Search Results (26)

The present work aims to propose a new calibration strategy of the Hall–Thollet Body Force (BF) model to simulate the flow in multi-stage compressors and to capture inlet distortion effects within the machine. Both global (0D) and radial (1D) correction terms are introduced and calibrated to improve predictions in multi-stage compressors, accounting for highly interacting, highly loaded blades, falling outside the validity range of the model’s original coefficients. The modified model has been tested on the 3.5-stage high-pressure compressor CREATE, for which experimental data are available. The modified model is then employed to study different patterns of inlet distortion. The results show a very good agreement between Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations and Body Force calculations in terms of performance, key quantities along the radial and circumferential directions and distortion transfer across the compressor. Full article

Improved ship design and market demands have driven the adoption of multi-propeller systems for propulsion in recent years. This study examines the hydrodynamic performance of two KP505 propellers arranged in various transverse and longitudinal spacings, utilizing an in-house CFD code. The numerical simulations employ the URANS method with the SST k-ω turbulence model and a structured overset grid approach. First, standardized mesh and time-step convergence studies are conducted following ITTC recommendations. The hydrodynamic results for the KP505 propeller are compared with experimental data to validate the reliability of the method. Subsequently, over 40 propeller arrangements with varying transverse and longitudinal spacing are simulated. Thrust, torque, and efficiency under different operating conditions are calculated, and key flow field data are analyzed. Finally, the interference characteristics between propellers at different positions are examined by comparing the results with those of a single KP505 propeller. The findings indicate that the high-speed wake generated by the upstream propeller significantly affects the hydrodynamic performance of the downstream propeller. This interaction diminishes as the transverse spacing between the propellers increases. To ensure the propulsion efficiency of the two-propeller configuration, the transverse spacing should not be less than one times the diameter of the propeller. Full article

The aerodynamic performance of transonic compressors, particularly the stall margin, is significantly influenced by inlet distortion. While time-marching methods accurately simulate such unsteady flows, they can be time-consuming. To enhance the computational efficiency, two Fourier-based methods are proposed in this paper: the time-accurate method with interface filtering and the time–space collocation (TSC) method. The time-accurate method with interface filtering ignores the rotor–stator interaction effects, enabling a larger time step and faster convergence. In contrast, the TSC method accounts for harmonics of conservative variables and transforms the unsteady simulation into multiple steady-state calculations, thereby reducing computational costs. The two Fourier-based methods are validated using NASA Stage 67 and a two-stage transonic fan. Near the peak efficiency point, the results from both methods closely match that of URANS simulation and experimental data. The time-accurate method with interface filtering demonstrates a speed enhancement of 4 to 5 times as a result of a reduction in the iteration steps. In contrast, the TSC method exhibits a speed improvement of at least 20 times in two specific cases, attributable to the significantly smaller mesh size and iteration steps employed in the TSC method compared to the URANS method. Near the stall point, more harmonics for inlet distortion are necessary in TSC simulation to accurately capture flow separation. In the two-stage transonic fan simulations, the strong rotor–stator interaction effects lead to deviations from the URANS simulation; nevertheless, the Fourier-based simulations accurately reflect the trend of the stall margin under total pressure distortion. Overall, the Fourier-based methods show promising potential for engineering applications in estimating the performance degradation of compressors subjected to inlet distortion. Full article

This paper presents the results of a study of self-sustained processes excited in a Helmholtz resonator after a flow over its orifice. A comparative analysis of various approaches to the numerical modeling of this problem was carried out, taking into account both the requirements for achieving the required accuracy and taking into account the resource greediness of calculations, the results of which were verified by comparison with data obtained during a special experiment. The configuration with a spherical resonator with a natural frequency of 260 Hz and an orifice diameter (about 5 cm) in an air flow with a speed of 6 to 14 m/s was considered. A comparison of the calculation results with data obtained in experiments carried out in the wind tunnel demonstrated that the accuracy of calculations of the characteristics of the self-sustained mode using the simplest URANS class model tends to the accuracy of calculations within the large eddy simulation approach formulated in the WMLES model. At the same time, when using WMLES, it is possible to better reproduce the background level of pulsations. From the point of view of resource greediness, expressed in the number of core hours spent obtaining a solution, both models of the turbulence turned out to be almost equivalent when using the same grid models. Full article

Unsteady separation is a phenomenon that occurs in many flows and results in increased drag, decreased lift, noise emission, and loss of efficiency or failure in flow devices. Turbulence models for the steady or unsteady Reynolds-averaged Navier–Stokes equations (RANS and URANS, respectively) are commonly used in industry; however, their performance is often unsatisfactory. The comparison of RANS results with experimental data does not clearly isolate the modeling errors, since differences with the data may be due to a combination of modeling and numerical errors, and also to possible differences in the boundary conditions. In the present study, we use high-fidelity large-eddy simulation (LES) results to carry out a consistent evaluation of the turbulence models. By using the same numerical scheme and boundary conditions as the LES, and a grid on which grid convergence was achieved, we can isolate modeling errors. The calculations (both LES and RANS) are carried out using a well-validated, second-order-accurate code. Separation is generated by imposing a freestream velocity distribution, that is modulated in time. We examined three frequencies (a rapid, flutter-like oscillation, an intermediate one in which the forcing and the flow have the same timescales, and a quasi-steady one). We also considered three different pressure distributions, one with alternating favorable and adverse pressure gradients (FPGs and APGs, respectively), one oscillating between an APG and a zero-pressure gradient (ZPG), and one with an oscillating APG. All turbulence models capture the general features of this complex unsteady flow as well or better than in similar steady cases. The presence, during the cycle, of times in which the freestream pressure-gradient is close to zero affects significantly the model performance. Comparing our results with those in the literature indicates that numerical errors due to the type of discretization and the grid resolution are as significant as those due to the turbulence model. Full article

Regular and irregular waves were numerically generated in a wave canal to investigate hydrodynamic loads acting on a wind turbine monopile and to predict its structural response. The monopile was implemented in the canal and modeled as a flexible structure, with the turbine blades and rotors considered as a point mass situated at the top of the monopile. Fluid–structure interaction (FSI) simulations were performed by coupling a structure solver based on a finite element method (FEM) with an unsteady Reynolds-averaged Navier–Stokes (URANS) equations solver of the finite volume method (FVM). The FSI simulations considered the two-way interaction between the deformable structure and the fluid flow. The URANS equations solver was coupled with the volume of fluid (VoF) method to account for the two-phase flow. In regular waves, numerically predicted total load coefficients occurring at the monopile’s first eigenfrequency compared favorably to experimental measurements. A deviation between calculations and measurements was observed for the total loads in irregular waves. This deviation occurred due to the smaller wave energy density of the numerically predicted irregular wave. Hydroelasticity effects increased wave-induced forces by about 6% and wave induced bending moments by about 16% in regular waves. A relatively strong whipping event was observed, which characterized the hydroelasticity response bending moment of the monopile in irregular long-crested waves. This whipping event also had a significant influence on the loads on the monopile. These investigations demonstrated the favorable use of FSI simulations to predict hydroelasticity effects on a monopile. Full article

This paper presents a first investigation into the aerodynamics and performance breakdown of a distributed aft-fuselage boundary layer ingesting (BLI) tube-and-wing aircraft using fully coupled Unsteady Reynolds-Averaged Navier-Stokes (URANS) calculations that resolve the complete fan and installation geometries. Through the URANS simulations, the interaction between the turbulence from the fuselage boundary layer (BL) and the BLI propulsor is identified as an area that warrants further research. Using the URANS approach, the ingested turbulence leads to a 4.5% reduction in the propulsor stage total–total isentropic efficiency. A mechanical power balance has been drawn up to compare the power sources and sinks throughout the installation and propulsor for two test cases with different thicknesses of ingested BL. The test case with a thinner BL was found to generate significantly more dissipation in the BL development upstream of the propulsor, the flow separation over the outer cowl, and the interaction between the reversed flow over the cowl and the propulsor exhaust jet. Due to this increase in dissipation, the case with thinner ingested BL consumes 7% more power relative to a baseline case with thicker BL, representative of the upstream fuselage at cruise. This demonstrates the importance of matching the installation with the incoming fuselage BL. Full article

The consideration of shallow water effects has gained in importance regarding inland operations. The interaction between the keel and the riverbed affects the hydrodynamic characteristics of marine vessels. The highly complex nature of the interference phenomenon in catamarans makes the shallow water problem more complicated as compared to monohulls. Hence, catamarans are very sensitive to speed changes, as well as to other parameters, such as the shallow water effects. This makes the design of catamarans more challenging than their monohull equivalents. At lower Froude numbers, the higher importance of the frictional resistance makes the greater wetted surface of the catamaran a disadvantage. However, at higher speeds, there is the potential to turn their twin hulls into an advantage. This study aims to investigate the wave-making resistance of a zero-carbon fast passenger ferry operating in shallow water. The URANS (unsteady Reynolds-averaged Navier–Stokes) method was employed for resistance simulations. Then, the double-body approach was followed to decompose the residual resistance into viscous pressure and wave-making resistance with the help of the form factors of the vessel calculated at each speed. The characteristics of the separated wave-making resistance components were obtained, covering low, medium, and high speeds. Significant findings have been reported that contribute to the field by providing insight into the resistance components of a fast catamaran operating in shallow waters. Full article

The geometry of a conventional two-bladed Savonius rotor was used in this study based on a report available in the literature. A two-dimensional rotor model consisting of two buckets and an overlap ratio of 0.1 was prepared. The unsteady Reynolds averaged Navier-Stokes (URANS) equations and the eddy-viscosity turbulence model SST k-ω were employed in order to solve the fluid motion equations numerically. Instantaneous velocities and pressures were calculated at defined points around the rotor and then averaged. The research shows that the operating rotor significantly modifies the flow on the downwind part of the rotor and in the wake, but the impact of the tip speed ratio on the average velocity distribution is small. This parameter has a much greater influence on the characteristics of the aerodynamic moment and the distribution of static pressure in the wake. In the upwind part of the rotor, the average velocity parallel to the direction of undisturbed flow is 29% lower than in the downwind part. Full article

The purpose of this study is to consider propeller geometry and blade rotation in the propeller model in a CFD code. To predict propeller performance, a body force propeller model was developed based on blade element theory and coupled with URANS (unsteady Reynolds-averaged Navier–Stokes) solver CFDSHIP-IOWA V4.5 both implicitly and interactively. The model was executed inside the flow solver every inner iteration. The grid points inside each 2D blade geometry were identified by a numerical search algorithm. To calculate the lift coefficient, the total flow velocities at 25% foil chord length were obtained using the inverse distance weighting interpolation from the RANS solution. The body forces were distributed linearly along the chord length with the maximal value located at the leading edge and zero at the trailing edge. The main achievements are: (1) for a KP505 propeller in an open water condition, the error of the thrust coefficient generally is around or less than 3%, which is a better prediction than the previous model. (2) For a behind-hull condition, the error is about 1%. (3) For an E1619 propeller in an open water condition, the error is around 6%. (4) The blade-to-blade effect and unsteady flow field between blades are sufficiently resolved by the model. Full article

So as to improve the reliability and accuracy of marine simulators, it is essential to predict ship heave and pitch motions in regular waves. The motions of two ships, the international standard model KVLCC2 and the first training ship, “Yukun”, of Dalian Maritime University, are simulated using a three-dimensional (3D) numerical wave tank based on the Unsteady Reynolds Averaged Navier–Stokes (URANS) equations. The free surface is captured by the volume of fluid (VOF) method, and an SST k-ω turbulence model is used to describe the turbulence flow. The numerical model is first validated for the standard KVLCC2 at three different speeds through a comparison with the published experimental data and the potential flow results. Then, numerical simulation is performed for the motion of the ship Yukun with different speeds under various sea conditions. The heave amplitude of the hull changes with the increase in the wavelength when the maximum value is reached. Upon comparing the RAOs of ship motions under different wave steepness conditions, it is apparent that the heave and pitch motions of ships nonlinearly decrease with an increase in wave steepness. The results were added to the database of the marine simulator to further improve the accuracy and realism of the simulator. Full article

High-speed vehicles traveling in a tube with pressures similar to those experienced by aircraft at their maximum altitude are presented. Although the concept resembles Hyperloop, the pressure level investigated here is much higher and safer than that suggested by Hyperloop, and, therefore, the system design is markedly different. Calculating a vehicle’s aerodynamic performance in the initial design stages requires low-budget computational tools to enable iterative design processes. This study presents an algorithm for rapid flow-field prediction based on a one-dimensional Reimann solution, including viscosity and heat transfer effects. The flow-field is divided into near- and far-fields, where the near-field represents the solution directly around the vehicle. The far-field demonstrates the impact of the vehicle’s motion on the vehicle’s flow-field upstream and downstream. Two-dimensional URANS models are compared to the current numerical scheme. The developed algorithm analyzes the flow-field and the propagation of pressure waves along the tube to simulate the vehicle’s movement. The one-dimensional model shows the robustness and predictability of the near and far flow-fields. The results from the developed scheme provide good agreement, with less than a few percent deviations, compared to CFD simulations but with significantly lower computational resources. Full article

The applicability of the solution of the unsteady Reynolds-averaged Navier–Stokes equations (URANS) for the numerical simulation of the periodic quasi-switching regime of vortex generation and heat transfer in a deep conical dimple with a slope angle of ${10}^{\circ }$ on the wall of a narrow channel is substantiated. To calculate the turbulent regime, the model of shear stress transfer by Menter 2003, modified taking into account the influence of the curvature of streamlines within the framework of the Rodi-Leshziner-Isaev approach, is used. At Reynolds number $Re={10}^4$, the oscillation period of the transverse $R_z$ and longitudinal forces $R_x$, as well as the total heat transfer $N{u}_{mm}$ to the control section of the heated channel wall with a dimple, is set equal to 60, which corresponds to the Strouhal number $St=0.0167$. Computer visualization of swirling jet-vortex flows demonstrates focus-type sources on the side faces of the dimple. In the self-oscillating mode, a two-cell vortex system is formed with different intensities at the oscillation period $R_z$. Periodic changes in friction, Nusselt numbers and temperature are recorded in the longitudinal and transverse median sections of the dimple and reflect the oscillations of the vortex structure from left to right and from right to left. The formation of a fan jet is shown, which oscillates relative to the plane of longitudinal symmetry, causing a redistribution of power and thermal loads. Full article

The design and development of a small molecule named NPB [3-{(4(2,3-dichlorophenyl)piperazin-1-yl}{2-hydroxyphenyl)methyl}-N-cyclopentylbenzamide], which specifically inhibited the phosphorylation of BAD at Ser99 in human carcinoma cells has been previously reported. Herein, the synthesis, characterization, and effect on cancer cell viability of NPB analogs, and the single-crystal X-ray crystallographic studies of an example compound (4r), which was grown via slow-solvent evaporation technique is reported. Screening for loss of viability in mammary carcinoma cells revealed that compounds such as 2[(4(2,3-dichlorophenyl)piperazin-1-yl][naphthalen-1-yl]methyl)phenol (4e), 5[(4(2,3-dichlorophenyl)piperazin-1-yl][2-hydroxyphenyl)methyl)uran-2-carbaldehyde (4f), 3[(2-hydroxyphenyl][4(p-tolyl)piperazin-1-yl)methyl)benzaldehyde (4i), and NPB inhibited the viability of MCF-7 cells with IC₅₀ values of 5.90, 3.11, 7.68, and 6.5 µM, respectively. The loss of cell viability was enhanced by the NPB analogs synthesized by adding newer rings such as naphthalene and furan-2-carbaldehyde in place of N-cyclopentyl-benzamide of NPB. Furthermore, these compounds decreased Ser99 phosphorylation of hBAD. Additional in silico density functional theory calculations suggested possibilities for other analogs of NPB that may be more suitable for further development. Full article

In this study, a water reattachment length was calculated by adopting two different models. The first was based on Unsteady Reynolds-Averaged Navier–Stokes (URANS) k-omega with Shear Stress Transport (SST); the second was a Large Eddy Simulation (LES) with Wall-Adapting Local Eddy-Viscosity (WALE). Both models used the same mesh and were checked with Taylor length-scale analysis. After the analysis, the mesh had 11,040,000 hexahedral cells. The geometry was a symmetrical expansion–contraction tube with a 4.28 expansion ratio that created mechanical energy losses, which were taken into account. Moreover, the reattachment length was estimated by analyzing the speed values; the change of speed value from negative to positive was used as the criterion to recognize the reattachment point. Full article