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The slipstream caused by high-speed trains may harm pedestrians and workers trackside. In general, the characteristics of the slipstream are influenced mainly by the nose shape of the train. The present study explores the slipstream caused by high-speed trains with three different horizontal nose profiles based on the results of three-dimensional, improved delayed detached eddy simulation (IDDES) with an unsteady turbulence model and a set of 1/8th scaled train models. The results obtained using this numerical methodology are in good agreement with those obtained from corresponding wind tunnel tests. The trackside pressure changes around the train models are also captured and analyzed. The analysis reveals that the width of the nose can significantly influence the magnitude and arrival time of slipstream velocity and pressure peaks. The results and proposed numerical methodology can be used as guidelines for the design of high-speed train nose shapes.

Turbine cooler is the dominant cabin noise source of air conditioning system during aircraft ground and flight operation. The noise impact on passengers’ health can no longer be ignored, so modern commercial aircraft air conditioning system must meet low noise requirements. In this paper, turbine cooler transient flow field was calculated by detached-eddy simulation (DES), and its discharge noise is investigated using FW-H theory. The simulation analysis results and test data show that computational aeroacoustics (CAA: DES and FW-H combined method) can effectively capture the turbine cooler discharge noise level. The authors also present details related to the contribution of its blade passing frequency (BPF) and turbulence noise.

Floating offshore wind development requires an improved understanding of wake dynamics influenced by platform motions. Pitch and roll motions significantly influence wake behavior, especially in low to moderate turbulence, affecting downstream turbines. This study employs an improved delay detached eddy simulation (IDDES) with a blade-resolved approach to analyze the wake characteristics of a floating offshore wind turbine (FOWT) subjected to harmonic pitch and roll motions. Using a sliding interface approach, turbine rotation, and oscillatory dynamics are modeled. Considering only the turbine rotor, the wake dynamics of the moving and stationary cases are compared. The simulation results show good agreement with the available experimental data, confirming their validity. The results show that platform motions increase wake unsteadiness, enhance turbulence mixing, and accelerate far-wake recovery through coherent flow structures. Larger motion amplitudes lead to earlier onset of wake structures - 34% for pitch and 42% for roll - increasing turbulence and velocity deficit. Probability density functions of the wake reveal that roll motion significantly broadens the lateral wake, increasing turbulence. In contrast, pitch motion results in a more balanced and stable wake displacement in both lateral and vertical directions.

The wake and the lack of existing velocity behind the wind turbine affect the energy production and the mechanical integrity of wind turbines downstream in the wind farms. This paper presents an investigation of the unsteady flow around a wind turbine under yawed condition. The simulations and experimental measures are made for the yaw angle rotor 30[degrees] and 0[degrees]. The wind velocity is 9.3 m/s and the rotation velocity rotor of the wind turbine in 1300, 1500 and 1800 rpm. The wind turbine rotor which is modeled is of a commercial wind turbine i.e. Rutland 503. The approach Improved Delayed Detached Eddy Simulation (IDDES) based on the SST turbulence model is used in the modeling of the flow. The solutions are obtained by using the solver which uses finite volume method. The particle image velocimetry (PIV) method is used in wind tunnel measurements in the experimental laboratory of the ENSAM Paris-Tech. The yawed downstream wake of the rotor is compared with that obtained by the experimental measurements. The results illustrate perfectly the development of the near and far wake of the rotor operation. It is observed that the upstream wind turbine yawed will have a positive impact on the power of the downstream turbine due the distance reduction of the downstream wake of the wind turbine. However the power losses are important for yawed wind turbine when compared with the wind turbine without yaw. The improved understanding of the unsteady environmental of the Horizontal Axis wind Turbine allows optimizing wind turbine structures and the number of wind turbines in wind farms.

Unsteady cloud cavitating flow is detrimental to the efficiency of hydraulic machinery like pumps and propellers due to the resulting side-effects of vibration, noise and erosion damage. Modelling such a unsteady and highly turbulent flow remains a challenging issue. In this paper, cloud cavitating flow in a venturi is calculated using the detached eddy simulation (DES) model combined with the Merkle model. The adaptive mesh refinement (AMR) method is employed to speed up the calculation and investigate the mechanisms for vortex development in the venturi. The results indicate the velocity gradients and the generalized fluid element strongly influence the formation of vortices throughout a cavitation cycle. In addition, the cavitation-turbulence coupling is investigated on the local scale by comparing with high-fidelity experimental data and using profile stations. While the AMR calculation is able to predict well the time-averaged velocities and turbulence-related aspects near the throat, it displays discrepancies further downstream owing to a coarser grid refinement downstream and under-performs compared to a traditional grid simulation. Additionally, the AMR calculation is unable to reproduce the cavity width as observed in the experiments. Therefore, while AMR promises to speed the process significantly by refining the grid only in regions of interest, it is comparatively in line with a traditional calculation for cavitating flows. Thus this study intends to provide a reference to employing the AMR as a tool to speed up calculations and be able to simulate turbulence-cavitation interactions accurately.

The flow over alternating roughness strips oriented normally to the mean stream is studied using wall-modeled large-eddy simulations (WMLES) and improved delayed detached-eddy simulations (IDDES) (a hybrid method solving the Reynolds-averaged Navier–Stokes (RANS) equations near the wall and switching to large-eddy simulations (LES) in the core of the flow). The calculations are performed in an open-channel configuration. Various approaches are used to account for roughness by either modifying the wall boundary condition for WMLES or the model itself for IDDES or by adding a drag forcing term to the momentum equations. By comparing the numerical results with the experimental data, both methods with both roughness modifications are shown to reproduce the non-equilibrium effects, but noticeable differences are observed. The WMLES, although affected by the underlying equilibrium assumption, predicts the return to equilibrium of the skin friction in good agreement with the experiments. The velocity predicted by the IDDES does not have memory of the upstream conditions and recovers to the equilibrium conditions faster. Memory of the upstream conditions appears to be a critical factor for the accurate computational modeling of this flow.

This study conducts a comparative analysis between detached eddy simulation (DES) and Unsteady Reynolds-averaged Navier-Stokes (URANS) models for simulating pressure fluctuations in a stilling basin, aiming to assess the URANS mode’s performance in modeling pressure fluctuation. The URANS model predicts accurately a smoother flow field and its time-average pressure, yet it underestimates the root mean square of pressure (RMSP) fluctuation, achieving approximately 70% of the results predicted by DES model on the bottom floor of the stilling basin. Compared with DES model’s results, which are in alignment with the Kolmogorov −5/3 law, the URANS model significantly overestimates low-frequency pulsations, particularly those below 0.1 Hz. We further propose a novel method for estimating the RMSP in the stilling basin using URANS model results, based on the establishment of a quantitative relationship between the RMSP, time-averaged pressure, and turbulent kinetic energy in the boundary layer. The proposed method closely aligns with DES results, showing a mere 15% error level. These findings offer vital insights for selecting appropriate turbulence models in hydraulic engineering and provide a valuable tool for engineers to estimate pressure fluctuation in stilling basins.

Turbulent flow fields over a two-dimensional steep ridge and three-dimensional steep hill with rough and smooth surfaces are investigated by using a delayed detached-eddy simulation (DDES) with the specified height as a new control parameter. The applicability of typical turbulence models in previous studies is evaluated by using validation metrics. While all turbulence models simulate the turbulent flow fields over the steep rough terrain well, the k − ε model overestimates the mean wind speed and underestimates the turbulent kinetic energy over steep, smooth terrain. The large-eddy simulation captures the large-scale vortices and improves the mean wind speed, but overestimates the turbulent kinetic energy due to the inaccurate specification of the surface roughness. The detached-eddy simulation considering the surface roughness shows further improvement, but still overestimates the turbulent kinetic energy, since the region using the Reynolds-averaged Navier–Stokes model is too thin. The modified DDES model with a new control parameter is suitable for the prediction of the mean wind speed and turbulence as demonstrated by the visualization of instantaneous flow fields through vortex cores, and a quadrant analysis to examine the organized motion, with strong organized motions identified in the wake region of smooth terrain. Roller vortices are significant on the lee side of the two-dimensional smooth ridge, while horseshoe vortices appear in the wake region of the three-dimensional smooth hill.

Ship bow wave breaking is a common phenomenon during navigation, involving complex multi-scale flow interactions. However, the understanding of this intense free surface flow issue is not sufficiently deep, especially regarding the lack of research on the impact of scale effects on bow wave breaking. This paper focuses on the benchmark ship model KCS and conducts numerical simulations and comparative analyses of bow wave breaking for three model scales under the condition of Fr = 0.35 . The numerical calculations were performed using the in-house computational fluid dynamics (CFD) solver naoe-FOAM-SJTU, which is developed on the open source platform OpenFOAM. Delayed detached eddy simulation (DDES) method is utilized to calculate the viscous flow field around the ship hull. The present method was validated through measurement data of wave profiles and wake flows obtained from model tests. Flow field results for three different scales, including bow wave profiles, vorticity at various sections, and wake distribution, were presented and analyzed. The results indicate that there is small difference in the bow wave overturning and breaking for the first two occurrences across different scales. However, considerable effects of scale are observed on the temporal and spatial variations of the free surface breaking pattern after the second overturning. The findings of this study can serve as valuable data references for the analysis of scale effects in ship bow wave breaking phenomena.

The leakage flow has a significant impact on the aerodynamic losses and efficiency of the compressor. This paper investigates the loss mechanism in the tip region based on a high-load cantilevered stator cascade. Firstly, a high-fidelity flow field structure was obtained based on the Enhanced Delay Detached Eddy Simulation (EDDES) method. Subsequently, the Liutex method was employed to study the vortex structures in the tip region. The results indicate the presence of a tip leakage vortex (TLV), passage vortex (PV), and induced vortex (IV) in the tip region. At i=4°,8°, the induced vortex interacts with the PV and low-energy fluid, forming a “three-shape” mixed vortex. Finally, a qualitative and quantitative analysis of the loss sources in the tip flow field was conducted based on the entropy generation rate, and the impact of the incidence on the losses was explored. The loss sources in the tip flow field included endwall loss, blade profile loss, wake loss, and secondary flow loss. At i=0°, the loss primarily originated from the endwall and blade profile, accounting for 40% and 39%, respectively. As the incidence increased, the absolute value of losses increased, and the proportion of loss caused by secondary flow significantly increased. At i=8°, the proportion of secondary flow loss reached 47%, indicating the most significant impact.