Abstract This study entails an optimal airfoil-based curve section attached to a straight blade segment, forming a hybrid-bladed Savonius hydrokinetic turbine (HSHT) design. The aim is to investigate its detailed hydrodynamic performance under various design and flow conditions, common in low discharge channels. Three turbine types are conceptualized with different arc radii and aspect ratios. Initially, transient computational fluid dynamics (CFD) simulations are performed to investigate torque variation and compare their flow physics, which is followed by Taguchi optimization. Further, detailed CFD simulations have been carried out. The Taguchi optimized turbine design showcases five blade-fluid flow control-based interactions—(i) advancing blade's arc curvature flow control (both pressure and suction sides), (ii) overlapping and side gap flow control, (iii) curve edge gap flow control, (iv) Coanda-vector like flow control, and (v) vortical flow control, which make the optimal turbine design a better choice for pico-scale power generation. When the optimal curve profile (15 mm arc radius) and optimal aspect ratio (0.51) are used with water flow stream-speed 0.5 m/s, it exhibits a maximum Cp of 0.272 and CT of 0.68, respectively, for tip-speed ratio 0.7. Blade overlapping 20% and thickness 2 mm further enhance Cp and CT by 2.20% and 3.23%, respectively.

Abstract Systematic measuring of hydraulic machine's performance data at hydraulic model test rigs involves comprehensive expert knowledge of the test rig engineer and is time-consuming, as the multidimensional operation space must be explored manually. Expertise is needed to account for specific performance limits of test-rig equipment, model turbines, storage pumps, or pump turbines as well as some hysteresis of the setup due to flow separation and dealing with operation point-dependent gains between controlled parameters and measured quantities. To free valuable manpower from the burden of shift work, the measurement procedure is subject to automation. However, testing new automation concepts involves safety-critical or expensive tests and consumes valuable time at tests too. To develop and validate new automation concepts offline, we present a hybrid data-driven modeling approach to create a digital twin of the combined setup of a hydraulic turbine on a hydraulic test rig. Special attention paid to the modeling approach is consistent with existing mathematical relations governed by either physical models or norms. The presented approach allows the separation of test rig and hydraulic model machine under test and this enables offline validation of automation concepts on different combinations of test rigs and hydraulic model machines. The modeling approach is demonstrated by performing cross-validation using recorded measurement data.

Abstract The lattice Boltzmann method (LBM) is utilized to numerically investigate the permeability and effective thermal conductivity of simple cubic and body-centered truss structures. The key objective of this paper is to analyze how different geometric parameters affect the macroscopic properties of these truss structures that are increasingly used in advanced engineering applications due to their unique thermal-fluid characteristics. Simple cubic and body-centered cubic (SC-BCC) lattice structures are modeled, and the simulations are performed to determine their permeability and effective thermal conductivity. The findings highlight that the rod diameter and simple-cubic diameter significantly influence porosity, permeability, and thermal conductivity. Larger rod diameters generally result in higher porosity and permeability but may reduce thermal conductivity. Conversely, smaller simple-cubic diameters tend to enhance thermal conductivity. These results can optimize the design and application of truss structures in heat exchangers, cooling systems, and other areas where efficient thermal management and fluid flow are critical. The study concludes that LBM is an effective tool for predicting the thermal-fluid behavior of complex porous structures, providing valuable insights for the engineering design of advanced materials.

Abstract Ultra-high-speed centrifugal pumps are frequently utilized in chemical and aerospace industries, yet the impact of fluid weak compressibility on pressure pulsation remains unclear. This study employs the delayed detached eddy simulation (DDES) numerical method to investigate the effects of the medium's weak compressibility on the internal flow field structure of an ultrahigh-speed centrifugal pump, with a particular focus on pressure pulsations. The DDES numerical results were validated through experimental tests, showing good agreement with the experimental pump performance and measured pressure pulsation data, particularly at the blade passing frequency and under various flow conditions. Results indicate that under weak compressibility conditions, the density and velocity distribution of the fluid inside the pump are influenced. Moreover, the weak compressibility of the medium impacts the pressure pulsation signals under the design condition, especially for the monitoring points around the volute tongue where the amplitude is approximately 60∼85% of that in the incompressible state, besides, a significant impact under low flowrate is generated. By comparing the blade passing frequency–amplitude and the root-mean-square (RMS) energy within the 0-100 kHz frequency band, it is evident that considering weak compressibility effects results in overall lower pressure pulsation energy within the pump compared to the incompressible state. This finding suggests that the weak compressibility effect of the fluid has a suppressive influence on pressure pulsation in the ultrahigh-speed centrifugal pump.

Abstract This study is a continuation of the work of Lee et al. (2024, “Aerodynamics and Flowfield of Distributed Electric Propulsion Tiltwing During Transition With Deflected Trailing-Edge Flap,” ASME J. Fluids Eng., 146(5), p. 051202) in which a large increase in lift and decrease in drag of a semiwing equipped with four four-bladed propellers at Re = 2.26 × 105 were reported. The force-balance measurements however contained both the thrust generated by the distributed electric propulsion (DEP) wing and the propeller slipstream-produced lift and drag forces. In the present experiment, the propeller slipstream-produced lift and drag were calculated through the surface pressures developed on the tilt DEP wing at multiple spanwise locations. By subtracting the propeller slipstream-produced lift and drag from the direct force-balance data, the thrust force generated by the DEP wing at each tilt angle and propeller rotation was obtained. The DEP wing-produced thrust was found to agree well with the surface pressure and force-balance measurements. The behavior of the boundary-layer flow developed on the DEP wing was also analyzed through the surface pressure measurements. It is anticipated that the present study will further advance our understanding of the aerodynamics of tiltwing electrical vertical take-off and landing(eVTOL) during transition maneuvering and its design.

Abstract Floating offshore wind energy will play a key role in the clean energy transition. The number of large-scale wind farm projects is growing in regions like Northern Europe, the East Coast of the U.S., and the Mediterranean Sea. Offshore wind farms face fewer layout constraints, as they can be situated in vast, open sea areas. Turbines are often arranged in simple layouts, such as grid patterns, but this can cause significant annual energy production (AEP) losses due to wake–rotor interaction. Increasing spacing can mitigate this effect, but it may not always be feasible due to marine space limitations or higher costs for cabling and maintenance. This paper introduces a multi-objective wind farm optimization framework using a non sorted genetic algorithm (NSGA II) to minimize costs and maximize AEP. The method is applied to two case studies in the Mediterranean Sea, assuming 15 MW wind turbines. Case A is located off the coast of Civitavecchia, and case B in the Gulf of Squillace. AEP evaluation is performed with the open-source library FLOw Redirection and Induction in Steady-State (floris), while optimization is done using pymoo. In case A, the layout characterized by the lowest levelized cost of energy (LCOE) features 16 turbines, achieving an AEP of 709 GWh, an LCOE of 112.06 €/MWh, and wake losses of 2.6%. Meanwhile, in case B, the layout with the lowest LCOE consists of 19 turbines, achieving an AEP of 1140 GWh, an LCOE of 80.82 €/MWh, and wake losses of 4%.

Abstract The wall-modeled-large eddy simulation (WMLES) technique was used to analyze turbulent flow in a porous medium composed of a staggered arrangement of square cylinders. The study focused on a porosity range of 0.3–0.8 at a pore Reynolds number of 104. The research provides novel information on pressure and shear force distributions around the cylinders and time-averaged values of particle drag and fluctuating lift coefficients. Results indicate that flow physics are mainly driven by an expansion region in front of the central particle and another one in the rear, where the flow is contracted and strongly accelerated. In the first region, velocities, turbulence kinetic energy (k), and its dissipation rate (ε) are attenuated by a sudden pressure increase, while in the contraction region, the effect is the opposite. As porosity decreases, flow gradients and the overall levels of k, ε, and normalized Reynolds stresses become more significant. Turbulent anisotropy increases as porosity decreases below 0.6. Hydrodynamic stresses in the last interval present relatively uniform levels, which is a unique feature that may be considered in designing dedicated engineering devices with controlled stresses.

Abstract In this work, the heat transfer in double pipe heat exchangers (DPHEs) with small tube spacing is analyzed. This type of heat transfer is generally described in many literary sources; however, in laminar flow, the resulting values of the theoretical equations differ. Moreover, the small spacing of the pipes can affect the fluid flow and subsequent heat transfer. The suitability of using available theoretical methods for the design of double pipe heat exchangers (the Stephan, VDI, and Baehr methods) was evaluated. A series of experiments was carried out on a double pipe heat exchanger with a tube spacing of 1.4 mm. The experimentally determined value of the heat transfer coefficient (HTC) was up to two times higher in comparison with the values calculated according to theoretical methods. The relative increase was more significant for the lower Reynolds number values. At the same time, the difference of the wall temperature along the circumference of the outer tube was detected. This phenomenon was theoretically analyzed and can be explained by tube misalignment in the small tube spacing. The procedure of quantification of this effect was proposed. This effect may cause an inhomogeneity of the media flow and temperature distribution and, as a result, increase the performance of the heat exchanger by tens of percent.