Konrad Gumowski | Warsaw University of Technology (original) (raw)

Uploads

Papers by Konrad Gumowski

The objective was to study second transition phenomenon and to make transition between second and... more The objective was to study second transition phenomenon and to make transition between second and third regimes better known. We present in this communication very controlled experiments concerning second instabilities in the wake of the sphere. We discuss the first transition from homogenous flow to a stationary instability and we present original results about peristaltic instability preceeding the hairpins shedding.

We perform numerical simulations and also experiments in water channels, on flows behind a solid ... more We perform numerical simulations and also experiments in water channels, on flows behind a solid sphere in order to study the transitional flow, in the range of Reynolds number between 200 and 300, which shows successively stationary axysimmetrical properties, stationary non-axysimmetrical instability and global temporal instability. The numerical study, with spectral methods, shows how the symmetry breaking in the recirculation bubble induces streamwise vortex. In addition we experimentally study the influence of the real conditions of holding of the sphere, on the stationary instability, Finally, we perform very controlled experiments forcing the streamwise vortex, in order to follow the dynamics of formation of the hairpin vortex shedding.

The European Physical Journal E, 2014

We present new experimental results on the development of turbulent spots in channel flow. The in... more We present new experimental results on the development of turbulent spots in channel flow. The internal structure of a turbulent spot is measured, with Time Resolved Stereoscopic Particle Image Velocimetry. We report the observation of travelling-wave-like structures at the trailing edge of the turbulent spot. Special attention is paid to the large-scale flow surrounding the spot. We show that this large-scale flow is an asymmetric quadrupole centred on the spot. We measure the time evolution of the turbulent fluctuations and the mean flow distortions and compare these with the predictions of a nonlinear reduced order model predicting the main features of subcritical transition to turbulence.

The European Physical Journal E, 2014

We present new experimental results on the development of turbulent spots in channel flow. The in... more We present new experimental results on the development of turbulent spots in channel flow. The internal structure of a turbulent spot is measured, with Time Resolved Stereoscopic Particle Image Velocimetry. We report the observation of travelling-wave-like structures at the trailing edge of the turbulent spot. Special attention is paid to the large-scale flow surrounding the spot. We show that this large-scale flow is an asymmetric quadrupole centred on the spot. We measure the time evolution of the turbulent fluctuations and the mean flow distortions and compare these with the predictions of a nonlinear reduced order model predicting the main features of subcritical transition to turbulence.

Surface and Coatings Technology, 2013

ABSTRACT We propose an accessible method of superhydrophobic coating fabrication, in the form of ... more ABSTRACT We propose an accessible method of superhydrophobic coating fabrication, in the form of an epoxy resin composite with hard nano- and microfillers, combined with surface sandblasting and wet chemical hydrophobization. The fillers – glass microbeads and Al2O3 nanoparticles, dispersed in the bulk composite – provide a dual-sized roughness, if exposed on the surface. Sandblasting with corundum particles and subsequent air plasma etching exposes and enhances the micro- and nano-scale roughness, while wet chemical modification with 1H,1H,2H,2H-perfluorodecyltrichlorosilane reduces surface free energy to the level required for superhydrophobic materials. The coatings exhibit superhydrophobic behavior, with water contact angle of 152° and contact angle hysteresis of 8°. Hierarchical surface structure of coatings is preserved after erosive wear tests and superhydrophobicity is restored upon re-hydrophobization.

Journal of Physics: Conference Series, 2014

Flight like droplet impact with superhydrophobic substrate in conditions favour icing is discusse... more Flight like droplet impact with superhydrophobic substrate in conditions favour icing is discussed in this work. Test stand with fast camera and equipment eligible to obtain temperatures and humidity at different ranges, lead to results which can prove, that superhydrophobic surface might be good ice repellent substrate. The influence of air humidity on droplet freezing was confirmed.

Archives of Mechanics

The subject of the present paper is the applicability of hydrophobic surfaces for passive anti-ic... more The subject of the present paper is the applicability of hydrophobic surfaces for passive anti-icing protection. The experiments were focused on freezing droplets and on various droplet impingement and deformation scenarios. Droplet impact was investigated using high-speed camera for surfaces with different physico-chemical properties. To investigate the difference in droplet behavior on the surfaces with different wettability the steel and the aluminum plates were used and compared with specially designed surfaces characterized by a low surface energy. The influence of air humidity on droplet freezing was confirmed. The effective prevention of icing was observed only if humidity was removed from the system during the experiment.

Journal of Physics: Conference Series, 2014

Flight like droplet impact with superhydrophobic substrate in conditions favour icing is discusse... more Flight like droplet impact with superhydrophobic substrate in conditions favour icing is discussed in this work. Test stand with fast camera and equipment eligible to obtain temperatures and humidity at different ranges, lead to results which can prove, that superhydrophobic surface might be good ice repellent substrate. The influence of air humidity on droplet freezing was confirmed.

We performed precise and systematic experiments with PIV in order to measure the velocity field i... more We performed precise and systematic experiments with PIV in order to measure the velocity field in the wake of a solid sphere in a water channel, in the range of Reynolds number between 200 and 400, where stationary and oscillatory instabilities appear, including hairpin shedding regime. From these experimental data, we are studying the modal decomposition of the streamwise vorticity

Surface and Coatings Technology, 2013

ABSTRACT We propose an accessible method of superhydrophobic coating fabrication, in the form of ... more ABSTRACT We propose an accessible method of superhydrophobic coating fabrication, in the form of an epoxy resin composite with hard nano- and microfillers, combined with surface sandblasting and wet chemical hydrophobization. The fillers – glass microbeads and Al2O3 nanoparticles, dispersed in the bulk composite – provide a dual-sized roughness, if exposed on the surface. Sandblasting with corundum particles and subsequent air plasma etching exposes and enhances the micro- and nano-scale roughness, while wet chemical modification with 1H,1H,2H,2H-perfluorodecyltrichlorosilane reduces surface free energy to the level required for superhydrophobic materials. The coatings exhibit superhydrophobic behavior, with water contact angle of 152° and contact angle hysteresis of 8°. Hierarchical surface structure of coatings is preserved after erosive wear tests and superhydrophobicity is restored upon re-hydrophobization.

The objective was to study second transition phenomenon and to make transition between second and... more The objective was to study second transition phenomenon and to make transition between second and third regimes better known. We present in this communication very controlled experiments concerning second instabilities in the wake of the sphere. We discuss the first transition from homogenous flow to a stationary instability and we present original results about peristaltic instability preceeding the hairpins shedding.

We perform numerical simulations and also experiments in water channels, on flows behind a solid ... more We perform numerical simulations and also experiments in water channels, on flows behind a solid sphere in order to study the transitional flow, in the range of Reynolds number between 200 and 300, which shows successively stationary axysimmetrical properties, stationary non-axysimmetrical instability and global temporal instability. The numerical study, with spectral methods, shows how the symmetry breaking in the recirculation bubble induces streamwise vortex. In addition we experimentally study the influence of the real conditions of holding of the sphere, on the stationary instability, Finally, we perform very controlled experiments forcing the streamwise vortex, in order to follow the dynamics of formation of the hairpin vortex shedding.

The European Physical Journal E, 2014

We present new experimental results on the development of turbulent spots in channel flow. The in... more We present new experimental results on the development of turbulent spots in channel flow. The internal structure of a turbulent spot is measured, with Time Resolved Stereoscopic Particle Image Velocimetry. We report the observation of travelling-wave-like structures at the trailing edge of the turbulent spot. Special attention is paid to the large-scale flow surrounding the spot. We show that this large-scale flow is an asymmetric quadrupole centred on the spot. We measure the time evolution of the turbulent fluctuations and the mean flow distortions and compare these with the predictions of a nonlinear reduced order model predicting the main features of subcritical transition to turbulence.

The European Physical Journal E, 2014

We present new experimental results on the development of turbulent spots in channel flow. The in... more We present new experimental results on the development of turbulent spots in channel flow. The internal structure of a turbulent spot is measured, with Time Resolved Stereoscopic Particle Image Velocimetry. We report the observation of travelling-wave-like structures at the trailing edge of the turbulent spot. Special attention is paid to the large-scale flow surrounding the spot. We show that this large-scale flow is an asymmetric quadrupole centred on the spot. We measure the time evolution of the turbulent fluctuations and the mean flow distortions and compare these with the predictions of a nonlinear reduced order model predicting the main features of subcritical transition to turbulence.

Surface and Coatings Technology, 2013

ABSTRACT We propose an accessible method of superhydrophobic coating fabrication, in the form of ... more ABSTRACT We propose an accessible method of superhydrophobic coating fabrication, in the form of an epoxy resin composite with hard nano- and microfillers, combined with surface sandblasting and wet chemical hydrophobization. The fillers – glass microbeads and Al2O3 nanoparticles, dispersed in the bulk composite – provide a dual-sized roughness, if exposed on the surface. Sandblasting with corundum particles and subsequent air plasma etching exposes and enhances the micro- and nano-scale roughness, while wet chemical modification with 1H,1H,2H,2H-perfluorodecyltrichlorosilane reduces surface free energy to the level required for superhydrophobic materials. The coatings exhibit superhydrophobic behavior, with water contact angle of 152° and contact angle hysteresis of 8°. Hierarchical surface structure of coatings is preserved after erosive wear tests and superhydrophobicity is restored upon re-hydrophobization.

Journal of Physics: Conference Series, 2014

Flight like droplet impact with superhydrophobic substrate in conditions favour icing is discusse... more Flight like droplet impact with superhydrophobic substrate in conditions favour icing is discussed in this work. Test stand with fast camera and equipment eligible to obtain temperatures and humidity at different ranges, lead to results which can prove, that superhydrophobic surface might be good ice repellent substrate. The influence of air humidity on droplet freezing was confirmed.

Archives of Mechanics

The subject of the present paper is the applicability of hydrophobic surfaces for passive anti-ic... more The subject of the present paper is the applicability of hydrophobic surfaces for passive anti-icing protection. The experiments were focused on freezing droplets and on various droplet impingement and deformation scenarios. Droplet impact was investigated using high-speed camera for surfaces with different physico-chemical properties. To investigate the difference in droplet behavior on the surfaces with different wettability the steel and the aluminum plates were used and compared with specially designed surfaces characterized by a low surface energy. The influence of air humidity on droplet freezing was confirmed. The effective prevention of icing was observed only if humidity was removed from the system during the experiment.

Journal of Physics: Conference Series, 2014

Flight like droplet impact with superhydrophobic substrate in conditions favour icing is discusse... more Flight like droplet impact with superhydrophobic substrate in conditions favour icing is discussed in this work. Test stand with fast camera and equipment eligible to obtain temperatures and humidity at different ranges, lead to results which can prove, that superhydrophobic surface might be good ice repellent substrate. The influence of air humidity on droplet freezing was confirmed.

We performed precise and systematic experiments with PIV in order to measure the velocity field i... more We performed precise and systematic experiments with PIV in order to measure the velocity field in the wake of a solid sphere in a water channel, in the range of Reynolds number between 200 and 400, where stationary and oscillatory instabilities appear, including hairpin shedding regime. From these experimental data, we are studying the modal decomposition of the streamwise vorticity

Surface and Coatings Technology, 2013

ABSTRACT We propose an accessible method of superhydrophobic coating fabrication, in the form of ... more ABSTRACT We propose an accessible method of superhydrophobic coating fabrication, in the form of an epoxy resin composite with hard nano- and microfillers, combined with surface sandblasting and wet chemical hydrophobization. The fillers – glass microbeads and Al2O3 nanoparticles, dispersed in the bulk composite – provide a dual-sized roughness, if exposed on the surface. Sandblasting with corundum particles and subsequent air plasma etching exposes and enhances the micro- and nano-scale roughness, while wet chemical modification with 1H,1H,2H,2H-perfluorodecyltrichlorosilane reduces surface free energy to the level required for superhydrophobic materials. The coatings exhibit superhydrophobic behavior, with water contact angle of 152° and contact angle hysteresis of 8°. Hierarchical surface structure of coatings is preserved after erosive wear tests and superhydrophobicity is restored upon re-hydrophobization.