This paper proposes a new acceleration gradient method by addition of the Taylor expansion and conjugate direction to Nesterov’s acceleration gradient method. It was validated by updating the oil film thickness to minimize the friction coefficient on a textured surface. Nesterov’s acceleration gradient method converges faster than the gradient method for classical first-order optimization methods. The Taylor expansion of this mathematical technique reaches a more accurate approximation by incorporating higher-order terms. The conjugate direction is used in large-scale problems because it offers better convergence than the gradient descent method and is less memory-intensive than the Newton method. We introduced these into Nesterov’s acceleration gradient method to improve the convergence rate. The gradient of the design variable was obtained by the adjoint variable method. The results demonstrate the proposed method to converge faster than Nesterov’s accelerated gradient method. All the numerical calculations were performed by the finite element method using FreeFEM++.

This study provides detailed information on the pressure distribution inside a pipe with a continuous longitudinal slot, theoretically investigating the parameter dependency of the pressure distribution on the design parameters of the pipe: Reynolds number at the inlet, aspect ratio of the pipe, slot width, and pressure loss coefficient of the slot. The flow through a pipe with a continuous longitudinal slot is theoretically modeled in one dimension. The model follows the mass and energy conservation laws and considers the pressure loss at the slot. The results show that depending on the aspect ratio of the pipe and the Reynolds number at the inlet, the pressure distribution inside the pipe is categorized into three regimes: monotonically increasing, monotonically decreasing, and downward concave profiles. A parametric study indicates that a monotonically decreasing profile appears for a high aspect ratio pipe. A lower aspect ratio pipe, on the other hand, has a monotonically increasing pressure profile. The present paper also reports the effects of the slot width and pressure loss coefficients on the pressure distribution, indicating that the regime of the pressure distribution is mathematically predictable using the function of the design parameters.

The effects of cross flow and fluctuating cross flow on the aerodynamic performance of multirotor drone propellers were investigated by using wind tunnel testing and numerical simulations. Three hovering propellers were examined and were designed based on Adkins and Liebeck theory with modifications. Thrust coefficient C_T and power coefficient C_P of each propeller were experimentally measured and Figure of Merit FM was evaluated. From the cross flow experiments and numerical simulations, C_T, C_P and FM calculated were in reasonable agreement with the experimental results at high cross flow velocity. The results implicated that a stall might occur at near the root of the propeller as well as demonstrated that the starting point of the propeller design played a role in aerodynamic performance under the cross flow conditions. Moreover, from the fluctuating cross flow experiments, C_T, C_P and FM fluctuated in time and the propellers are more susceptible to cross flow and fluctuating cross flow at lower rotational speed in terms of the amount of change of aerodynamic forces.

A potential way to reduce the noise generated by construction machinery cooling systems is to satisfy the flow rate required for cooling at lower fan speeds, and a promising approach to achieving this goal involves finding ways to reduce the pressure drop that occurs in the cooling system ventilation passages. Towards that end, approaches using computational fluid dynamics (CFD) have proven effective for estimating three-dimensional (3D) spatial pressure drops, but there have been few reports on actual loss mechanisms. In this study, the mechanisms of pressure drops that occur inside a cooling system enclosure and around exhaust port vents were investigated by capturing the flow discharged by the axial fan within the enclosure into the atmosphere via the exhaust port. We found that portions of the fan outlet flow divert significantly inside the enclosure and are exhausted at exhaust port outlets located some distance away from the fan. We also found that the pressure drops in such locations are larger than experienced by flow discharged via the shortest path. Since flows within the enclosure collide with each other and become unsettled around the exhaust port, turbulent kinetic energy increases, thus intensifying the pressure drop. Hence, by expelling the flow at the exhaust port via the shortest path without allowing it to mix chaotically inside the enclosure, the flow rate can be increased using the same fan speed.

We investigate the sensitivity to the application range of buoyancy force near the boundary in the diffuse-interface immersed boundary method. The flow fields not only inside the boundary but also outside the boundary are usually computed in the immersed boundary method. From a physical point of view, the buoyancy force should be zero inside the boundary and applied only outside the boundary. In addition, in diffuse-interface methods, the boundary is expressed by the volume force distributed near the boundary, i.e., there is an ambiguity in distinguishing the inside and outside of the boundary. In the present study, we define the application range of buoyancy force by using a weighting function which smoothly varies from 0 to 1 with a small thickness ξ, which expresses the ambiguity of the boundary. In order to investigate the effect of the application range of buoyancy force, we simulate the sedimentation of a cold circular cylinder in a heated channel, where the buoyancy force has a significant effect on the flow and temperature fields and the cylinder motion, for various values of ξ. As a result, we find that the results are very sensitive to the application range, and the movement pattern of the cylinder significantly varies depending on the value of ξ, even when it is less than one lattice spacing. Since each of the results with different values of ξ is supported by different existing studies, an appropriate value of ξ is unclear. These results pose a problem on an appropriate application range of buoyancy force in the diffuse-interface method, which has been overlooked.