Three-dimensional Numerical Simulation Data Research Articles

Thermal-hydraulic performance and optimization of attack angle of delta winglets in plain and wavy finned-tube heat exchangers

This work is related to numerical investigation and optimization of the attack angle of delta winglet type vortex generators in plain and wavy finned-tube heat exchangers. For this purpose, three-dimensional numerical simulation data and a multi-objective genetic algorithm with Artificial neural network are employed. The heat exchanger models considered in this study are three rows of tubes in staggered arrangement. The angle of attack (α) of delta winglets and Reynolds number varies from 15° to 75° and 500 to 1300, respectively. Results are illustrated by investigating the flow structures and local heat transfer coefficient. Results show that compared to plain fins, wavy fins enhance the heat transfer performance of the heat exchanger due to constant disruption of thermal boundary. Applying delta winglets on the plain and wavy fins further increased the heat transfer by energizing flow in the wake of tubes while friction factor is also increased. To achieve a maximum heat transfer enhancement and a minimum pressure drop, the optimal angle of attack for varying Reynolds numbers are calculated using the Pareto optimal strategy. For this purpose, CFD data, artificial neural network and a multi-objective genetic algorithm are combined. Results show that compared to the corresponding smooth fins, heat transfer per unit volume (Qv) and pumping power per unit volume (Pv) performances of delta winglets in wavy finned-tube heat exchanger has increased up to 12.5% and 7.41%, respectively. Similarly, for plain finned-tube heat exchangers, the maximum increase in Qv is 14.7% while Pv is increased by 6.93%.

洪水時のADCPデータに基づく更正係数の分布特性と流量推定の高度化に関する研究

In estimating river flow discharges from water surface velocity distributions measured by non-contact methods such as radio wave velocity meters or image-based techniques, it is important to use an appropriate value of surface velocity coefficient that yields a depth-averaged velocity from a surface velocity. Conventionally, a value of 0.85 has been widely used in practical purposes but its distribution feature under various conditions has not been clarified yet. In order to investigate a fundamental aspect of the coefficient, measurement data by a tethered ADCP, a remote-controlled ADCP and surface velocities obtained by space-time image velocimetry(STIV) as well as a three-dimensional numerical simulation data were compared for the floods of the Uono River and the Niyodo River. It was made clear from measured and numerical data that the variance of the coefficient distribution tends to increase with decrease of the relative water depth and vice versa.

Radiative Aerothermodynamics of Entering Space Vehicles: Toward the Use of State-to-State Approach

Modern problems of radiative aerothermodynamics of entering space vehicles are demonstrated and analyzed in the paper. New radiative gas dynamic problems concerned to coupling processes of non-equilibrium dissociation with radiation heat transfer in shock layers generated above large scale re-entry space vehicles returning from orbital and super orbital space mission are considered in the first part. Three-dimensional numerical simulation data on radiative aerothermodynamics of Martian entry probes Pathfinder, Exomars and Mars Science Laboratory (MSL) are presented and analyzed in the second part. It is shown that integral radiative heating of leeward surface of the entry probes exceeds corresponding convective heating. The third part is dedicated to consideration preliminary numerical simulation results on radiative gas dynamics of Galileo probes. At first, a review of the available results obtained during the mission preparation and post-flight analyses has been undertaken to select a computational matrix. This matrix has been selected by accounting for previous numerical efforts from the literature to crosscheck the results. Then, a model based on previous efforts has been set up for computing the flow-field around the probe at high altitude. Finally the test case matrix has been computed and crosschecked with existing numerical predictions performed. Some possibilities of innovative magneto-hydrodynamic (MHD) technologies being applied to solve problems of re-entry vehicles heat protection are discussed in the fourth part. All presented data demonstrate necessity of further development of the radiative aerothermodynamics based on state-to- state approaches.