The effect of groundwater level on forced convection heat transfer from a cylinder of 1 m in diameter buried at a depth of 10 m is studied numerically. The porosity and permeability of the soil are fixed at 0.5 and 1.0 × 10 –11 m 2 , respectively, throughout the present study, while the inlet velocity U 0 and the position of the phreatic surface ( h ), measured from the center of the cylinder, are varied in the ranges from 10 –9 to 10 –3 m s −1 and from − 4 to 4 m, respectively. Under these conditions, the heat fluxes on the cylinder are computed numerically. Various approximate solutions are also proposed and compared with those obtained numerically. The heat transfer results are also presented in nondimensional form for generality. The paper is divided into three parts, depending on the relative positions of the phreatic surface to the heated cylinder. First, the heat transfer rates are analyzed when the phreatic surface is above the cylinder, so that the cylinder is completely submerged in the water. In the second case, the phreatic surface is assumed to lie below the cylinder, so that the cylinder is left in the water-free space. In the third case, the phreatic surface is in contact with the cylinder surface, so that the cylinder is partially submerged in groundwater. For the above respective cases, three different approximate analyses are presented, and their validities and limitations are evaluated in comparison with the numerical calculations.

An upswept aft section at the underbody in ground effect can improve the aerodynamic downforce of vehicles. In order to clarify the effect of the upswept aft section, a simplified vehicle with the upswept aft section is examined using Large Eddy Simulations. In the present study, four upsweep angles of the upswept aft section, i.e., θ = 0°, 5°, 10° and 15°, are investigated, where 0° corresponds to the original Ahmed body. It is found that the upswept aft section leads to an increase in flow rates through a cross-section between the underbody of the model and the ground. The high flow rate enhances strong negative pressures not only on the upswept aft section but also on a forward part of the underbody. In addition, induced vortexes are generated near both side edges of the upswept aft section. The induced vortex enhances the negative pressure on the upswept aft section close to the side edge because the vortex develops downstream, approximately along the side edge. In this study, the aerodynamic downforce for θ = 10° is the maximum because of the high negative pressure based on the highest flow rate and the strongest induced vortex. Furthermore, the relationship between the induced vortex and an effective cross-sectional area under the upswept aft section is examined and a blockage effect is discussed. Three-dimensional flows, such as the induced vortex and the underbody inflow, are found to increase the effective cross-sectional area because the three-dimensional flow should improve a flow uniformity in the mainstream direction.

A micro-machined thermal flow sensor called “Flow Vector Sensor (FVS)” can measure an airflow speed and its direction simultaneously. The FVS is extremely small, and hence it does not disturb flowfields around the sensor. In addition, since a response time of the FVS is very short, the FVS can measure unsteady flows. Therefore, the FVS is expected to be applied to flowfields over various objects such as automobiles. However, when the airflow speed is high, the sensitivity of the prototype of the FVS tends to be lower. In this study, we numerically examine heat transfer from the FVS to the airflow, in order to improve the sensitivity of the FVS in a high-speed airflow. First, we investigate the heat balance between the FVS and surroundings, in order to identify the cause of the lower sensitivity of the FVS. The heat transfer between the FVS and airflows is found to affect the sensitivity of the FVS, especially in the high-speed airflow. Second, we examine the effect of the size of the FVS, in order to discuss the design philosophy of the FVS. The heat transfer from the FVS to airflows is found to decrease with decreasing the size. Consequently, the small size of the FVS can improve the sensitivity of the FVS. These results should provide new insights into the design philosophy of a high performance FVS.

A micro-machined thermal flow sensor, i.e., “Flow vector sensor (FVS)”, can measure air-flow velocity and direction. We numerically examine heat transfer phenomena for the FVS, to clarify its thermal characteristics. The heat transfer from the FVS to air-flow is found to affect the measurement accuracy, especially in high-speed winds.

We have investigated the effects of the rotating blades of an upwind-type three-blade horizontal-axis wind turbine (HAWT) on the basic characteristics of aerodynamic forces acting on its tower by conducting improved delayed detached-eddy simulations (DESs). Three tip-speed ratios were considered for the operating conditions of the HAWT: λ = 3 (low), λ = 6 (optimum), and λ = 10 (high). The diversion of the flow approaching the tower by the rotating blades and the low-pressure region that formed downwind of the blades significantly affected the aerodynamic forces acting on the tower. For example, the azimuth angle around the tower at which the pressure reached a maximum at each height shifted significantly in the direction of the movement of the blade passing the tower because of the diversion of the flow by the blades. Fluctuations in the lift force of the tower were significantly larger than those in its drag force because of the low-pressure region downwind of the blades.

This work describes transient heat transfer characteristics from a horizontal heated cylinder at a uniform temperature, placed in a cylindrical container filled with cold water. The scaling analysis has demonstrated three different heat transfer regimes as the heat process advances with time. The times that differentiate the three regimes have been identified and derived as a function of the Rayleigh number and the geometric aspect ratio between the inner cylinder and the cylindrical container diameters. The numerical experiment has been performed in order to prove the correctness of the scaling analysis. It is shown that the results derived by the scaling analysis agree well with those from the numerical experiments.

This study investigated the flow characteristics around a cross-flow wind turbine. A wind tunnel experiment (WTE) was performed to measure the flow characteristics past the wind turbine when operating at the optimal tip-speed ratio of λ = 0.4. In addition, computational fluid dynamics (CFD) simulations were performed for the flow field around the wind turbine that was operating at tip-speed ratios of λ = 0.1, 0.4, and 0.7. The CFD approach was validated against the WTE measurements. CFD results confirmed that with an increase in λ, the velocity deficit was generally increased in the leeward of the return side of the wind turbine, while it was generally decreased in the leeward of the drive side of the wind turbine. It was also confirmed that with an increase in λ, the turbulence kinetic energy was generally increased in the leeward of the return side of the wind turbine, while it generally decreased in the leeward of the drive side of the wind turbine.

Entropic cosmology assumes several forms of entropy on the horizon of the universe, where the entropy can be considered to behave as if it were related to the exchange (the transfer) of energy. To discuss this exchangeability, the consistency of the two continuity equations obtained from two different methods is examined, focusing on a homogeneous, isotropic, spatially flat, and matter-dominated universe. The first continuity equation is derived from the first law of thermodynamics, whereas the second equation is from the Friedmann and acceleration equations. To study the influence of forms of entropy on the consistency, a phenomenological entropic-force model is examined, using a general form of entropy proportional to the $n$th power of the Hubble horizon. In this formulation, the Bekenstein entropy (an area entropy), the Tsallis-Cirto black-hole entropy (a volume entropy), and a quartic entropy are represented by $n=2$, 3, and 4, respectively. The two continuity equations for the present model are found to be consistent with each other, especially when $n=2$, i.e., the Bekenstein entropy. The exchange of energy between the bulk (the universe) and the boundary (the horizon of the universe) should be a viable scenario consistent with the holographic principle.

The Savonius windmill, has been researched, developed, and tested for practical use for developing nations, a non-electric area and as temporary wind turbine power source. The structure of the windmill is very simple. Its efficiency is very high since it captures wind from all directions and at very low speeds. The Savonius system is a “micro wind power generator system"" and it has significant value statements. It is extremely portable. It is also easy to install and operate. During the testing phase, the Savonius system maintained stable power generation for nearly 10 years at less than 1 kW/h. The success of the Savonius testing phase has allowed the focus to shift to practical applications. The Savonius system consists of a windmill, a generator, a battery, and an electronic control circuit that includes effective security protocols. 1. The Rotor for SAVONIUS Wind Turbines The Savonius system is a windmill. It is cheap, efficient, and capable of processing continuous power. Its construction is simple and it poses little environmental hazard. The essential components of the windmill are paper, bamboo, and organic cloth. It is easily repairable and has a long operable lifespan. 2. The Generator In addition to the existing motors for home appliance, the magnetic circuits and control system are newly developed and are designed to provide maximum energy conversion and longevity in low efficiency conditions. 3. The Battery The system uses a low-cost lead storage battery power source. The windmill uses a nickel hydrogen system. Lithium ion batteries are also practicable. 4. Electronic Control circuit The generation of electricity adopts the latest electronic circuitry and loT technology. The goal is to maximize the system's durability. The circuitry optimizes the windmill's ability to generate power at wind speeds from slight breezes to wind storms. Experimental Study on the Effects of Relative Rotor Location to Duct Exit on Energy Recovery from Duct-Exhaust Flow Using a Butterfly Wind Turbine Makoto Kawanishi1, Yutaka Hara1, Katsuhiro Takagaki1, Takahiro Hara1, Kazuya Hori1 and Shigeo Yoshida2 1Tottori University, 2Kyushu University Abstract: Duct-flow power generation (DFPG) is an energy recovery method in which small wind turbines are used to generate electricity from the fluid energy flowing out of an exhaust duct. In the previous report, the validity of DFPG has been demonstrated by experiments and two-dimensional computational fluid dynamics. However, in those experiments to obtain the energy recovery rate, a wind turbine was located only on the centerline of exhaust flow. To investigate the effects of relative rotor location to duct exit on energy recovery, the similar experiments are conducted by installing a wind turbine away from the centerline of exhaust flow in this study. A Butterfly Wind Turbine (BWT), which is a vertical axis type with three looped blades, is used as the experimental rotor. The diameter is D=0.4m, height H=0.3m. A wind tunnel with the square nozzle of width W = 0.65m is utilized as an exhaust duct. The origin of a coordinate system is set at the center of the nozzle-exit. The BWT is positioned at one of 15 locations, which are designated by combination of the coordinate values of the mainstream direction X/D=1.25, 1.875, 2.5, 3.125, 3.75 and the lateral direction Y/W=-0.46, 0.0, 0.46. In each configuration, wind speed distribution on the nozzle-exit section (Y-Z plane at X = 0) is measured by using Pitot tube under the condition of constant base wind speed of 6 m/s. The maximum power coefficient of the wind turbine was Cp = 0.13, which was obtained in the case of rotor location of (X/D, Y/W) = (1.25, 0.46). The energy recovery rate η is defined as follows: (1) where PWT is the shaft power of the turbine, PKE0 is the fluid kinetic energy flowing out of the wind tunnel when a turbine does not exist, and ΔPKE is the loss of kinetic energy due to existence of the turbine. The maximum η was 2.7%, which was obtained when (X/D, Y/W) = (3.75, -0.46). The product ξ of the power coefficient Cp and the energy recovery rate η is defined as an indicator to evaluate the effectiveness of DFPG. Relatively great values of the indicator ξ were obtained when the turbine was installed at (X/D, Y/W) = (2.5, -0.46), (3.125, -0.46), and (3.75, -0.46). This shows that the turbine locations where a drag-type rotor works well might give better configurations for DFPG at downstream region.

It is a well-known fact that there are several possible convecting patterns for a given Rayleigh number, when a saturated porous square section is heated from below and cooled at the top, with adiabatic side boundaries. The question is which pattern among them is selected preferably or naturally by the system for a fixed value of the Rayleigh number. A pseudospectral numerical method was employed in order to investigate the problem. There are two important findings. One is that the convecting pattern carrying the greatest heat from the bottom to the top boundaries is more stable against disturbances than other possible patterns. This finding is consistent with the Constructal law, as well as the Maximum entropy production hypothesis proposed by Malkus. The other one is that once the system has selected a certain pattern, it persists despite the more heat carrying pattern exists, unless sufficient disturbances are introduced into the system. The system exhibits a strong initial value dependency.

This paper describes experimental results on the solidification process over the vertically positioned circular cylinder, placed in an aqueous solution of sodium nitrate, where the aqueous solution in the vessel is heated from the bottom. After the initiation of solidification by cooling the cylinder below the liquidus temperature, the pure ice formation on the cylinder causes the rejection of solute into the surrounding aqueous solution. The solute enriched vertical fluid layer over the ice then falls on the bottom of the vessel due to its higher density, and accumulates there. This process results in the formation of solute rich and hot horizontal layer (heavy layer), underlying the relatively cold but less concentrated fluid layer (light layer). As this process advances, however, because of the continuing influx of solute rich fluid, the lower heavy layer occupies more space, and the interface of the two layers rises slowly. The pH indicator method has been successfully employed in order to visualize the flows during this process. In this report, we document the evolution of both temperature and flow fields in the aqueous solution quantitatively, as the solidification progresses and the density discontinuity of the two layers rises.

The performance of the orthopter-type wind turbine in a shear flow was investigated. The orthopter-type wind turbine is one of the vertical-axis wind turbines (VAWT) which each blade combines a rotating movement around its own axis and a rotating movement around turbine's axis. The diameter and height of wind turbine were 510mm and 400mm, respectively. The number of flat plate blade was three. The experiments were carried out in an open circuit wind tunnel. The effects of the location of wind turbine and the strength of shear flow on the performances of the orthopter-type wind turbine were found. The power of the wind turbine increased when porous plate installed the backward side.

The flow around a rectangular cylinder which moves over a flat plate has been simulated by the LES method at Reynolds number of 7×10^3. The Smagorinsky model was used as a subgrid scale (SGS) model. The time-averaged and fluctuating fluid forces were calculated by changing the gap-to-height ratio S/H and the width-to-height ratio B/H of a cross section of the rectangular cylinder, as parameters. The lift force variations from the numerical analysis are good agreement with those of the experimental data from the towing water tank tests. It is found the relationship between the lift force variations to the gap-to-height ratio S/H and the flow pattern of three dimensional vortex structures.