The Experts below are selected from a list of 3102 Experts worldwide ranked by ideXlab platform
Philippe Lavoie - One of the best experts on this subject based on the ideXlab platform.
-
spatiotemporal analysis of fluctuating base pressure and velocity in a blunt trailing edge wake
54th AIAA Aerospace Sciences Meeting, 2016Co-Authors: Heather A. Clark, Philippe LavoieAbstract:Three-dimensional instabilities in the wake of a blunt trailing edge profiled body are examined through experimental measurements of velocity and the Spanwise Distribution of fluctuating surface pressure on the model rear face near separation. Spatial and temporal variability of the vortex shedding behaviour result in low-frequency modulation of the pressure signals. The time-dependent amplitude is characterized using the wavelet transform, while subsequent correlation analysis and reduced-order modelling provide quantitative evidence of the dominant influence of large-scale instabilities. The cross-correlation of the wake velocity and the surface pressure are examined in the framework of the Extended Proper Orthogonal Decomposition, through which reduced-order models of the measured variables are related to construct an empirical estimator of velocity. Implications of the observed modal correlations and the statistical signature of large-scale spatial variations are discussed in relation to the estimation of multi-scale wake phenomena.
Clara Velte - One of the best experts on this subject based on the ideXlab platform.
-
validation of a model for estimating the strength of the vortex created by a vortex generator from its bound circulation
arXiv: Fluid Dynamics, 2019Co-Authors: Martin Otto Laver Hansen, Antonis Charalampous, Jean-marc Foucaut, Christophe Cuvier, Clara VelteAbstract:A hypothesis is tested and validated for predicting the vortex strength induced by a vortex generator in wall-bounded flow by combining the knowledge of the Vortex Generator (VG) geometry and the approaching boundary layer velocity Distribution. In this paper, the Spanwise Distribution of bound circulation on the vortex generator is computed from integrating the pressure force along the VG height calculated using CFD. It is then assumed that all this bound circulation is shed into the wake to fulfill Helmholtz's theorem and then curl up into one primary tip vortex. To validate this, the trailed circulation estimated from the Distribution of the bound circulation is compared to the one in the wake behind the vortex generator determined directly from the wake velocities at some downstream distance. In practical situations, the pressure Distribution on the vane is unknown and consequently other estimates of the Spanwise force Distribution on the VG must instead be applied, such as using 2D airfoil data corresponding to the VG geometry at each wall-normal distance. Such models have previously been proposed and used as an engineering tool to aid preliminary VG design and it is not the purpose of this paper to refine such engineering models, but to validate their assumptions such as applying a lifting line model on a VG that has a very low aspect ratio and placed in wall boundary layer. Herein, high Reynolds number boundary layer measurements of VG induced flow were used to validate the Reynolds Averaged Navier-Stokes (RANS) modeled circulation results and are used for further illustration and validation of the hypothesis.
-
Validation of a Model for Estimating the Strength of a Vortex Created from the Bound Circulation of a Vortex Generator
Energies, 2019Co-Authors: Martin Hansen, Antonis Charalampous, Jean-marc Foucaut, Christophe Cuvier, Clara VelteAbstract:A hypothesis was tested and validated for predicting the vortex strength induced by a vortex generator in wall-bounded flow by combining the knowledge of the Vortex Generator (VG) geometry and the approaching boundary layer velocity Distribution. In this paper, the Spanwise Distribution of bound circulation on a vortex generator was computed by integrating the pressure force along the VG height, calculated using Computational Fluid Dynamics (CFD). It was then assumed that all this bound circulation was shed into a wake to fulfill Helmholtz's theorem which then curls up into one primary tip vortex. To validate this, the trailed circulation estimated from the Distribution of the bound circulation was compared to the one in the wake behind the vortex generator, determined directly from the wake velocities at some downstream distance. In practical situations, the pressure Distribution on a vane is unknown and consequently other estimates of the Spanwise force Distribution on a VG must instead be applied, such as using 2D airfoil data corresponding to the VG geometry at each wall-normal distance. Such models have previously been proposed and used as an engineering tool to aid preliminary VG design. Therefore, it is not the purpose of this paper to refine such engineering models, but rather to validate their assumptions, such as applying a lifting line model on a VG that has a very low aspect ratio and is placed in a wall boundary layer. Herein, high Reynolds number boundary layer measurements of VG-induced flow were used to validate the Reynolds-Averaged Navier-Stokes (RANS) model circulation results, which were used for further illustration and validation of the hypothesis.
Heather A. Clark - One of the best experts on this subject based on the ideXlab platform.
-
spatiotemporal analysis of fluctuating base pressure and velocity in a blunt trailing edge wake
54th AIAA Aerospace Sciences Meeting, 2016Co-Authors: Heather A. Clark, Philippe LavoieAbstract:Three-dimensional instabilities in the wake of a blunt trailing edge profiled body are examined through experimental measurements of velocity and the Spanwise Distribution of fluctuating surface pressure on the model rear face near separation. Spatial and temporal variability of the vortex shedding behaviour result in low-frequency modulation of the pressure signals. The time-dependent amplitude is characterized using the wavelet transform, while subsequent correlation analysis and reduced-order modelling provide quantitative evidence of the dominant influence of large-scale instabilities. The cross-correlation of the wake velocity and the surface pressure are examined in the framework of the Extended Proper Orthogonal Decomposition, through which reduced-order models of the measured variables are related to construct an empirical estimator of velocity. Implications of the observed modal correlations and the statistical signature of large-scale spatial variations are discussed in relation to the estimation of multi-scale wake phenomena.
Michael J Gollner - One of the best experts on this subject based on the ideXlab platform.
-
an investigation of coherent structures in laminar boundary layer flames
Combustion and Flame, 2017Co-Authors: Colin Miller, Wei Tang, Mark A Finney, Sara Mcallister, Jason Forthofer, Michael J GollnerAbstract:Abstract Observations of coherent structures in boundary layer flames, particularly wildland fires, motivated an investigation on instabilities in a boundary layer flame. This experimental study examined streaklike structures in a stationary diffusion flame stabilized within a laminar boundary layer. The incoming flow was characterized with a hotwire anemometer, and locations of the flame streaks were found to align with pre-existing velocity perturbations. These upstream disturbances enabled stabilization of flame streaks, which could then be probed with point measurements. Flame streaks were seen to amplify with the streamwise development of the fire, and this growth was quantified via thermocouple measurements. Temperature mapping of the flame streaks indicated a temperature rise in the flame streaks, while the region in between these streaks, the trough, was seen to decrease in temperature. The heat flux to the surface was measured with a total heat flux gauge. Measurements were taken below the flame streaks and below the regions between the streaks (i.e., troughs). At all measurement locations, the heat flux below the troughs was found to be higher. This was likely a function of the flame standoff distance, and indicated that the flame streaks were acting to modify the Spanwise Distribution of heat flux. The presence of instabilities had a significant effect on the Spanwise Distribution of heat transfer. Instantaneous properties in boundary layer combustion can vary significantly due to three-dimensional effects, and this may have significant implications for describing and modeling boundary layer combustion.
Colin Miller - One of the best experts on this subject based on the ideXlab platform.
-
an investigation of coherent structures in laminar boundary layer flames
Combustion and Flame, 2017Co-Authors: Colin Miller, Wei Tang, Mark A Finney, Sara Mcallister, Jason Forthofer, Michael J GollnerAbstract:Abstract Observations of coherent structures in boundary layer flames, particularly wildland fires, motivated an investigation on instabilities in a boundary layer flame. This experimental study examined streaklike structures in a stationary diffusion flame stabilized within a laminar boundary layer. The incoming flow was characterized with a hotwire anemometer, and locations of the flame streaks were found to align with pre-existing velocity perturbations. These upstream disturbances enabled stabilization of flame streaks, which could then be probed with point measurements. Flame streaks were seen to amplify with the streamwise development of the fire, and this growth was quantified via thermocouple measurements. Temperature mapping of the flame streaks indicated a temperature rise in the flame streaks, while the region in between these streaks, the trough, was seen to decrease in temperature. The heat flux to the surface was measured with a total heat flux gauge. Measurements were taken below the flame streaks and below the regions between the streaks (i.e., troughs). At all measurement locations, the heat flux below the troughs was found to be higher. This was likely a function of the flame standoff distance, and indicated that the flame streaks were acting to modify the Spanwise Distribution of heat flux. The presence of instabilities had a significant effect on the Spanwise Distribution of heat transfer. Instantaneous properties in boundary layer combustion can vary significantly due to three-dimensional effects, and this may have significant implications for describing and modeling boundary layer combustion.