Surface Flow Visualization Technique Research Articles

Orifice Jet Curvature and Its Interaction With a Row of Short Pin-Fins

Abstract The fluidic behaviors and interactions present in a setup utilizing perforated blockages and downstream pin-fin are elucidated: specifically, the role of jet curvature in flow interactions and the interaction of end-wall flows around the pin-fins subjected to impinging jet. To this end, a combination of particle image velocimetry-based measurements and oil-dye surface flow visualization technique is utilized. Two different configurations of jet flows, with or without flanking jets, and three different distances between the pin-fins and blockages were considered. Jet curvature can result in flow inclinations of as much as 45 deg–60 deg interacting with the pin-fins and the majority of the jet flow is skewed toward the inner side of the pin-fin. At the end-wall, the interaction with nearby structures, being blockages or pin-fins, alters the shape and profile of the flows. This alteration is in contrast to those around conventional pin-fin arrays which remain largely unaltered in the presence of nearby pin-fins.

Experimental and numerical modeling of an air jet impingement system

One of the challenges of air jet impingement systems is the interaction between jets in the case of impingement with nozzle arrays. This study is focused on the wall shear stress exerted by the fluid, as it is closely related to surface heat transfer. The strengths and weaknesses of the different turbulence models for a specific case are highlighted. To examine this effect, a qualitative comparative analysis between a physical model and a computational model is designed. The computational model is evaluated with five different turbulence modeling techniques to determine which one of these predicts this effect better. The surface flow visualization technique has been used to determine the wall shear stress experimentally. The tested case is formed by a 9 nozzle square regular array at a Reynolds number of 8500 with the air outlet in minimum crossflow configuration. The traces left by the fluid and the particle density can be qualitatively related to the wall shear stress and compared with the scalar fields of the simulations. Up to four regions of interest in three nozzle positions have been studied. The results show better performance of the LES technique predicting the stagnation point location, as well as cross-fountain region shape and size. Through this work, the suitability of the techniques to the surface observations can be determined.

STUDY ON INSTANTANEOUS-ADVECTIVE STRUCTURES OF LARGE SCALE COHERENT VORTICES GENERATED DOWNSTREAM OF A SINGLE GROYNE

To investigate the instantaneous flow patterns around a single groyne, a scale model was installed in the shallow water channel and experiments were conducted by means of surface flow visualization technique. A particle tracking velocimetry (PTV) method has been developed for shallow flow conditions and has been adopted to estimate the instantaneous velocity fields to cope with the problem of a very high dynamic velocity range behind the groyne. Proper orthogonal decomposition (POD) is applied to obtain an effect of the fluctuating flow pattern and its coherent structures. Conditional sampling technique (CST) is also applied to reveal the advection properties of POD decomposed flow pattern. POD decomposed coherent patterns and their advection properties under submerged and emerged conditions. One of main results is the distribution of coherent vortices generated at the groyne tip due to high shear forces in the mixing layer between main stream and dead zone.

STUDY ON SHALLOW FLOW VISUALIZATION AROUND SINGLE GROYNE AND THE MEAN/COHERENT FLOW STRUCTURES

Groynes have been used for the stabilization of banks and for creating a navigation channel by confining the cross-sectional area, especially for large European and Japanese rivers. Therefore, turbulent flows and transport phenomena in groyne fields have paid attention to the appropriate design for bank protection and obtainment of enough depth in the main channel as well as the proper environment for ecosystems. In the present study, mean and coherent flow structures around single groyne under emerged and submerged conditions were experimentally discussed. In order to investigate the flow pattern around the single groyne, a scaled and schematized model was implemented and experiments were conducted by means of surface flow visualization technique and Particle Tracking Velocimetry (PTV). Furthermore, analytical techniques of proper orthogonal decomposition (POD) are applied to reveal typical pattern of coherent structures.

Measurement of shear-stress distribution over a surface by liquid-crystalcoating

In this paper, a method for measuring the instantaneous shear-stress distributionover a solid surface in a fluid flow is studied by using a surface-flow visualizationtechnique with a shear-sensitive liquid-crystal coating. The colour response of theliquid-crystal coating is calibrated against the various shear-stress magnitudes anddirections with an experimental test section of laminar channel flow. Themeasurement of instantaneous shear-stress distribution is carried out usingtwo colour CCD cameras, which are situated side by side in stereoscopicarrangement. The colour-to-shear-stress transformation is conducted by analysingthe hue distribution of the visualized colour image with the calibratedrelationships between the hues from the two colour CCD cameras and theshear-stress magnitude and direction. The usefulness of this technique wasdemonstrated by the measurement of shear-stress distribution arounda circular cylinder on a surface under decelerating flow conditions.

B310 液晶を用いたせん断応力分布の瞬時計測法と非定常流への応用

A method for measuring the instantaneous shearstress distribution over a solid surface in a fluid flow is studied by using a surface-flow visualization technique with a shear-sensitive liquid-crystal coating. The color response of the liquid-crystal coating is calibrated against the various shearstress magnitudes and directions with an experimental test section of laminar channel flow. The measurement of instantaneous shear-stress distribution is carried out by using two color CCD cameras, which are situated side by side in stereoscopic arrangement. The color to shear stress transformation is conducted by analyzing the hue distribution of the visualized color image with the calibrated relationships between the hues from the two colour CCD cameras and the shearstress magnitude and direction. The usefulness of this technique was demonstrated by the measurement of shear-stress distribution around a circular cylinder over a surface under the decelerating flow condition.

B132 対称翼から発生する離散周波数騒音の円柱後流による低減機構

The discrete frequency noise is generated from an airfoil in a uniform flow at small angle of attack to the free stream at moderate Reynolds number. The present experiment is conducted to find the reduction condition of discrete frequency noise by the influence of cylinder wake using a surface-flow visualization technique by shear-stress sensitive liquid crystal coating. Utilizing the color image analysis, the point of flow separation and reattachment is evaluated from the visualized images. It is found that the region of flow separation over the airfoil was fairly reduced by the influence of cylinder wake, where the suppression of discrete frequency noise was observed. The laminar boundary-layers over the airfoil seems to be shifted to a turbulent state by the influence of cylinder wake.

The 9th Millennium International Symposium on FlowVisualization

The 9th Millennium International Symposium on Flow Visualization (9misfv) was held in Edinburgh, Scotland from the 22nd August to the 25th August 2000. The symposium attracted, by a significant amount, the largest number of participants in the history of the symposium series. A total of 396 presentations were made at the symposium. These were distributed through 74 technical sessions covering a full spectrum of topics in 373 oral presentations and 23 poster presentations. The symposium commenced with an opening address and welcome to delegates by the Symposium Chairman, Professor I. Grant. The technical presentations commenced with Professor G. M. Carlomagno giving the invited Leonardo da Vinci Memorial Lecture entitled "Infrared Thermography: a Particular Surface Flow Visualization Technique." Each day of the meeting commenced with an invited Keynote lecture, given in plenary session, by a recognised authority in the respective area. These were, in order of presentation, Professor Toshio Kobayashi "High Performance Computation and Visualization of Fluid Flows," Dr. Juergen Kompenhans "Qualitative and Quantitative Visualization of Wake Vortices in Industrial Test Facilities," Professor Jim Whitelaw "Aspects of Unsteady Combustion" and Professor Mory Gharib "On the Role of Flow Visualization in the Understanding of Cardiovascular Fluid Dynamics: from da Vinci to Harvey." During the symposium two awards were made to distinguished scientists. These were the Leonardo da Vinci award to Professor Giovanni Carlomagno and the Asanuma award to Professor Wolfgang Merzkirch.

Surface flow visualization using the thermal wakes of small heated spots

This note describes a surface flow visualization technique which uses the thermal wakes of an array of small heated spots to infer the local flow direction. The thermal wake is made visible using wide band thermochromic liquid crystals. The technique is illustrated using the endwall flow under a horseshoe vortex at the base of a right circular cylinder in a turbulent boundary layer. Comparisons to results generated using the oil of wintergreen technique were in good agreement. In addition to surface flow direction, the technique has the potential to be used to measure the heat transfer coefficient at each spot. Data are presented in terms of photographs of the actual visualization surface. The techniques is suitable for low speed flows.

The Aerodynamic Mixing Effect of Discrete Cooling Jets With Mainstream Flow on a Highly Loaded Turbine Blade

For the application of film cooling to turbine blades, experimental investigations were performed on the mixing processes in the near-hole region with a row of holes on the suction suction side of a turbine cascade. Data were obtained using pneumatic probes, pressure tappings, and a three-dimensional subminiature hot-wire probe, as well as surface flow visualization techniques. It was found that at low blowing rates, a cooling jet behaves very much like a normal obstacle and the mixing mainly takes place in the boundary layer. With increasing blowing rates, the jet penetrates deeper into the mainstream. The variation of the turbulence level at the inlet of the turbine cascade and the Reynolds number showed a strong influence on the mixing behavior. The kidney-shaped vortex and as an important achievement the individual horseshoe vortex of each single jet were detected and their exact positions were obtained. This way it was found that the position of the horseshoe vortex is strongly dependent on the blowing rate and this influences the aerodynamic mixing mechanisms. A two-dimensional code for the calculation of boundary layer flows called GRAFTUS was used; however, the comparison with the measurements showed only limited agreement for cascade flow with blowing due to the strong three-dimensional flow pattern.

The Influence of Load Distribution on Secondary Flow in Straight Turbine Cascades

This paper describes an experimental study of the three-dimensional flow within two highly loaded turbine cascades subjected to the same overall load but different load distributions. Data were obtained using pneumatic probes, pressure tappings, and a surface flow visualization technique. It is found that the general nature of the flow is similar for both cascades. In the exit plane the cascades show different spanwise loss distributions. However, the averaged secondary loss is quite similar in this plane. Examining the measurements farther downstream and also by comparing the calculated mixed-out values, it becomes clear that a higher magnitude of secondary loss is generated by the front-loaded cascade.

Three-Dimensional Flow in a Low-Pressure Turbine Cascade at Its Design Condition

This paper describes an experimental study of the three-dimensional flow within a high-speed linear cascade of low-pressure turbine blades. Data were obtained using pneumatic probes and a surface flow visualization technique. It is found that in general, the flow may be described using concepts derived from previous studies of high-pressure turbines. In detail, however, there are differences. These include the existence of a significant trailing shed vortex and the interaction of the endwall fluid with the suction surface flow. At an aspect ratio of 1.8, the primary and secondary losses are of equal magnitude.

A New Experimental Technique to Simulate Secondary Erosion in Turbine Cascades

In refineries, power-recovery turbines are widely used in the fluid catalytic cracking process to extract power from particle-laden gases. The gas particles impinging on the blades cause blade and platform erosion. This erosion can be broadly classified into primary and secondary erosion according to the dynamics of the particle/flow interactions and whether the damage is caused by direct inertial impingement or by recirculation of fine particles (1–2 μm) through the blade secondary flows, by the vortices induced by these flows. This paper reports on a new experimental method devised to simulate the secondary erosion patterns without the use of a dust-laden stream. In this method, blades coated with a sublimating material such as naphthalene are tested in a wind tunnel. The secondary flow vortices tend to increase the local rate of sublimation in those areas where surface momentum gradients are high. This simulates the condition of preferential erosion induced by the dust loading present in the vortices. Tests show the induced patterns to be quite akin to secondary erosion seen on field run blades especially in the critical erosion patterns seen near the blade roots. Design modifications were then successfully developed to minimize this secondary erosion. These were shown to have a capability of reducing the erosion by 50 to 75 percent, by utilizing platform step control and naturally induced boundary layer suction. Conversely, many other features were found surprisingly ineffective. The method was also shown to be a very effective surface flow visualization technique for internal and external surfaces. Of the approaches found to be successful in minimizing erosion damage, control of the geometry of the stator to rotor steps along the hub flow path blade platforms was critical. Steps in general have the effect of making erosion worse. The most successful approach is the introduction of an inherent suction slot and the suction flow passage between individual blade platforms.