In order to study the mechanism of the vehicle interior noise induced by the flow around the automobile, the near sound field around the rearview mirrors and the A-pillars is usually focused. As the difference in scale and intensity, in the near sound field, the pressure fluctuations related to the hydrodynamics and the acoustics can be considered as two different phenomena. After dividing these two phenomena by decomposition method, as the pressure fluctuations affect the interior noise through the glass transmission, the pseudo sound should not be neglected. By calculating the Ligthill Equation (LE) to show the sound field, the pseudo sound can be observed in the near sound field. On the other hand, the Acoustic Perturbation Equation (APE) can be used to show the sound field without pseudo sound. By comparing the results of LE and APE, we can evaluate the pseudo sound quantitatively. At the same time, by performing the wavenumber-frequency spectrum analysis, flow field, sound field, pseudo sound, apparent sound can be distinguished in different wavenumber regions and their contribution to the interior noise can also be evaluated.
In order to decompose hydrodynamic pressure fluctuations (HPF) and acoustic pressure fluctuations (APF) around the automobiles, a MESM microphone array and internal model for wind tunnel experiments were developed. A small array can be created by using a MEMS microphone. As a result, pressure fluctuation around an automobile can be divided into HPF and APF by performing wavenumber-frequency analysis using the developed MEMS microphone array. On the surface of the vehicle body, the sound pressure level was proportional to the sixth power of the wind velocity, and it was confirmed that a dipole sound was generated. On the other hand, the pressure level of the flow fluctuations was proportional to the fourth power of the velocity. It is revealed that the developed MESM microphone array is an effective tool for decomposing HPF and APF.
In order to identify vortex center axes around the vehicle from the result of computational fluid dynamics, a method focusing on the pressure minimum is proposed. The sectional-pressure-minimum-and-swirl method can identify vortices that are low pressure at center points and swirling in homogeneous isotropic turbulence. In this paper, it is extended to be applicable to the flow field around vehicles with unstructured grids in three steps. First, spherical projection method is used to determine whether the vortex center point is inside or outside an unstructured grid of various shapes. Second, a vortex center axis grows in two directions, the front and the back a plane perpendicular to the vortex axis and imposes two angle conditions to prevent fragmentation. Finally, the vortex center axes are filtered by the number of vortex center points. In order to verify the effectiveness of the proposed method, some vortex identification methods were used for the flow field around the sedan. The flow filed was a time-averaged flow field calculated by large eddy simulation. As a result of comparing to the previous method, the proposed method prevented fragmentation of vortex center axes. The proposed method could identify four known vortex structures obtained by the isosurface method. Compared to another commonly used methods, the proposed method did not connect the vortices and briefly visualized the vortex center axes.
Among pressure-sensitive paint measurement techniques, the lifetime imaging method is attracting attention because it can measure pressure distribution only from wind-on images without wind-off ones. It can prevent an error caused by the image registration between wind-off and wind-on ones. The luminescence lifetime of PSP is expected to be uniform on the model under uniform pressure and temperature conditions. However, it is not actually uniform and is a major error factor in the lifetime imaging method. Therefore, we have investigated the causes of the non-uniform distribution of the luminescence lifetime of PSP on the model. Especially we focused on the effect of dye solvents on the binder structure and the uniformity of luminescence lifetime. The obtained results revealed that, the standard deviation of the luminescence lifetime was lowered when the mixing ratio of the polymer dissolving solvent was increased. This is because the dye was more uniformly distributed in the polymer.
This paper describes numerical aeroacoustics simulation of fan noise for the bi-directional rotating electric motor. For solving aeroacoustics, we took into account transient compressible flow and turbulent flow. Moreover for solving turbulent flow, Large Eddy Simulation (LES) was used. The fundamental motor structure was constructed to verify the prediction accuracy of our numerical simulation model. Also, we measured not only the sound pressure level in the free space but also pressure fluctuation on the sound source area where is downstream of the fan in this study. Predicted sound pressure level and fluid pressure fluctuation at different rotational speed are in good agreement with the experimental result.
The aim of this investigation is to estimate drag force acting on a bicycle helmet and power required for wind speed of bicycle race. It is known that a helmet of bicycle race has not only role to protect the head but also reduce aerodynamic drag force. Since the required power of caused by aerodynamic force acting on the helmet and head is about 18% of the total power of cycling, development of the low drag force helmet is required. To evaluate and understand the unsteady aerodynamic force and its generation mechanism, LES analysis was performed. As a result, the streamlined shape helmet placed in straight against the flow has low drag, but the drag force rapidly increases in the posture during goal sprinting. Therefore, the power required for top speed of bicycle race is more than three times that in steady state. Since, the flow around the helmet is unsteady, the maximum fluid force reaches 3.5 times that of the average. For this reason, it is required to develop robust shape helmet against changes in posture with small fluctuating drag force.
When using small fans to cool electronic products, it is known that fan aerodynamic noise varies with the flow channel structure upstream of the fan. Fan noise prediction considering air duct structure of electronic product is complicated and difficult. In this study, increase fan noise due to the influence of intake louver shape was analyzed using numerical calculation. When the air intake is slant louver, flow velocity distribution upstream of the fan is non-uniform. Attack angle of the fan blade and fluid force acting on the fan blade fluctuate greatly at the rotational frequency, it turns out that it increases blade passing frequency noise.
In this study, The reduction rate of rotation speed was investigated by a hydraulic test. As a result, it was found that the eccentric shaft could reduce the rotational speed from 8.2% to 9% and The loss factor was found to be reduced by 33%.Also the internal flows were clarified by PIV .The driving condition in the PIV was 2.0 L / min at 10000 rpm, and axial velocity distribution was measured and compared.
In order to improve the response time of fast-responding pressure-sensitive paint, it has been considered that the overcoating of the dye solution on a pre-coated porous binder layer consisting of a polymer and particles is effective. This is because this overcoating method may distribute the dye near the surface of the binder layer; it reduces the apparent binder thickness. However, it was found that the polymer in the pre-coated binder layer was dissolved by the solvent of the dye solution and moved to the surface and covered the porous structures. It lowers the responsiveness of PSP. Therefore, we have investigated conventional “one-component” PSP again to avoid the above phenomena. We studied the influence of the particle diameter and spraying method on the responsiveness of PSP. As a result, “one-component” PSP achieved a response time of 16 μs by using TiO2 having a small particle diameter of 30 nm at particle ratio of 93 wt%.
In this study, local skin friction was measured on the suction surface of the airfoil by using the oil film interferometry (OFI). The airfoil model had NACA0012 wing section and the airfoil flow condition was under the lifting condition of Re=8.0×104. OFI was performed with adjustment of angle of light source and camera for local airfoil surface. It was found that the adjustment affected measurement accuracy of local skin friction. The measured local skin friction had difference of less than 2% compared to the LES results by Miyazawa et al.1).
In a high temperature gradient environment, the nanoparticles often deposit on the wall of the fluid machine due to the thermophoretic effects, resulting in energy loss. Even in a cooler of an exhaust gas recirculation system for an automobile engine, energy loss and a decrease in cooling performance are problems due to the nanoparticle deposition phenomenon. In this study, the effects of the attack angle of the cooling plate on the flow field and the nanoparticle deposition phenomenon were investigated by numerical simulation of the rectangular duct flow with the cooling plate installed. As a result, it was found that when the attack angle was changed from 0 to 90 deg, the pressure loss increased as the attack angle increased, and the heat transfer coefficient tended to increase as the attack angle increased. In addition, a vertical vortex with an axis in the main flow direction and a horizontal vortex with a wide recirculation region, where the flow tends to stagnate, were observed. The lateral vortex is superior in terms of heat transfer characteristics, and the vertical vortex has a trade-off relationship that reduces pressure loss compared to the lateral vortex. In addition, the nanoparticle deposition process did not change regardless of which vortex occurred, but when the vertical vortex occurred, the deposition layer thickness increased.
Eddy scale what is one of indices for evaluating the turbulent flow field is calculated from cross-correlation, auto-correlation, energy spectrum, half width etc...The difference in practicality due to these calculation methods was verified by comparing them quantitatively using experiments data which measured by wind tunnel experiments. In the experiment, the NACA0012 airfoil with a chord length 150mm, an aspect ratio of 4.27, and a span length of 870mm was used, and the average flow velocity, velocity fluctuation, energy spectrum, auto-correlation and cross-correlation of the far wake of the blade were measured using a hot wire anemometer. The measurement was performed two-dimensionally. From the experimental results, it is considered that the wake of the blade flows while maintaining the structure even at a distance of 13 times the chord length (X/C=13). From the correlation coefficient distribution chart, the eddy structure at the position of X/C=10 was identified no uniform isotropic. The eddy scale calculated from auto-correlation has a certain level accuracy, but cannot be said to be practical. The eddy scale accuracy what calculated from the half-width and power spectrum length were proven exceedingly bad, and practicality is poor.
We are promoting cooperation of fluid simulation, rapid prototyping and evaluation, focusing on 3D-CAD data, for blowers that are products based on motor technology. Parallelization and multi-case of simulation are realized by using open source software for fluid simulation. By using a 3D printer that uses materials such as powder and photo-curing resin for trial production, shortening of the period is realized. By using a 3D printer that uses materials such as powder and photo-curing resin for rapid prototyping, we realize shortening of the evaluation period. As an example, we show the comparison of the characteristics of a real product and a rapid prototyping by the 3D printer in a small (about 100 mm in diameter) and high-speed (about 15,000 revolutions per minute) centrifugal blower. Also, we show visualization of flow simulation results for the same products.