Papers by Keyword: Flow Visualization

Abstract: With Eulerian Method of Moment (MoM) solvers for the CFD simulation of multi-phase fluid flow, the positions of bubbles or droplets are not modeled explicitly, but through scalar fields of moments. These fields can be interpreted as probability density functions describing the distribution of bubble locations. To enable intuitive visualization that allows direct visual comparisons between simulation and physical experiment, explicit instances of the bubble distribution are required. In this work, we examine one sampling-based method for obtaining sets of bubble positions from density fields. Based on an example dataset, we study the influence of the main parameter, the kernel size, on the resulting bubble set. We identify a tradeoff between numerical accuracy and temporal continuity for the visualization.

Abstract: In this paper the wind tunnel at the University of Applied Sciences Stralsund and few construction details as well as the calibration of the nozzle are presented. Furthermore some approaches to visualization and measurement of velocity fields of a simple body of vehicle are shown. The wake structure behind of simple car models was investigated experimentally using Particle Image Velocimetry (PIV). Furthermore the visualization of flow field by the fog probe systems supports the evaluation of the flow and drag behavior.

Abstract: A synthetic jet (SJ) is a fluid jet flow generated from fluid oscillations during a periodical fluid exchange between an actuator cavity and surrounding fluid. A water synthetic jet was generated from submerged piezoelectric-driven SJ actuator. The actuator slot width was 0.36 mm. The experiments were performed using laser induced fluorescence (LIF) flow visualization and particle image velocimetry (PIV) techniques, both in a phase locked setup. The LIF visualization was used to demonstrate three-dimensional nature of the SJ formation process and to estimate SJ velocity. The PIV experiment quantified SJ velocity cycles in chosen plans. The driven frequency was adjusted near the resonance at approximately 46 Hz. It was evaluated theoretically and confirmed experimentally by means of LIF visualization. The time-mean orifice velocity and the Reynolds number were estimated as U₀ = 0.07–0.10 m/s and Re = 100–150, respectively.

Abstract: Experimental details of the flow field and wake over airfoils and 2-D wings are time and cost consumption. In this study, the flow visualization technique was adopted to investigate the flow field surrounding NACA4412 airfoil. The investigations were carried out in smoke tunnel, operating at low Reynolds number in a range of 10⁵. The airfoil was tested in two operational cases: first as clean wing and the second as under-loaded wing by attached missile model. The experiments were conducted at various angles of attack as 0⁰, 5⁰,10⁰, 15⁰ and 20⁰. It was found that the under-load of external body under the wing is influencing the flow structure over the wing. Also, the wake after the external body is swirling, leading to very complicated wake interaction. The results from the work can support the numerical simulation and the prediction of the laminar to turbulent transition and the separation and wake interaction of high lift airfoil flow fields.

Abstract: This paper describes the testing of wind turbine blades with tubercles in two different ways: outdoor testing and flow visualization. In the outdoor testing, the tubercle pitch was varied for turbine blade lengths of 30 cm, 40 cm, and 50 cm. The pitch-to-length ratio of approximately 1/10 to 1/16 produced the most power output. In flow visualization, both tubercle pitch and amplitude were varied. Vortices created behind the tubercles were shown to increase lift by minimizing flow separation.

Abstract: The aim of this paper was to present a method to identify the extent of cavitation in pump using the photographic records of cavitation tests conducted on pumps having three different leading edge profiles of the vane. Based on the extent of cavitation in pump, the impeller with circular leading edge was found to be better in operation, followed by plain and ellipse2 leading edge impellers. The technique adapted here was useful to correlate the extent of cavitation with the head drop in pump.

Abstract: A numerical simulation has been carried out to study the effects of twin inclined side mass injection with cross flow through a circular duct using modified model, considering streamline curvature effects by modifying the model constants. 1/7^th turbulent velocity profile has been taken at the inlet. The effects of side mass injection on the flow pattern of the main bulk fluid and the mixing of two mutually cross turbulent flows have been studied in details. The formation of recirculatory flow has been visualized by varying the primary as well as secondary injection angle. With the variation of the injection angle axial velocity profiles at various locations and the centerline velocity variation along the duct have been studied. It has been observed that the impact of primary injection angle variation on the recirculation size is more than the secondary injection angle variation.

Abstract: Fine instantaneous flow structures of different scales around a blunt cone with or without supersonic film cooling were visualized via nanotracer planar laser scattering (NPLS), which has a high spatiotemporal resolution. The Mach number of the freestream is 3.0 and 3.8 respectively and the air injection is at Mach 2.5. Lots of typical flow structures were visible clearly, such as shock wave, expansion fan, shear layer, mixing layer, K-H vortices and turbulent boundary layer. With injection, the model wall surface can be covered by a thin film layer. While no injection, the flow is similar to the supersonic flow over a backward-facing step and the structures are simpler relatively and there is a longer laminar region. Flow structures with or without film cooling at Mach 3.0 and 3.8 were compared.

Abstract: The particle tracking velocimetry (PTV) algorithm is one of the most important branches in the flow visualization research. An efficient two-frame PTV based on Delaunay tessellation was updated by a novel concept called Dual Computation. The updated algorithm was tested using CFD flows with changeable parameters and random erasing of particles as perturbation. In addition to the simple structure and the minimal dependence on algorithmic assumptions, the advantages of this updated algorithm also include the high accuracy in addressing complex flows with noticeable ratio of particles having no match.

Abstract: In this study, a visualization experiment was performed in order to confirm the flow pattern around airfoil with relative velocity fluctuation by in-line forced oscillating in the direction of flow. An airfoil NACA0012 with attack angle of 5 degrees produce the separation in the steady state was observed by the experiments using dye streak method at Reynolds number Re=3.6x10³. The investigation of the attack angle which does not separate in such low Reynolds number was performed, and it was confirmed that the separation occurs to 3 degrees. And the airfoil with attack angle of 2 degrees which does not cause separation in steady state, was forced to oscillate with two kinds of relative velocity ratio (umax/U=0.4 and 0.8, here, umax and U denote maximum moving speed of airfoil and main flow velocity, respectively.). The flow separation on the surface of airfoil with attack angle which does not produce the separation in the steady state is occurred even if the maximum moving speed of airfoil umax is in the range which does not exceed main flow velocity U.