This paper presents a computational investigation of aero-optic aberrations that arise when multiple lateral jets are used to control a supersonic interceptor. Reynolds-averaged Navier–Stokes simulations are employed to examine the flow structure and evaluate the effects of various parameters, including altitudes ranging from 30–50 km, angles of attack (AOAs) from −15 to 25 deg, and four distinct jet configurations. the flow structure are analyzed by calculating the optical path difference (OPD) and normalizing it through scale analysis. When the jet flow does not interfere with the seeker’s field of view (FOV), the normalized OPD is predominantly governed by the bow shock and the conical expansion region in front of the vehicle head and exhibits similar profiles along the beam path for all altitudes. When the jet flow is introduced, the separation shock and bubble induced by jet interaction interfere with the seeker’s FOV at altitudes over 35 km and AOAs over 15 deg. Multijet cases at 35 km show that the separation bubble blocks a larger portion of the seeker’s FOV and increases the normalized OPD at higher AOA as the per-jet strength increases. For the most severe degradation case, unsteady delayed detached eddy simulation results predict a time-averaged normalized OPD that is about 20% larger than the steady-state counterpart.

The energetic performance of railway vehicles is becoming increasingly important, including for low-speed trains operating on regional and inter-city routes. Aerodynamic drag significantly affects train power consumption, making its accurate estimation essential for the design of energy-efficient rolling stock. Numerical simulations are widely used to estimate aerodynamic resistance; however, simplified fluid-dynamics approaches may lead to inaccurate predictions, particularly for the complex geometries typical of regional trains. This paper compares two numerical methods — Reynolds-Averaged Navier–Stokes (RANS), widely adopted in industry, and the state-of-the-art Improved Delayed Detached-Eddy Simulation (IDDES) — against wind tunnel experiments. Two train geometries are analysed: a conventional regional-train shape and a modified, more streamlined configuration. The analysis focuses on the global aerodynamic drag predicted by the numerical approaches and compares it with experimental measurements. Both methods show satisfactory agreement with the experiments, although noticeable differences emerge. Significant discrepancies are observed in highly turbulent regions, such as the tail, roof, and bogie areas, with IDDES consistently predicting higher drag levels than the RANS model. This work provides new insights into the aerodynamics of regional trains, a vehicle category that has received limited attention so far, and offers results of practical relevance to the railway industry. • Comparison between RANS and IDDES turbulence models for regional-train aerodynamics. • Effects of turbulence models on bluff and streamlined train geometries. • Evaluation of drag contributions along the train using sectional and cumulative aerodynamic coefficients. • Assessment of the influence of roof-mounted equipment and bogie geometry on drag prediction.

The physical mechanism of oscillatory instability in spiked-body flow at a freestream Mach number of 6 and a Reynolds number of 0.13 million, based on the cylinder diameter, is investigated using high-fidelity delayed detached-eddy simulation (DDES). The simulation successfully captures the unsteady shock structures and global flow features, enabling a detailed analysis of the underlying dynamics. A dominant low-frequency mode governing the large-scale oscillation is identified and shown to be intrinsically linked to the evolution of the complex coupled interaction among shock waves, shear layers, and separation regions. The oscillation cycle is characterized by the periodic advance and retreat of the separation zone, accompanied by the flapping motion of the separation shock and the shear layer. The bidirectional propagation of inner compression waves and their convection velocities are identified, revealing their key role in sustaining the feedback loop among the separation shock, shear layer, and recirculation region. These findings provide a new physical understanding of the origin and sustaining mechanism of large-scale oscillations in hypersonic spiked-body flows.

Research on the suppression method of bow wave plunging breaking for high-speed ships

This study presents a comparative numerical investigation of the hull–propeller–rudder interactions using Improved Delayed Detached Eddy Simulation (IDDES) for the free-running ONRT model under straight-line and astern operating conditions in calm water. Simulations demonstrate good agreement with experimental data, with a steady-speed error of 2.63%. The results reveal that astern navigation significantly increases total resistance and reduces attainable speed. The astern navigation also leads to a marked degradation of propeller performance, with a significant reduction in the wake fraction. While both conditions exhibit Kelvin-type wave patterns, the astern case shows distinct variations in wave elevation characteristics. The wake dynamics, critical to the hull–propeller–rudder interplay, undergo significant changes: the axial high-speed region and radial suction band shift upward, and tip-vortex instability intensifies with increased small-scale fragmentation. Furthermore, the secondary flow structures induced by these interactions differ substantially, particularly regarding the disappearance of bow-induced flows. This work elucidates how these interaction mechanisms and associated flow details are altered under astern navigation.

ABSTRACT This study investigated the fluctuating wind pressure distribution characteristics on the geometrically complex spatial structure of the Chengdu Future Science and Technology City Exhibition Center through an integrated approach combining wind tunnel testing with numerical simulations across multiple wind directions. The numerical simulation methodology was rigorously validated against wind tunnel experimental data prior to implementation. Utilizing the Consistent Discretizing Random Flow Generation (CDRFG) method for turbulent inflow boundary conditions and the delayed detached eddy simulation (DDES) approach for complex flow field resolution, the research systematically analyzed multiple key parameters: mean and fluctuating wind pressure coefficients, time‐domain correlation characteristics, surface vorticity distribution, and higher order statistical parameters including skewness, kurtosis, and peak factors. The findings demonstrate distinct spatial patterns in wind pressure correlation, with windward surfaces exhibiting strong coherence whereas leeward and side surfaces show significantly weaker correlation (typically 0.1–0.4, occasionally negative) due to vortex shedding and flow separation phenomena. Notably, the measured peak factors consistently exceeded the conventional 3.5 threshold, reaching maximum values of 6.11, indicating enhanced turbulence intensity that generates more extreme pressure distributions. Vorticity analysis reveals marked directional dependence, with a uniform distribution on windward surfaces contrasting with intense, intermittent shedding on side and leeward surfaces. The non‐Gaussian characteristics of pressure distributions are further confirmed by significant skewness (up to 1.11) and kurtosis (up to 7.12) values. These results collectively demonstrate the highly irregular nature of wind load distributions on complex‐shaped structures, emphasizing the necessity of accounting for these adverse effects in wind‐resistant design practices.

Abstract This study investigates the effect of small trim angles (±0.5°) on the bow wave breaking of the DTMB5415 hull at Fr=0.35 using Delayed Detached Eddy Simulation (DDES). The validated simulations reveal that trim angle fundamentally alters the breaking pattern: bow-up trim intensifies the breaking zone and spray, leading to more violent plunging, while stern trim promotes spilling breaking closer to the bow. Energy analysis shows that bow trim induces a “broad and persistent” energy transfer mode, in contrast to the “more concentrated and intense” mode under stern trim. Vorticity quantification within the defined breaking zone confirms the overall dominance of negative vorticity; bow trim enhances localized high-intensity positive vortices, whereas stern trim yields a more stable flow. Further, trim systematically reshapes the breaking zone’s three-dimensional morphology: bow trim reduces volume but increases surface area, exhibiting pronounced dispersion characteristics, whereas stern trim drives the zone toward a more cohesive structure. These morphological changes underpin the observed differences in energy distribution and vortex dynamics, providing a mechanistic link between trim alteration and the macroscopic hydrodynamic response.

Numerical investigations of flow fields around polyethylene terephthalate (PET) nets using Improved Delayed Detached Eddy Simulation

Adaptive detached eddy simulation of transitional and massively separated flows around the S809 airfoil

Currently, the operating speed of a certain metro line’s trains in the tunnel has reached 140 km/h and is advancing toward the target of 160 km/h, making it urgent to research the aerodynamic noise of metro trains in tunnel. This paper conducts numerical simulation research on the unsteady aerodynamic characteristics and noise of the metro trains on this line operating in the tunnel at speeds of 120, 140, and 160 km/h. The study first conducts steady-state calculations on a scaled-down train based on the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) method and the Shear Stress Transport (SST) k-ω turbulence model. Subsequently, the hybrid Improved Delayed Detached Eddy Simulation (IDDES) and Acoustic Perturbation Equations (APE) method is employed to complete the aerodynamic noise calculations at different speeds. The results indicate that the flow field structures in the train connecting frame, pantograph, underbody, and wake regions are relatively complex. Pressure fluctuations are more significant in areas such as the train’s connecting frame, pantograph, coupler, the first bogie of the head car, and the bottom of the tail car driver’s cab. The acoustic pressure fluctuations are larger in the bogie regions beneath the train. The sound pressure power spectral density at six bogie monitoring points exhibits five peaks. The findings of this study can serve as a reference for the control of aerodynamic noise in the metro trains on this line and for future speed increases in metro trains.

Evaluation of delayed detached eddy simulation with gray area mitigation techniques and enhanced protection of boundary layer

A porous wire mesh is employed to investigate flow control and noise reduction in landing gear. The numerical simulation is based on the improved delayed detached-eddy simulation method and the Ffowcs Williams–Hawkings equation. Aerodynamic noise prediction is first conducted for the baseline landing gear model, and the applicability of the porous wire mesh boundary condition is validated. Subsequently, two types of porous mesh structures are applied for noise reduction, both achieving significant noise suppression. Building on this, a parametric study on porosity is performed. It is found that when porosity is small, the flow characteristics resemble those of a solid fairing, with dominant noise originating from the wake region of the porous mesh; when porosity is large, the flow field approaches the baseline configuration, with noise dominated by interference between different landing gear components. The moderate porosity of 0.45 is identified as the optimal porosity. Both noise sources are effectively suppressed, yielding the maximum far-field noise reduction. Regarding aerodynamic forces, while the solid fairing significantly increases drag, the porous meshes mitigate this additional drag. The findings provide a theoretical basis for landing gear noise reduction design.

ABSTRACT This study employs an Improved Delayed Detached Eddy Simulation (IDDES) approach based on the SST k-ω turbulence model to characterize the turbulent flow over three-dimensional sinusoidal rough surfaces, an idealized model for periodic roughness found in marine applications such as biofouling or corrosion. A series of simulations were conducted for a range of roughness amplitudes ( h 0 / Ω = 0.033 − 0.142 ) and Reynolds numbers ( R e Ω = 4500 − 18000 ). The results demonstrate that the SST k-ω IDDES model successfully captures the mean flow characteristics and the roughness-induced shift in the mean velocity profile, the roughness function ( Δ U + ). A key finding is that for 3D sinusoidal roughness, the equivalent sand-grain height follows the relationship k s ≈ 18 h 0 2 / Ω . The computed roughness functions collapse onto a single curve when plotted against k s + and show good agreement with the classical sand-grain roughness correlation, particularly in the fully rough regime.

ABSTRACT The flow noise from submarines, an aspect of hydrodynamic noise, significantly affects their stealth capabilities. This study, utilizing the Elliptic Blending k − ϵ Delayed Detached Eddy Simulation model and the Ffowcs Williams-Hawkings equations, discusses the applicability of the two numerical models for submarine flow noise and acoustic sources calculations. The two models are the static model of water tunnel model and the dynamic model combined with overset mesh. The numerical methods of the flow and acoustic fields well match the experiments. The results reveal that similarity in flow field characteristics across both models determines that the dipole noise sources are similar. The dynamic model radiates two types of far-field noise: loading and thickness noise. This research introduces the ‘noise source family’ concept to categorize noise sources, revealing the evolution mechanism of far-field noise. The loading and thickness noise is classified as stable and fluctuating regions based on the frequency spectrum. The mechanism for the formation of the fluctuating region is investigated according to the evolution regulation of the noise sources. Spatial-frequency spectrum properties of noise directivity are further explored.

Simplified Reynolds-stress model based detached eddy simulations in fixed coordinate system

Development of an improved delayed detached eddy simulation method for particle-laden flow including resuspension

As high-speed train speeds continue to rise, traditional friction braking fails to deliver efficient emergency braking—making aerodynamic braking devices (ABDs) a key solution for boosting high-speed train operational safety. However, the internal cavity structures of ABDs induce complex flow-induced vibrations and aerodynamic instabilities, which not only impair the train's aerodynamic performance but also threaten its operational safety. This study focuses on the length-depth ratio (L/D) of cavity structures in high-speed train ABDs, aiming to investigate how this key geometric parameter influences the flow field structure, aerodynamic characteristics, and vibration characteristics of ABDs. To address this research objective, the study adopts computational fluid dynamics based on the improved delayed detached eddy simulation model—this model is used to simulate the unsteady flow field structures of ABDs with different L/D, while unsteady aerodynamic characteristics of the devices are further analyzed in both time and frequency domains. Additionally, a vehicle system dynamics model is established to further analyze the effects of varying L/D on the train's vibration responses and ride comfort. The results show that L/D regulates the vortex shedding mechanism of ABDs: at L/D = 2.5, compact high-frequency vortices cause prominent drag fluctuations; cavity pressure pulsations have a moderate positive correlation with L/D, peaking at 7678.5 Pa when L/D = 10. Installing ABDs reduces the axle lateral force by 18.7%–22.1%, and L/D = 5 optimizes lateral performance while maintaining vertical stability. This work verifies ABDs' applicability and clarifies the aerodynamic-vibration coupling mechanism, providing a theoretical basis for aerodynamic braking system design.

A numerical study is performed to investigate the effects of spacing ratio on the three-dimensional unsteady flow dynamics and axis-switching behavior of in-phase circular twin synthetic jets (TSJs) using Improved Delayed Detached Eddy Simulation. The simulations were performed at a fixed Reynolds number (Re=130) and dimensionless stroke length (L0/d=15.7), across four spacing ratios (s/d=1.2, 2.0, 3.0, and 4.0). The study uses time- and phase-averaged statistics, Q− criterion, and vortex circulation to characterize the evolution of vortical structures and jet-to-jet interference. The results show that jet interactions are enhanced as the spacing ratio decreases, promoting earlier merging of inner shear layers and the formation of coherent vortex ring pairs. The merging and combined points increased linearly with increasing spacing ratio. An axis-switching phenomenon, typically associated with non-circular jets, is induced in the circular TSJs through vortex interactions occurring at low spacing ratios (s/d≤3.0). As a result, the mean velocity decay, lateral spread rates, and vorticity redistribution in the TSJs are enhanced as the spacing ratio decreases.

This study employed the Improved Delayed Detached Eddy Simulation (IDDES) method with the Synthetic Eddy Method (SEM) for turbulent inflow generation to conduct high-fidelity numerical simulations of complex flow within a three-dimensional U-bend pipe. The study focused on comparing simulation results against experimental measurements for axial velocity distributions, wall friction coefficients, and pressure coefficients at various axial locations. The results demonstrate that the SEM-IDDES approach accurately simulates fully developed flow within the straight sections of the U-bend pipe, capturing key flow characteristics such as the streamwise velocity profile and wall friction coefficient distribution. Furthermore, to address the strong curvature effects inherent to the bend section, a Curvature Correction (CC) model was incorporated, leading to the development of the SEM-IDDES-CC model. This enhancement aimed to evaluate the impact of curvature correction on the simulation accuracy of curved pipe flow. Comparative analysis revealed that the SEM-IDDES-CC model, incorporating curvature correction, significantly outperformed the baseline SEM-IDDES model in capturing the complex flow features within the bend region. The simulation results obtained with the SEM-IDDES-CC model exhibited markedly improved agreement with the experimental data.

To investigate the effectiveness of open-loop control in mitigating thermoacoustic instability in a model high-pressure, turbulent rocket combustor, this paper presents different synchronization routes to lock-in at two external sinusoidal forcing frequencies under dynamic systems theory. To achieve this, a full-scale three-dimensional detached eddy simulation is conducted with periodic forcing applied at a constant propellant mass flow rate to explore interactions between thermoacoustic instability (oscillating at f1≈1566 Hz) and external sinusoidal forcing (oscillating at ff). Additionally, a forced nonlinear universal oscillator based on the Duffing–Van der Pol (DVDP) model is developed to characterize synchronization dynamics. Results show that as the amplitude of the external forcing gradually increases (0%≤A≤65%), at ff=0.88f1, a quasi-periodic route to lock-in emerges; at ff=1.12f1, an intermittency route to lock-in appears, with the amplitude reaching a minimum, indicating an optimal open-loop control strategy. The DVDP model qualitatively reproduces the quasi-periodic route to lock-in but fails to capture intermittency due to turbulence-induced stochasticity. Phase-locking and frequency-locking between acoustic pressure and heat release oscillations—driven by partially premixed combustion modes including premixed and diffusion flames—are identified as the key physical mechanisms underlying the bifurcation process under the open-loop control framework of thermoacoustic instability.