measurement of the pressure differential across the LFE with short diffusers using high frequency response pressure transducers were ruled out. A Laminar Flow Element was calibrated with air, nitrogen, and helium at various pressure and temperature conditions. The feasibility of using the Universal Calibration Curve determined from atmospheric air data to estimate the flow rate of other gases at hyperbaric conditions was evaluated. The viscosity values of pure gases calculated by theoretical methods were compared to the viscosity values estimated by using the Universal Calibration Curve Viscosity Iteration method. Using flowrate calibration data for the gas mixtures of interest, the viscosity values for these gas mixtures were estimated. These viscosity values were then compared to the corresponding viscosity values calculated by theoretical methods. The Universal Calibration Curve obtained by fitting flowrate calibration data of air flowing at STP can be used to estimate the flow of other gases flowing at hyperbaric pressures.
Show less - Date Issued
- 1993
- PURL
- http://purl.flvc.org/fcla/dt/14981
- Subject Headings
- Viscosity, Gases--Viscosity, Flow meters, Gas flow--Measurement
- Format
- Document (PDF)
- Title
- Computed tomographic measurements of void fraction and modeling of the flow in bubble columns.
- Creator
- Kumar, Sailesh B., Florida Atlantic University, Moslemian, Davood, Dudukovic, M. P., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A complete understanding of the gas-liquid two phase flow in bubble columns is required for the development of reliable models for scale-up of these multiphase reactors. Although several models have been proposed to describe the hydrodynamics. lack of adequate experimental data has hindered meaningful evaluation of model parameters and model predictions. The Computer Automated Radioactive Particle Tracking ( CARPT) facility that was implemented earlier has provided interesting results on the...
Show moreA complete understanding of the gas-liquid two phase flow in bubble columns is required for the development of reliable models for scale-up of these multiphase reactors. Although several models have been proposed to describe the hydrodynamics. lack of adequate experimental data has hindered meaningful evaluation of model parameters and model predictions. The Computer Automated Radioactive Particle Tracking ( CARPT) facility that was implemented earlier has provided interesting results on the recirculation patterns of the liquid phase. The technique has provided quantitative information on liquid velocities and turbulence parameters as well. In addition to these hydrodynamic parameters the measurement of void fraction is also important. To complement the capabilities of CARPT a scanner for ;-ray Computed Tomography (CT) was implemented to quantify the local void fraction and its distribution in two phase flow systems. The automated scanner is capable of imaging flows in test sections between 0.02.5 m and 0..15 m in diameter at different elevations above the distributor. The scanner makes use of the same detectors used in the CARPT facility and with the use of a specially designed moving collimator provides a spatial resolution of about 5 mm. A non-conventional algorithm based on maximum likelihood principles called the E-M algorithm was used for imagw reconstruction. Long scanning times are required leading to time averaged density profiles. Although the system is only capable of providing time averaged void fraction distributions. it can provide unique information concerning the structure of two phase flow. The system performance was evaluated by identifying the sources of errors in measurement and their bounds. The capabilities of the scanner for imaging void fraction distribution was demonstrated both qualitatively and quantitatively. Fse of existing radiation detectors and the associated signal processing and data acquisition system helped in reducing the cost of the system. The scanner was utilized to quantify the local void fraction and its distribution in bubble columns of five diameters (0.10. 0.14, 0.19, 0.26. 0.30 m internal diameter) and at four superficial gas velocities. The effect of various operating parameters such as column diameter, superficial gas velocity. the type of distributor. the static liquid height and some changes in the physical properties of the liquid phase were studied. For the first time a comprehensive characterization of the void fraction in an air water bubble column using a non-invasive technique was achieved. The experimental data obtained using CARPT and CT under identical operating conditions was used for developing a methodology for scale-up of bubble columns using a one dimensional model for liquid recirculation. Successful scale-up of liquid hydrodynamics using a one dimensional model requires an adequate closure scheme for the Reynolds shear stress. The existing correlations for the prescription of the eddy viscosity or the mixing length scale are demonstrated to be applicable only for a limited range of conditions. and consequently cannot be used for scale-up predictions. A method for estimating the mixing length scale has been explored and an attempt at unifying a wide range of data available in the literature within the pun·iew of the method has been made. The futility of such an attempt is attributed to the non-reproducibility of the flow in different laboratories and the conasequent lack of data obtained under identical conditions. It is demonstrated, however, that scale-up based on the mixing length distribution is possible when it is obtained from a consistent set of data for liquid velocity and gas void fraction profiles. Using the present method for prescribing the mixing length scale. model predictions for scale-up compare satisfactorily for the data that was obtained as part of this research. The achievement was that the turbulence length scale estimated in one column diameter was successfully used in predicting the liquid velocities in larger diameter columns.
Show less - Date Issued
- 1994
- PURL
- http://purl.flvc.org/fcla/dt/12384
- Subject Headings
- Two-phase flow, Hydrodynamics, Bubble chambers, Tomography, Emission
- Format
- Document (PDF)
