Abstract Stability studies were conducted on a single-stage, low-speed compressor with different rotor loading-distribution designs under a uniform inlet, 10% intensity, and 20% intensity total tip pressure distortion inlet conditions via numerical calculations, theoretical model predictions, and experimental methods. The steady numerical performance was in basic agreement with experimentally measured performance. The theoretical prediction model showed an error within 1.5%, which is less than that of the steady numerical calculation. The total tip pressure distortion reduced flow stability. Conversely, the design of moving the rotor loading axially rearward significantly improved the flow stability. The blade loading analysis showed that the radial distortion caused a radial redistribution of rotor loading. The increase in the rotor-tip loading due to tip distortion was the main reason for the reduced flow stability. In contrast, the design of moving the rotor loading axially rearward reduced the rotor-tip leading-edge loading, enhancing the flow stability. Moreover, an analysis of the unsteady flow validated the findings of the blade loading analyses. It was found that the periodic evolution of the tip leakage vortex (TLV) had an adverse effect on flow stability. In addition, the modified rotors could prevent the tip leakage flow (TLF) from spilling from the leading edge and prevent the interaction of different diffusing regions, decreasing the probability of flow separation.

The correct affiliation for Syed Ahmad Raza is:Department of Mechanical Engineering, NED University of Engineering & Technology, Karachi 124087, PakistanThe correct affiliation for Ming-Jyh Chern is:Department of Mechanical Engineering, National Taiwan University of Science and Technology, Taipei 106335, Taiwan

Abstract Hydraulic axial turbines are more frequently utilized for grid regulation purposes. Sometimes, they must be operated at speed-no-load (SNL) conditions, which is characterized for some machines by a varying number of large vortical flow structures extending from the vaneless space to the draft tube, introducing detrimental pressure pulsations throughout the turbine. A recent study shows that the vortices can be mitigated by individually controlling the guide vanes. Since optimization of the distributor layout is linked with a large degree-of-freedom, machine learning is deployed to assist in finding an optimal setup cost-effectively. A reduced numerical computational-fluid-dynamics (CFD) model is built and used to generate input for Gaussian process regression surrogate models by performing 2000 steady-state simulations with varying distributor layouts. The surrogate models suggest that the optimal layout is to open seven out of 20 guide vanes in succession while keeping the remaining ones closed. However, this configuration induces large radial forces on the runner, and after implementing some modifications by trial and error, detailed time-dependent CFD simulations show that placing 4 + 3 opened guide vanes on opposite sides of the runner axis is better; it reduces the pressure peaks corresponding to a two- and three-vortex configuration, and the maximal pressure pulsations by as much as 88% in the vaneless space compared to regular SNL operation. Meanwhile, the radial force on the runner is reduced by more than 83%, and pressure pulsations on the runner blades by more than 55%, compared to the surrogate models' optimal layout prediction.

Abstract A unified one-dimensional (1D), steady-state flow and heat transfer model is presented for the pipeline transport of fluids at high pressures, including the supercritical (SC) conditions. The model includes a generalized temperature equation, presented here for the first time, and accounts for all of the important effects, including the property variation, viscous dissipation, Joule-Thomson (J-T) cooling, and heat exchange with the surrounding. With appropriate approximations, this model can yield all isothermal and nonisothermal pipe flow solutions reported thus far. A generalized multizone integral method is developed which solves the two resulting algebraic equations for pressure and temperature in conjunction with a property database, such as the National Institute of Standard and Technology (NIST) reference fluid thermodynamic and transport properties (REFPROP). With appropriately selected number and size of the zones and using property values at the mean temperature and pressure within each zone, this integral method can accurately predict the complex effects of the governing parameters, such as the pipe diameter and length, inlet and exit pressures, mass flowrate, J-T cooling, and inlet and surrounding temperatures. Its accuracy for small-to-large diameter pipes has been ascertained by a comparison with the numerical solutions of the differential form of governing equations that requires a large number of small grids along the pipe and the values of mean properties within each grid. Indeed, this integral model can be used for the pipeline transport at both subcritical and supercritical pressures as long as the fluid does not encounter its anomalous states and the phase-change.

Abstract The effect of tires on the overall aerodynamic drag in a car–tire assembly has been studied and deemed considerable from past studies. It has been shown that it is important to understand how the vehicle body and the tires influence the flow structures generated. Previous studies focused on the tire attributes that have an impact on the aerodynamic performance of the vehicle. These tire attributes, however, have not been studied extensively. This paper studies the impact that specific tire attributes have on the overall aerodynamic drag on the vehicle through a systematic sensitivity study. In this study, the DrivAer model is used due to the extensive research that has been done on the model. A baseline computational fluid dynamics model of the tire–vehicle assembly of the DrivAer model is simulated using ansysfluent in the open road domain to understand the flow structures around the body of the vehicle. Simulations are done on the fastback configuration of the DrivAer model with a smooth underbody. Coefficient of drag and coefficient of pressure results from the simulation are validated from experimental data. Data from the simulations and design of experiments are used to quantitatively compare the drag contribution of different parameters of the tire. The sensitivity analysis of the tire–vehicle assembly model performed gives a better insight into the modeling techniques that can be used on a car–tire assembly, as well as the impact of the parameters that could be selected for future tire model optimization.

This corrigendum is regarding the discussion and suggestions by Professor Dr. Asterios Pantokratoras on the paper “Some Exact Analytical Solutions for Two-Dimensional Flow of an Incompressible Second Grade Fluid (2015, ASME J. Fluids Eng., 137(10), p. 101206),” to whom we like to share our appreciation. In the subsequent sections, we present the corrections made in accordance with his comments and suggestions. In the original published paper [1], the results in Secs. 3.3 and 3.4 are erroneous. In this corrigendum, we present correct solutions for cases in Secs. 3.3 and 3.4.This is the case of the classical Newtonian fluid, and in this case Eq. (19) is rewritten as [1] (1)X′ Y(3)−X(3) Y′+ν X(4)+ν Y(4)=0where ν=μ/ρ [m2s−1].This is the case of non-Newtonian second grade fluid, and in this case Eq. (19) is rewritten as [1] (12)−X(3) Y′+X′ Y(3)+ν (X(4)+Y(4))+α (X(5)Y′−X′ Y(5))=0where ν=μ/ρ [m2s−1] and α=α1/ρ [m2].The exact solution here is completely similar to Eq. (11), actually no new solution has been found. The author is thankful to Professor Dr. Francine Battaglia (Editor-in-Chief), Professor Dr. Asterios Pantokratoras, and the reviewer of the “Discussion” for their constructive comments and valuable suggestions.The authors attest that all data for this study are included in the paper.

Abstract Despite the observation of change in the cavitation regime on a heated surface, the specific section of the wall surface that plays a more dominant role in this transition phenomenon remains unknown. This study experimentally investigated the effect of surface temperature of different regions on the cavitating flow in terms of the cavitation regime. The experiments were conducted using a convergent-divergent Venturi nozzle comprising two parts that could be heated independently. The Venturi nozzle could be fully or selectively heated at either the front, where the leading edge of the cavity sheet was located, or the rear, where the cavity sheet developed. The cavitation behavior under different heating conditions was investigated using high-speed visualization and fluctuating pressure measurements. Compared with the non-heated case, which exhibited a sheet-cloud cavitation regime, the cavitation regime on the completely heated Venturi nozzle exhibited transient cavitation. The same transition phenomenon was observed when only the front of the Venturi nozzle was heated. A liquid film was observed beneath the cavity sheet of transient cavitation when only the front portion was heated. In contrast, heating the rear part alone did not induce a change in the cavitation regime. Thus, it appeared that the transition of the cavitation regime on a heated surface was mainly influenced by the temperature increase at the leading edge of the cavity sheet.

Abstract Analysis on eddy motion is the essential method for understanding viscous flows. Compared with the current methods to identify the vortex, the study presents a method to investigate vortex structures based on topological analysis and nonlinear dynamics, and establishes a connection between the direction of the vortex and the real eigenvalue of the velocity gradient tensor. The study highlights the significance of the real and imaginary parts of complex eigenvalues in vortex development, wherein the real part indicates topological stability and the imaginary part represents swirling strength, contributing to get the characters of the viscous flows.

The ASME Journal of Fluids Engineering (JFE) and the ASME Fluids Engineering Division (FED) present a special issue of papers that were presented at the 2023 ASME-JSME-KSME Fluids Engineering Division Summer Meeting (AJKFluids 2023). The first FED joint meeting of the mechanical engineering societies between the United States, Japan, and Korea was in 2011. The 2023 FED conference marks the second year with Japan as the host country. The conference cochairs were Dr. Takeo Kajishima (Osaka University) and Dr. Genta Kawahara (Osaka University) representing JSME, Dr. Kamran Siddiqui (University of Western Ontario) and Dr. Marianne Francois (Los Alamos National Laboratory) representing ASME, and Dr. Han Seo Ko (Sungkyunkwan University) and Dr. Gwang Hoon Rhee (University of Seoul) representing KSME.The AJKFluids 2023 conference was held in Osaka, Japan, from July 9–13, 2023, at the Osaka International Convention Center. The special issue dedicated to this conference includes 12 papers invited based on their conference presentations and extended abstracts. The collection of topics includes both experimental and numerical studies on multiphase flow, turbomachinery, turbulent fluid motion, and applications with additive manufacturing. I am grateful for the assistance of the FED executive committee members who helped review the extended abstracts and select the paper contributions. Special thanks to Professor Philipp Epple, Dr. Marianne Francois, and Professor Ning Zhang.The Special Issue also presents the winners of the Flow Visualization competition, organized by Professor Philipp Epple. The 2023 winners in the video category were as follows:In closing, my sincerest gratitude is extended to our colleagues who served as reviewers, and of course the authors, whose contributions comprise the special issue. I would also like to acknowledge the JFE guest editors, Dr. Xiang Yang and Dr. Deify Law, who shared in the responsibilities to support the special issue. We are indebted to the JFE editorial assistant, Ms. Colette Montague, who helped ensure timely processing, and the support of the ASME staff, especially Ms. Beth Darchi, Ms. Erica Hodge, and Ms. Tamiko Fung.

Abstract The design and optimization of propellers for unmanned aerial vehicles (UAVs) are essential for optimal performance and high efficiency. This study presents a numerical investigation of the aerodynamic performance of coaxial octocopters using openfoam as flow solver. While the aerodynamic performance is affected by many parameters, the current study focuses on four main parameters: the propeller type, the horizontal and vertical separation distances between the propellers, and the ratio between the rotational speeds of the upper propeller and the lower one. To find the minimum number of simulations to be performed within defined limits, and reduce the number of computational fluid dynamics (CFD) simulations that cause high computational cost, Taguchi method was employed. In this study, average thrusts were calculated for the preliminary design of the octocopter by examining an isolated single propeller and dual- and quad propellers taking their rotation directions into account. The Taguchi design matrix revealed that for all cases investigated, the propeller type is the most dominant design parameter followed by the velocity ratio of the upper propeller to the lower one (nU/nL) and vertical (z/D) and horizontal (ℓ/D) orientation of coaxial propellers. However, it was shown that ℓ/D and z/D may play a significant role in vortex formation and pressure fluctuations which should be considered as design criteria for coaxial octocopters associated with flow attributes. The results showed that the aerodynamic performance parameters are not dependent on all the selected parameters, and demonstrated that the selected propeller designs improved aerodynamic performance.