Experimental study of simultaneous measurement of velocity and surface topography: in the wake of a circular cylinder at low Reynolds number (original) (raw)
Related papers
Journal of Fluids and Structures, 2008
A technique capable of simultaneous measurement of free surface topography and velocity vector field data is developed. This technique offers substantial benefits of both reduced complexity and enhanced accuracy over all other techniques known to offer the same measurements. The flow behind a circular cylinder at low Reynolds numbers is measured using this technique. The velocity and vorticity fields as well as Strouhal number closely match the expected results. The free surface topography, which can be related to the pressure field, exhibits an intimate relationship to the vorticity field.
Measurement of instantaneous velocity and surface topography
A technique capable of simultaneous measurement of free surface topography and velocity vector field data is developed. This technique offers substantial benefits of both reduced complexity and enhanced accuracy over all other techniques known to offer the same measurements. The flow behind a circular cylinder at low Reynolds numbers is measured using this technique. The velocity and vorticity fields as well as Strouhal number closely match the expected results. The free surface topography, which can be related to the pressure field, exhibits an intimate relationship to the vorticity field.
Measurement of Instantaneous Velocity and Surface Topogra-phy of a Cylinder at Low Reynolds Number
A technique capable of simultaneous measurement of free surface topography and velocity vector field data is developed. This technique offers substantial benefits of both reduced complexity and enhanced accuracy over all other techniques known to offer the same measurements. The flow behind a circular cylinder at low Reynolds numbers is measured using this technique. The velocity and vorticity fields as well as Strouhal number closely match the expected results. The free surface topography, which can be related to the pressure field, exhibits an intimate relationship to the vorticity field.
Experimental Investigation of wake survey over a cylinder with different surface profiles
Laminar air flow over a surface results in turbulent flow at higher Reynolds number due to flow separation. An attempt to delay Flow separation by using different surface profiles has been made. The paper involves experimental investigation of drag on circular cylinder by implementation of smooth, rough and channeled surfaces at three different velocities. The investigation has been carried out in a subsonic wind tunnel to determine how different cylinder surface profiles vary the drag in the wake region of a circular cylinder. The coefficient of pressure and drag has been calculated from the values measured from the wake probe for three different surface profiles at speeds 30, 35 and 40m/s respectively. Graphs has been plotted to show the variation of coefficient of drag along the wake region. This study will help us to correlate and select an appropriate surface profile which delays the separation point and also has a less drag. The results will have a direct application on all circular cylindrical structures such as fuselage, landing gears and towers. It has been found in the study that the channeled surface cylinders has less drag and wakes compared to the smooth and rough surface profiles.
Experimental Thermal and Fluid Science, 1996
HA cross-correlation particle image velocimetry (PIV) technique has been developed to measure the spatiotemporal in-plane velocity vector field evolution of time-dependent flows. A novel iterative two-stage crosscorrelation scheme of two sequential images of flow tracers has been incorporated in the image analysis. The implementation in hardware and software of this complete recording and analysis system are described. The expected accuracy of the velocity measurements was investigated and is discussed. The technique has been applied to study the near wake behind a circular cylinder at low Reynolds numbers (Red). The measurements presented pertain to cylinders with d = 12.5 and 25 mm (l/d = 19.5 and 9.8, respectively). The respective Reynolds numbers Re d are 875 and 769. Two planes of this flow are considered in this study: (1) plane normal to the cylinder axis (xy plane) and (2) a plane containing the cylinder axis and the stream direction (xz plane). Instantaneous in-plane velocity vector fields and out-of-plane vorticity fields are presented for both planes. The effect of spatial resolution on peak vorticity is discussed using velocity vector field measurements in the near wake of the cylinder that were conducted using different spatial resolutions. The three-dimensional nature of the near wake of circular cylinders at low Re d is demonstrated using quantitative in-plane velocity vector field and out-of-plane vorticity measurements. An upstream influx of relatively high velocity fluid into the stagnant near-wake region in the xy plane and the subsequent deflection of the fluid normal to this plane as it approaches the stagnation region at the cylinder are shown to be responsible for the generation of three-dimensional flow in the near wake of a circular cylinder.
Flow structure around geometries similar to circular cylindrical geometries in various industrial and daily life applications must be known in respect of energy efficiency and stability for different flow conditions. In this sense, flow structures in the wake of a circular cylinder located in a boundary layer flow and a flow region near to free flow surface were examined by means of PIV system in an open water channel. Circular cylinder was parallel to boundary layer plate and perpendicular to flow direction. Experiments were conducted primarily in a region near to the free surface of the flow and then in the boundary layer flow at various locations of the cylinder diameter (D) ratios of contacting case, 0.00D, 0.25D, 0.50D and 1.0D. Cylinder diameter was 50 mm and Reynolds number calculated according to this diameter was selected 5000. For the experiments, Stereo Particle Image Velocimetry Setup in Selcuk University Mechanical Engineering Department Hydraulic Laboratory was utilized. Results obtained as the consequence of investigation of flow around circular cylinder at different flow conditions are presented in the form of time averaged streamwise velocity component contours and timeaveraged vorticity contours. It is shown that wake structures of circular cylinder immersed in a boundary layer flow exhibited considerably different characteristics compared to the flow structures obtained at flow region near to free surface of the flow.
Quantitative measurements of three-dim ensional structures in the wake of a circular cylinder
Journal of Fluid Mechanics, 1994
The fine scale three-dimensional structures usually associated with streamwise vortices in the near wake of a circular cylinder have been studied at Reynolds numbers ranging from 170 to 2200. Spatially continuous velocity measurements along lines parallel to the cylinder axis were obtained with a scanning laser anemometer. To detect the streamwise vortices in the amplitude modulated velocity field, it was necessary to develop a spatial decomposition technique to split the total flow into a primary flow component and a secondary flow component. The primary flow is comprised of the mean flow and Strouhal vortices, while the secondary flow is the result of the three-dimensional streamwise vortices that are the essence of transition to turbulence. The three-dimensional flow amplitude increases in the primary vortex formation region, then saturates shortly after the maximum amplitude in the primary flow is reached. In the near-wake region the wavelength decreases approximately like Re−0....
Ship wake study using imaging technique
Geoinformation Science …, 2010
Stimulated by the importance of reducing pollution caused by ship wakes, this study is conducted to design a better hull model that can produce less wave resistance. It is very crucial to measure the ship wake produced during the design stage. The system ...
Experimental Investigation of 3D Dynamical Effects in a Wake behind Circular Cylinder
MATEC Web of Conferences
A circular cylinder in crossflow is subjected to the study of 3D dynamical structure of its wake. The typical dynamics is characterized by quasi-periodic behaviour called Kármán – Bénard vortex street with the typical frequency in dimensionless form known as Strouhal number. The experimental study relies on stereo Particle Image Velocimetry method, the plane of measurement is perpendicular to the flow in the distance 3.8 cylinder diameters in streamwise direction. Reynolds number was around 5 thousand. The structure and dynamical behaviour of the wake along the cylinder axis is studied in details. On the top of the known streamwise velocity deficit definition of the wake, the streamwise oriented dynamically evolving vortices are detected. For the detailed dynamics examination, the Oscillation Pattern Decomposition method was used. Waves of various structures travelling along the cylinder axis as well as some pulsations were identified. The wake dynamics is characterised by the strea...