Scale modeling based on static and dynamic similarity has been widely used with high-speed photography techniques for motion pictures to reproduce unrealistic world. Focusing on video works created by SFX as examples of scale modeling experiments, this paper attempts to explain the scale modeling theory, so called “Law approach” which is a method to derive the scaling law based on deep physical insights. To accomplish this, the falling motion of an object in fluid is taken up as the simplest but frequent case. The governing equation of the phenomenon is considered, and the magnitude of each term is estimated. A quantitative comparison demonstrates which factor is most significant in that phenomenon. Though it seems a relatively complicated explanation, it is believed that this approach gives a clear insight into how the dominant factor(s) is extracted in the Law approach.
The depletion of the iron and energy resources is imminent; however, the urgency is yet to be realized. Iron and energy resources are indispensable for the development of social infrastructure within the nation. A new recycling society via renewable energy for this industry can be built by solid biofuel with high-temperature characteristics. The development of a new bio-solid melting furnace using renewable energy to construct a modern recycling society is essential for obtaining economic stability over the long term. This article considers the combustion characteristics of a small melting furnace using biocoke, which is one of solid biofuel with high-temperature characteristics and conducts a similar rule for scale modeling. This article also describes the importance of research and development to maintain the national and living infrastructure by solid biofuels, even if fossil resources deplete.
A Scale modeling was derived by Emori (Professor Emeritus, Seikei University) based on traffic engineering. A model experiment is to investigate the phenomenon by replacing a simple system due to a complex phenomenon. When a scale model is applied, the consideration coming from extrapolation is often conducted. Basically, extrapolation is inadequate for dealing with experimental data. However, scale models are considered to include substantial reasons for extrapolation to some extent. The useful range of certain scale models is examined in this article. In addition, the concept of energy π number is suggested. The energy π number is a new idea for solid biofuel, and to introduce its characteristics by the strength of materials and combustion behavior to understand new solid biofuel.
A similarity law between water channel experiments and wind tunnel experiments was newly proposed using the Reynolds and Shields numbers for laboratory studies concerning the mechanisms of sediment transport and channel variation in alluvial rivers. Effectiveness of the similarity law was verified through the comparison of the laboratory data. Numerical values of representative flow velocities and sand grain diameters in classical water channel experiments, for ripples, dunes and alternate bars, were converted to those in wind tunnel experiments through the use of the above similarity law. The converted flow velocities were in the specs of standard wind tunnel apparatus, and then, the converted sand grain diameters were easily obtainable sizes. In conclusion, it was shown that wind tunnel experiments were substitutable for water channel experiments in river sedimentation engineering.
This paper considers the scaling laws of hot-surface ignition of combustible gases. Premixed stagnation flows impinging on hot surfaces were theoretically analyzed. Dimensional analysis was first conducted to identify a Damköhler number as the key parameter that controls ignition. Basic equations were then numerically solved to obtain the critical conditions for ignition. It was confirmed that ignition occurs when the heat flux from the hot surface to the gas phase exceeds a critical value. The obtained dependence of critical heat flux on the Damköhler number indicated the importance of thermal inertia in the gas phase. It was also found that the critical hot-surface temperature for ignition decreases with an increase in the Damköhler number. The dependence of critical temperature on the Damköhler number is nevertheless weak especially when the Damköhler number is large. This result suggests that the minimum ignition temperature (MIT) be used for safety-management purposes.
A novel apparatus simulating the global warming mechanism and attendant variations in the global mean temperature was developed. The apparatus was designed so that the surface temperature of a model Earth was determined solely by a suitably simulated radiative energy balance. In simple experiments using acrylic plates as a layer of greenhouse gases, the steady state temperature was found to decrease with increasing plate thickness beyond 1 mm. However, this demonstration didn’t provide an accurate simulation because the energy loss and heat capacity were affected by the thickness and the pressure effect of the gas layer couldn’t be simulated. An improved system was devised, incorporating supplies of gaseous CO2 and N2, and experiments were carried out using both high and low CO2 concentrations. The resulting temperature increases based on the greenhouse effect were 0.7 and 0.3 °C, respectively. These data showed that the extent of warming varied with the CO2 concentration, although the concentration was artificially high and the atmosphere in the model was not homogeneous. Various improvements, such as the use of a more powerful cooling system and the addition of a metered gas supply unit, allowed the apparatus to more accurately demonstrate temperature changes corresponding to gas composition.
The boundary layer and velocity shear layer that develop around a circular cylinder placed in a flow have a significant effect on lift and drag depending on whether it is laminar or turbulent. These shear layers are so thin that special measures are required for the experiment. In this study, a specially shaped probe was developed to measure the boundary layer using a hot-wire anemometer. An experiment was performed using with that probe at Re = 1.6×104. As a result, the velocity distribution and the velocity fluctuation distribution of the extremely thin boundary layer of 0.5 mm were measured. The frequency analysis showed that the separated laminar shear layer transitioned to turbulent flow near the boundary with the separated region.
In order to ensure the in-line measurement of the deformation state of a woven fabric in a production process, the present paper proposes a measurement method for the textile deformation by the digital image correlation (DIC) method with each interlace point of the warp and weft as a measuring point. In the proposed method, utilizing the periodic weave of woven fabric, each interlace point of the warp and weft in the initial image is detected by the template matching. Detecting individually the interlace points on the warp and weft can evaluate the textile deformation based on the warp and the weft. Furthermore, the time change of the displacement of each detected interlace point as a measuring point can be measured by the DIC method. In the DIC method, by using the calculated yarn density, the searching area in which a subset image is swept to evaluate the correlation coefficient, is set to prevent the false detection due to the periodic weave. Conducting an experiment simulating the conveying a weave fabric, the spatial distributions and time changes of the oriental angle, stretch ratio and yarn density of the weave sample are measured to reveal the usefulness of the proposed method.
The information on the frequency characteristic of the internal circulation flow can be useful in determining the cause of fluid noise and vibration problems in the torque converter. In this paper, the internal flow field of an automotive torque converter is experimentally visualized, and the velocity field is measured using particle image velocimetry (PIV) in the cases of the speed ratio 0.1 and 0.7. The time series of the internal circulation flow is investigated to analyze the unsteady flow field due to the flow interactions between cascade blades of impeller, turbine, and stator. It is found by using FFT analysis that the frequency characteristics of flow rate have remarkable peak values at the blade passing frequency, its harmonics of each cascade, and combined frequencies. It was experimentally confirmed that the frequency characteristics of the internal circulation flow in the torque converter are similar to that of the multi-stage turbomachines.