For suppression of time periodic flow and normal stress using optimal design techniques, this paper presents an optimal shape by sensitivity based on the Generalized J Integral, and makes a comparison to results of sensitivity evaluated by boundary and volume integrations of a type that is widely used for shape optimization problems. To date, J integral has been used to evaluate the energy release rate of stress concentrated near cracks or corners in the field of fracture mechanics. The Generalized J integration type used for this study is sensitive to avoid singularity and to engender the suppression of stress concentration in the domain and at the boundary. For such shape optimization studied here, the cost function is defined as eigenvalues with modes of the time fluctuation component in Snapshot POD. The main problems are the Reynolds Average Navier–Stokes problem and eigenvalue problem of Snapshot POD. An objective functional is described using Lagrange multipliers and finite element method. The sensitivity is obtained in three kinds of ways, the boundary and volume, the Generalized J integration types. Numerical results reveal that the cost function is minimized as the time periodic flow is suppressed in such the three ways. Especially, normal stress on the boundary in the sensitivity evaluated by the Generalized J integration type is suppressed most of them.

Coarse-graining is indispensable for extracting a hierarchy of vortices in fully developed turbulent flow with multiscale nature. In the present study, for a high-Reynolds-number turbulent boundary layer, we employ two simple coarse-graining methods in real space; namely, a Gaussian filter and the combination of the Gaussian filters at two scales. The former corresponds to a low-pass filter of Fourier modes, while the latter corresponds to a band-pass filter. We also examine two different filter widths for the band-pass filter. Then, we show difference in the statistics of the three filtered fields. Since the velocity gradients in turbulence are mainly determined by the smallest-scale motions, vortical structures identified by the second invariant Q of the velocity gradient coarse-grained by the filters are similar. However, there is difference between low- and band-pass filtered fields in the contribution to the enstrophy production rates. This is because the production rates are determined not only by the magnitude of the strain rates but also by the alignment between the vorticity and the stretching direction. In addition, since vortices are not created in the entire system, the conditional sampling by the value of Q is essential to understand the generation mechanism of the hierarchy of vortices. The conditional analysis of the band-pass filtered fields demonstrates that small-scale vortices in the log layer are stretched by twice-larger vortices, whereas they weaken the twice-larger vortices. This observation is consistent with the picture of the energy cascade. We also show that when using the band-pass filter, these conclusions are robust irrespective of the choice of the filter width.

We redesigned the Mars Airplane Balloon Experiment Two (MABE-2) based on MABE-1 to improve the vehicle’s stability and controllability. Following the redesign, the MABE-2 vehicle had a larger horizontal tail volume than that of MABE-1 for improved stability performance. In addition, to further improve the stability and control characteristics, a rectangular planform was employed for the horizontal tail wing; in contrast, MABE-1 had a tapered planform. The vertical tail position of MABE-2 was moved to the end of the horizontal tail wing, because the vertical tail of MABE-1, which was positioned at the mid span of the horizontal tail wing, showed aerodynamic interaction with the horizontal tail wing. In this paper, we discussed the aerodynamic performance of a control surface based on computational fluid dynamics with variation in the deflection angle between the control surface and the horizontal tail (elevator), and we examined the effects of this redesign on longitudinal control characteristics. Numerical investigations confirmed the linear variation in the pitching moment and the aerodynamic force with the changing elevator deflection angle in MABE-2. Surface pressure observations indicated that MABE-2 shows a smooth variation in the pressure distribution with changing elevator deflection angle, while MABE-1 does not. These results demonstrate that the aerodynamic control characteristics of MABE-2 were improved in comparison to those of MABE-1.

Corrugated wings, which are cross-sectional shapes of dragonfly wing, are expected to improve aerodynamic performance due to vortices generated by irregular shapes at low Reynolds number region. It is difficult to observe the influence of vortices generated from the unevenness of the shape by experiments. In this research, the flowfields around corrugated wings were calculated using Cartesian mesh-based Computational Fluid Dynamics (CFD), Building-Cube Method (BCM). The simulation grasped the detailed flowfield, which was difficult to be visually observed by the experiment. From the visualization result, it is found that the flow circulation velocity inside the concave and convex surface is not accelerated but slow. The result indicates that the improvement in aerodynamic performance is caused by the shape and position of unevenness.

An analytical approach to turbulence modeling based on the double-Lagrangian formalism is applied to turbulence modeling. Extending a selfconsistent closure theory of homogeneous turbulence, current approach allows us to derive a quadratic nonlinear viscosity form of the Reynolds stress without relying on empirical parameters. To examine the future possibility of the present methodology as practical modeling approach, a simple non-linear K -ε model is constructed, which is then applied to turbulent channel flow at a medium Reynolds number (Re = 590). With the help of conventional modeled equations for K and ε, the channel turbulence is stably calculated yielding reasonable agreements with a DNS.

The cooling process of a biological phantom using ice slurries with different geometries in a limited space was experimentally investigated. Ice slurry has recently been considered to as a solution to cool organs in the abdominal cavity efficiently and rapidly to suppress biological reactions during minimally invasive laparoscopic surgeries. However, previous studies have not focused on the interactions between ice slurry and biological tissues in the abdominal area. In this study, we aimed to investigate the effects of ice slurry geometry, enclosure width L_w, and mimic-blood flow rate Q_b on the cooling of a biological phantom using ice slurry in a limited space. We prepared the same volume of ice slurry using different geometries with an ice packing factor of 25 wt% using a scraper-type method to place on the phantom surface. We observed the melting behaviors of the ice slurries and measured the surface and core temperatures of the biological phantom. It was found that the supply methods of the ice slurry affected the cooling of biological tissues significantly. When the ice slurry width was the same as that of the enclosure, the ice slurry floated on the melted slurry and inhibited the cooling of the biological phantom. When the slurry width was small compared to that of the enclosure, the slurry remained in contact with the phantom, thus resulting in its efficient and rapid cooling. The mimic-blood flow promoted the melting of the ice slurry increased the heat flux on the phantom surface. However, the core temperature was not affected. Thus, the core temperature cannot be reduced unless the blood flow is occluded.

Ice slurry is a homogeneous mixture of small ice particles and a carrier liquid. It is widely used in many fields. Previous studies have gradually clarified its heat transfer in high ice packing factor (IPF). However, only a few studies have focused on the mechanism of heat transfer with low IPF in a cavity heated from below. The objective of this study is to experimentally clarify the melting heat transfer of ice slurry in a cavity heated from below with low IPF to develop a direct contact medical cooling system. To observe the melting behavior of ice slurry, the test section was made of acrylic resin (100 mm × 60 mm× 30 mm) and a silicone rubber heater that was used for heating under constant heat flux conditions. We measured the surface temperature of the heater and the liquid thickness. We showed that the melting process can be divided into three stages. In the first stage, heat conduction dominated the process of heat transfer and the temperature of the heater rapidly increased. In the second stage, natural convection heat transfer dominated the process of heat transfer that increased the melting rate of ice slurry and decreased the temperature of the heater. In the third stage, heat conduction dominated the process of heat transfer in the concentration stratification. This led to a decrease in the melting rate and an increase in the temperature of the heater. Our result also showed that the melting process of the ice slurry is slow enough to consider it the quasi-steady state in the range of 10⁴ < Ra* < 10⁷ as compared to the development of the velocity and temperature fields.

The objective of this study is to investigate thermochemical processes in the shock layer by shock-tube experiments. In this study, the temporal profile of radiation intensity is observed by time-resolved emission spectroscopy. The measured radiation profiles are compared with the calculated radiation profiles to validate the chemical reaction processes considered in the calculation. The measured radiation profiles are different from the calculated ones, especially in the region ahead of the shock front. The measured radiation intensities for N₂, N₂⁺, and N start to increase ahead of the shock front. On the other hand, the calculated radiation intensities start to increase at the shock front. This difference could be caused by precursor phenomena which are not considered in the present calculation. The details of precursor phenomena has not been clarified. However, the present study has indicated some of the interesting results. From the radiation profiles observed in the region ahead of shock front, electronic excitation of N₂, photoionization and photodissociation of N₂ are found to occur. It is also found that the radiation profiles between experiment and calculation differ in the shock layer, showing that precursor phenomena have a great influence on thermochemical processes in the shock layer. In future, thermochemical processes should be modeled by incorporating precursor phenomena.

In this study drag calculations were performed for an airplane cruising at transonic speed in a flow-field using two far-field methods. Subjected flow-fields in the calculations were computational fluid dynamics (CFD) results of Reynolds-averaged Navier–Stokes simulation (RANS) around a wing. The objectives were to establish effective means to utilize far-field drag methods and wake flow phenomena as well as report pseudo total enthalpy which peculiarly appeared in the CFD simulation results. The drag calculation was completed using four wake integration equations. The first originated from the equation of the momentum conservation law itself, the second was based on enthalpy variation, the third was based on entropy variation, and the last was a method for induced drag calculation. Drag values resulting from the integrations were compared to those via a near-field method commonly used in CFD. Through the computation and comparison of wake integration drag values, it was proved that the both far-field methods were able to predict a comparably accurate drag value compared to that of the near-field method. In addition, strange inappropriate total enthalpy (pseudo total enthalpy) generation was found in some regions where a flying airplane never affects flow behavior. In the wake integrations, the pseudo total enthalpy generation seems to compensate for the drag value via the first equation. The pseudo total enthalpy generation depends on far-field boundary locations. In summary, wake integrations are promising to provide useful information for accurate drag prediction.

The objective of the present study is to understand formation mechanism of metal oxide nanoparticles in thermal plasma. High-speed camera technique with appropriate band-pass filters was applied to visualize the precursors of the metal oxide nanoparticles. A multiphase AC arc was generated under atmospheric pressure of air with aluminum raw powder injection to synthesize aluminum oxide nanoparticles. Optical emission spectroscopy of the multiphase AC arc was performed to select the transmission wavelengths as 514.5 nm and 670.0 nm for emissions from aluminum vapor and aluminum monoxide, respectively. Dynamic behavior of aluminum vapor and aluminum oxide was successfully visualized by the high-speed camera observation with these band-pass filters. Relative intensities of aluminum emission to argon emission as well as aluminum oxide emission to argon emission were calculated to estimate relative number densities of aluminum vapor and aluminum oxide. Results clearly revealed that aluminum vapor mainly existed at the higher temperature region than 4,000 K, while aluminum oxide became dominant at the lower temperature region. These obtained results experimentally elucidated that aluminum oxide nucleates at first, and then aluminum oxide condenses onto the nuclei.

Burning experiments were conducted to better understand the fuel regression behavior in a swirling-injection end-burning hybrid rocket engine using paraffin wax/gaseous oxygen propellant. The oxidizer mass flow rate, grain diameter, and the distance between the oxidizer injector and the grain end-surface were the variable parameters taken as influencing the regression rate. The engine attained an overall axial regression rate as high as approximately 5 mm/s, whereas unstable combustion occurred with increasing burning time owing to low melting temperature of paraffin wax. The fuel grain with a diameter of 90 mm also resulted in unstable combustion caused by the initial shallow crack of the cast grain. The radial distribution of the local regression rate exhibited dependency on the radial position and had two peaks: close to the periphery and the middle of the chamber. From the analogy of the heat transfer at the end surface in a vortex flow chamber, the controlling parameter of the overall axial regression rate was derived. Since this parameter depends on the distance between the oxidizer injector outlet and the fuel grain end-surface, to hold the grain end-surface by using some kind of actuator is necessary to attain constant O/F combustion.