This paper deals with measurement-integrated (MI) simulation, which is based on the observer in dynamical system theory to obtain the exact and detailed information of real flows. In this study, we propose the MI simulation coupled with Particle Image Velocimetry (PIV) for a flow with the Karman vortex street behind a square cylinder at Reynolds number of 1200 based on the cylinder width. The validity of the PIV-MI simulation is first examined in two-dimensional numerical experiment. The effect of feedback data rate is investigated by changing the feedback frequency and the feedback area. Then effectiveness of the PIV-MI simulation is validated in experiment. As a result, the PIV-MI simulation with full feedback shows good agreement with the standard solution for both the mean velocity and the velocity fluctuation. From the viewpoint of the reduced feedback data rate, spatially limited feedback shows better results than temporarily limited feedback. It is also confirmed that the information around the cylinder is important to reproduce the wake behind the cylinder. In the result of the experimental validation, the PIV-MI simulation reproduces the experimentally obtained flow field, showing the same effect of the feedback in accordance with the numerical experiment.
In this research, the wake turbulence from actual passenger airplanes taking off from Sendai airport was measured with Electronic Navigation Research Institute's Doppler laser radar (lidar). First, the influence of the surrounding wind on the behavior of wake vortices was investigated. The wake vortices in the crosswind case disappear more quickly from the runway than those of the low surrounding wind and head wind cases. In addition, the wake vortices in the case of large crosswind move faster than those in small crosswind. Next, the correction factor was estimated by using the pseudo lidar measurements based on Computational Fluid Dynamics (CFD). The corrected data for weak surrounding wind case agreed with the existing wake vortex model.
Subcooled cryogenic fluids are used in many fields such as a propellant for liquid propulsion rocket systems and a coolant for superconducting systems. However, the fundamental characteristics of subcooled cryogenic cavitating flows have not been clarified. Therefore, a visualization experiment for a cryogenic cavitating flow passing through a converging-diverging nozzle was carried out with liquid nitrogen in the subcooled condition. The results indicate that the cavitation instability is caused by the intersection of the speed of sound in a gas-liquid two-phase flow with the required velocity for cavitation inception and cavitation conservation.
Numerical simulation of wake turbulence was performed by integrating the lidar measurements using four-dimensional variational method. A bogus vortex technique was adopted to ensure the existence of wake vortices in the flow field. The validation of the method was performed by an idealized test case using virtual lidar measurement which was produced by the reference simulation of a vortex pair. The results of the validation showed the convergence of a vortex parameter such as a circulation to the parameter of reference simulation case. It was also confirmed that the velocity distribution on a measurement plane agreed with reference one.
Large-eddy simulation (LES) is applied to the problem of plume dispersion in the spatially-developing convective boundary layer (CBL) capped by a temperature inversion. In order to generate inflow turbulence with buoyant forcing, we first, simulate the neutral boundary layer flow (NBL) in the driver region using Lund's method. At the same time, the temperature profile possessing the inversion part is imposed at the entrance of the driver region and the temperature field is calculated as a passive scalar. Next, the buoyancy effect is introduced into the flow field in the main region. We evaluate the applicability of the LES model for atmospheric dispersion in the CBL flow and compare the characteristics of plume dispersion in the CBL flow with those in the neutral boundary layer. The Richardson number based on the temperature increment across the inversion obtained by the present LES model is 22.4 and the capping effect of the temperature inversion can be captured qualitatively in the upper portion of the CBL. Characteristics of flow and temperature fields in the main portion of CBL flow are similar to those of previous experiments, and observations. Concerning dispersion behavior, we also find that mean concentrations decrease immediately above the inversion height and the peak values of r.m.s concentrations are located near the inversion height at larger distances from the point source.
In vitro blood vessel biomodeling with realistic mechanical properties and geometrical structures is helpful for training in surgical procedures, especial those used in endovascular treatment. Poly (vinyl alcohol) hydrogel (PVA-H), which is made of Poly (vinyl alcohol) (PVA) and water, may be useful as a material for blood vessel biomodeling due to its low surface friction resistance and good transparency. In order to simulate the mechanical properties of blood vessels, measurements of mechanical properties of PVA-H were carried out with a dynamic mechanical analyzer, and the storage modulus (G’) and loss modulus (G”) of PVA-H were obtained. PVA-Hs were prepared by the low-temperature crystallization method. They were made of PVA with various concentrations (C) and degrees of polymerization (DP), and made by blending two kinds of PVA having different DP or saponification values (SV). The G’ and G” of PVA-H increased, as the C or DP of PVA increased, or as the proportion of PVA with higher DP or SV increased. These results indicate that it is possible to obtain PVA-H with desirable dynamic viscoelasticity. Furthermore, it is suggested that PVA-H is stable in the temperature range of 0°C to 40°C, indicating that biomodeling made of PVA-H should be available at 37°C, the physiological temperature. The dynamic viscoelasticity of PVA-H obtained was similar to that of the dog blood vessel measured in previous reports. In conclusion, PVA-H is suggested to be useful as a material of blood vessel biomodeling.
Background and purpose: Stenting is one of the treatment options for carotid artery stenosis. To show the effectiveness of the treatment, computational fluid dynamics (CFD) has been performed for the last several decades. The inlet/outlet boundary conditions are important in CFD, and several researchers have used various inlet/outlet boundary conditions. In this paper, we compared the blood flow with various inlet/outlet boundary conditions and the measurement data obtained by an ultrasound device. Methods: Blood flow speed was measured in the internal carotid artery (ICA), the external carotid artery (ECA), and the common carotid artery (CCA) using an ultrasound device. A carotid artery was reconstructed by computed tomography (CT). Mesh in the integrated data was generated to perform flow dynamics using a commercial code. CFD for blood flow was performed using the reconstructed carotid artery. Five cases of inlet and outlet boundary conditions (I/O B.C.) were used for the CFD. The simulation results were compared with the ultrasound data on the blood flow speed in the vicinity of the center of the ICA and the ECA. Results: Various blood flow speeds were obtained from the five cases. The case of adjustment of pressures in ICA and ECA is the nearest flow speed to the ultrasound data. Conclusion: The flow speed depends on the I/O B.C.. The I/O B.C. may be necessary for the measurement data obtained by ultrasound device or magnetic resonance imaging (MRI).
This paper introduces our own hierarchical data visualization technique, HeiankyoView, and discusses its potential for fluid science. HeiankyoView represents hierarchy as nested rectangles, and displays thousands of data elements in one display space. The paper briefly introduces the algorithm and various applications of HeiankyoView, and discusses our attempts for visualization of computational fluid dynamics data. Finally, the paper introduces our work on visualization of atomic plant data using HeiankyoView.
In this paper, we present a volume rendering framework for visualizing 3D flow fields. We introduce the concept of coherence field which evaluates the representativeness of a given streamline set for the underlying 3D vector field. Visualization of the coherence field can provide effective visual feedback to the user for incremental insertion of more streamline seeds. Given an initial set of streamlines, a coherence volume is constructed from a distance field to measure the similarity between the existing streamlines and those in their nearby regions based on the difference between the approximate and the actual vector directions. With the visual feedback obtained from rendering the coherence volume, new streamline seeds can be selected by the user or by a heuristic seed selection algorithm to adaptively improve the coherence volume. An improved volume rendering technique that can render user-defined appearance textures is proposed to facilitate macro-visualization of 3D vector fields.
Multi-Objective Optimization has been applied to a design problem of the twin engine concept for Silent Supersonic Business Jet (SSBJ). This problem aims to find main wing, body, tail wing and engine nacelle configurations, which can minimize both sonic boom and drag in a supersonic cruising flight. The multi-objective genetic algorithm (MOGA) coupled with the Kriging model has been used to globally and effectively search for optimal design candidates in the multi-objective problem. The drag and the sonic boom have been evaluated by the computational fluid dynamics (CFD) simulation and the waveform parameter method. As a result, the present optimization has successfully obtained low-boom and low-drag design candidates, which are better than the baseline design by more than 40% regarding each performance. Moreover, the structure of design space has been visualized by the self-organizing map (SOM).
We propose a novel interactive parameter optimization technique which asks users to determine whether further exploration is required by using a hierarchical visualization technique. Our technique generates a k-d tree and uses the coefficient of multiple determinations (R2) for tree-branching; however, this requires a huge amount of computation since it processes the response surface at every leaf node of the k-d tree, including those that may not have minimum parameters. To solve the problem, we introduce human evaluation of the display on the computer screen, in which every tree-node is evenly displayed regardless of its hierarchical level. We confirmed the effectiveness of the proposed technique by searching for pre-determined parameters in some test functions and biological cell simulation results.