Delayed Detached Eddy Simulation Research Articles

Delayed detached eddy simulation for wake flow analysis of axisymmetric boattail models under low-speed conditions

This study investigates the steady and unsteady behaviors of near-wake flow for axisymmetric models acquired with conical boattails with different slant angles under low-speed conditions. Delayed detached eddy simulation (DDES) was applied for the numerical processes. The Proper Orthogonal Decomposition (POD) was then used to reconstruct the dominant modes of the pressure at the base and velocity fields on the symmetry plane. Both near-wake and far-wake flows were considered in this study to obtain a full pattern of the wake. It was shown that the DDES allows for obtaining a highly accurate wake flow field. The large-scale structure of the base flow with two dominant modes of vortex shedding at StD = 0.19–0.24 and bubble pumping at StD = 0.06–0.08 occurs for the axisymmetric blunt-based model. At boattail angles up to 16°, those frequencies are clearly distinguished from the time series of POD modes of the velocity fluctuations. However, for higher angles, the motions of the “bubble pumping” and vortex shedding combine to generate frequencies in the range of StD = 0.07–0.15. The fully separated flow disturbs a ratio of one-third for the bubble pumping and vortex shedding frequencies, which was shown widely in previous studies. The reduction of frequency band and large-scale features for boattail angles of 16° explains the low drag generated for that configuration.

Numerical predictions of underwater radiated noise from a non-cavitating model-scale propeller

Propeller-induced acoustic noise from marine vessels is the largest source of anthropogenic underwater radiated noise (URN) and a significant threat to marine ecosystems. Under typical operation, cavitation dominates the URN emissions. Cavitation, which is a pressure-driven phase-change process that results in the violent formation and collapse of vapor bubbles in the wake of the propeller, is often unavoidable during realistic, full-scale operating conditions. However, at a model scale, inducing cavitation requires a depressurized flow facility that makes acoustic measurements difficult due to confinement effects. Numerical simulation is, therefore, appealing as a tool for predicting URN, but the simulation of the cavitation phenomenon and the associated acoustics involves considerable uncertainty and a range of potential sources of error. In propeller operation, cavitation frequently occurs in the core of the vortices shed from the tips of propeller blades. In the present work, we developed a delayed detached-eddy simulation (DDES) of a model-scale ship with the focus on predicting fluctuating pressure due to shed vorticity. The solution is compared to hydrophone measurements from non-cavitating tow-tank experiments. Finally, we numerically introduce cavitation at model scale in the numerical solution and examine its effects.

Mid-fidelity NATO generic destroyer static and moving-ship airwake simulations using the Lattice-Boltzmann method compared with experimental data

During rotorcraft ship-deck landing operations, complex interactional aerodynamic phenomena occur between the rotor and ship airwakes which are not fully understood. To aid in ship–rotorcraft interactional investigations, efficient mid-fidelity ship airwake solutions are needed. Additionally, the effects of ship motion have not been explored much. In this study, the NATO Generic Destroyer, a shared, representative ship geometry created for collaborative studies, was investigated numerically using a GPU-accelerated Lattice-Boltzmann Method solver, and the ship airwake results compared with wind tunnel measurements using discrete velocity probes on the landing deck. The ship surface was modeled using a robust Grad immersed boundary approach, and ship motion was thereby included in the simulations. Ship airwake results showed good agreement with the experiment and excellent computational performance. Simulations took under four hours to run on a single GPU node. This is several orders of magnitude improvement over traditional Delayed Detached-Eddy Simulations typically used to solve this problem, which may take days or weeks on CPU-based HPC clusters.

Transitional Delayed Detached-Eddy Simulation for a Compressor Cascade: A Critical Assessment

The accurate prediction of transitional flows is crucial for the industrial turbomachinery design process. While a Reynolds-averaged Navier–Stokes approach inherently brings conceptual weaknesses, large-eddy simulation will still be too expensive in the near future to affordably analyze complex turbomachinery configurations. We introduce a transitional delayed detached-eddy simulation (DDES) model, namely, DDES-γ, and analyze the numerical results of the compressor cascade V103. A comparison with the fully turbulent DDES approach emphasizes the benefit of coupling DDES with a transition model. Issues with undesired decay of modeled turbulent kinetic energy in the freestream are improved when running DDES-γ in combination with the synthetic turbulence generator method. The best results for DDES-γ are obtained when changing the inviscid flux solver blending from dynamic to constant mode. We show that DDES-γ is capable of predicting the transitional flow through a linear compressor cascade, but we also critically discuss the general concept and results.

Numerical analysis of the influence of hull-modulated inflow on unsteady force fluctuations and vortex dynamics of pump-jet propulsor

The influence of the hull-modulated inflow on the propulsion performance of the propeller is related to the matching design of the propeller–hull system. In the present study, considering the working conditions of the pump-jet propulsor in uniform inflow and two types of hull-modulated inflow, based on improved delay detached eddy simulation, the influence of hull-modulated inflow on unsteady force fluctuations and vortex dynamics of pump-jet propulsor under design conditions is carried out. The results show that the hull-modulated inflow increases the propulsion efficiency of the pump-jet propulsor to varying degrees within the range of the calculated advance coefficient and has a significant influence on the frequency characteristics of the unsteady force spectra characteristics of each component of the pump-jet propulsor. It also shows changes in the magnitude characteristics, that is, the energy transfer process of an individual rotor blade from the stator blade passing frequency to other harmonics of the shaft rotation frequency, and the thrust spectrum of an individual stator blade presents broad-spectrum characteristics in the high-frequency range. Furthermore, the application of hull-modulated inflow directly affects the shape of the stator shedding vortex, causing some of the stator blade shedding vortices to separate early and aggravating its short-wave instability. More secondary vortices are induced to accelerate the instability of the rotor blade tip clearance vortex. The energy transfer mechanism from the rotor blade passing frequency and its harmonics to the broadband spectra appears in the wake field of the pump-jet propulsor.

Assessment of the DDES-γ Model for the Simulation of a Highly Loaded Turbine Cascade

Abstract The flow over the linear low-pressure turbine cascade MTU-T161 at Re = 90,000 is analyzed using delayed detached eddy simulations (DDES). At this operating point, the low Reynolds number and the high loading of the blade result in a separation bubble and a separation-induced transition of the flow over the suction side. The utilized DDES method is based on a vorticity-based formulation to calculate the subgrid length scales, and it incorporates the one-equation γ-transition model. The computational model of the MTU-T161 cascade consists of one blade passage, including the diverging viscous sidewalls. To reproduce realistic operating conditions and to mimic the experiments, synthetic turbulence is prescribed at the inlet of the computational domain. Several studies are performed to assess the accuracy and performance of the DDES one-equation γ-transition model against experimental data and a benchmark large eddy simulations (LES). The primary focus is on the prediction of the separation and the separation-induced transition mechanism. First of all, a systematic grid convergence study is conducted and grid criteria are derived in order to ensure a satisfactory agreement of the flow metrics, such as isentropic Mach number, friction coefficient distribution, and total pressure wake losses at mid-span with experimental data. Furthermore, a detailed analysis of the DDES model parameters, such as shielding function and subgrid length scale, is presented and the effect of these parameters on the prediction accuracy of the separation bubble region is analyzed. The analysis of the suction side boundary layer indicates that the turbulent kinetic energy should be resolved and modeled properly in order to represent the separation bubble correctly. In particular, the correct prediction of the separated shear layer above the separation bubble is of utmost importance. The results of the simulations reveal higher demands on grid resolution for such transitional flows than typically have been reported in the literature for turbulent boundary layers. This higher demand on grid resolution results in more expensive simulations than Reynolds-averaged Navier–Stokes (RANS). Nevertheless, DDES requires less computing time than wall-resolved LES. Additionally, the results of the transitional DDES model are compared to DDES without a transition model, an RANS eddy viscosity model, and a reference LES. The results show that the DDES approach needs to be coupled with a transition model, such as the one-equation γ-transition model, in order to capture the flow topology over a highly loaded turbine blade correctly. The benefit of the DDES one-equation γ-transition model becomes particularly evident when predicting the separated shear layer, the transition process, and the subsequent reattachment. The RANS eddy viscosity turbulence and transition models applied within our study are not able to predict the aforementioned mechanisms accurately. For highly loaded turbine blades in particular, the accurate prediction of flow separation and potential reattachment is crucial for the aerodynamic design of turbines, since large parts of the total pressure loss are generated in the separated region. For this reason, the DDES one-equation γ-transition model can be a good compromise in terms of predictive accuracy and computational costs.

Sensitivity Analysis of an Unsteady Flow Around a Pitching Airfoil

Various ways to control the loads and thus the output of the wind turbine by pitching the blades and by controlling the rotational speed already exist. However, adverse pressure gradient leading to flow separation at the trailing edge, with relatively high angles of attack (AOA) due to blade-pitching motion, largely affects the airfoil aerodynamic performance. This work presents the results of a numerical study of the unsteady flow around a pitching FFA-W3-301 airfoil at a Reynolds 1.6 × 106 using OpenFOAM®, as obtained by first performing 2D Unsteady Reynolds-Averaged Navier- Stokes (URANS) simulations whereby the flow characteristics are simulated by the shear stress transport (SST) k − ω model and Spalart-Allmaras (SA). The influence of various parameters on the numerical results is investigated, namely y+, computational grid resolution, dynamic mesh technique, time step and turbulence model. Integral aerodynamic forces and detailed flow patterns are compared with experimental measurements presented in the literature. A range of angles of attack, including early stalls, are examined. For best-performing parameters, an adequate refinement close to the wall was imperative in order to match experiments, especially during the upstroke motion of the airfoil, while for the downstroke phase, some differences still appeared. The agreement was greatly improved by using a 2.5D hybrid RANS-LES approach with enhanced delayed-Detached Eddy Simulation (DES) capabilities.

Effect of Blade Trimming Length on the Performance of Marine Centrifugal Pump

To study the hydrodynamic characteristics of blade trimming length in centrifugal pumps, Delayed Detached Eddy Simulation (DDES) with nonlinear eddy viscosity was utilized to conduct unsteady calculations on the centrifugal pump. A comprehensive examination of the fluid dynamic properties of the centrifugal pump, including external features, flow conditions, and pressure fluctuations, was carried out. By applying the theory of entropy production, the areas of high energy loss within the centrifugal pump were identified, and the correlations between local entropy production, energy loss, and unsteady flow in different areas with varying blade trimming lengths were analyzed. The results indicate that with the increase in blade trimming length, under rated flow conditions, the head decreases by 1.8%, 3.2%, and 5.7% for different blade trimming lengths, respectively, compared to normal impellers. Similarly, the efficiency decreases by 0.5%, 0.8%, and 1.0% for different blade trimming lengths, respectively. Similar trends were observed under other working conditions as well. As the degree of blade trimming increases, the irreversible losses after the failure of the centrifugal pump also increase significantly, indicating that the flow inside the centrifugal pump becomes disorder. Blade trimming leads to a disorderly fluid flow inside the centrifugal pump, causing an increase in the radial force during operation, which in turn leads to an increase in vibration amplitude and affects its operational stability. Blade trimming failure has a significant impact on the frequency and amplitude of pressure pulsation, resulting in abnormal pressure pulsation and abnormal vibration of the centrifugal pump. Therefore, early warning and diagnosis of blade trimming can be achieved through pressure pulsation monitoring.

Noise Prediction and Plasma-Based Control of Cavity Flows at a High Mach Number

Cavity flows are a prevalent phenomenon in aerospace engineering, known for their intricate structures and substantial pressure fluctuations arising from interactions among vortices. The primary objective of this research is to predict noise levels in high-speed cavity flows at Mach 4 for a rectangular cavity characterized by an aspect ratio of L/D = 7. Moreover, this study delves into the influence of the plasma actuator on noise control within the cavity flow regime. To comprehensively analyze acoustic characteristics and explore effective noise reduction strategies, a computational fluid dynamics technique with the combination of a delayed detached eddy simulation (DDES) and plasma phenomenological model is established. Remarkably, the calculated overall sound pressure level (OASPL) and plasma-induced velocity closely align with the experimental data, validating the reliability of the proposed approach. The results show that the dielectric barrier discharge (DBD) plasma actuator changes the movement range of a dominating vortex in the cavity to affect the OASPL at the point with the maximum noise level. The control of excitation voltage can reduce the cavity noise by 2.27 dB at most, while control of the excitation frequency can only reduce the cavity noise by 0.336 dB at most. Additionally, the increase in excitation frequency may result in high-frequency sound pressure, but the influence is weakened with the increase in the excitation frequency. The findings highlight the potential of the plasma actuator in reducing high-Mach-number cavity noise.

Visualization of pressure fluctuation characteristics of weapon bay on unmanned aerial vehicle using delayed detached eddy simulation

In the present study CFD simulation with delayed detached eddy simulation (DDES) are performed to investigate pressure fluctuation environment on an open cavity and weapon bay of UAV. The main purpose of this study is to explore the aerodynamic noise level of complex cavities with slant ceiling and irregular length–depth ratio. First, two cases on an open cavity at Ma 0.85 are analyzed to determine the slant ceiling influence, which shows that the sound pressure levels increase by 1 dB due to the transverse flow effect. Then, a typical weapon bay on unmanned aerial vehicle is simulated to investigate the aerodynamic noise environment. The overall sound pressure level in the weapon bay is up to 157 dB, and when the Mach number turns from 0.6 to 0.8, the amplitude of all modes increases about 16–23 dB. The main focuses of this investigation are to discuss the mechanism of noise generation in a slant ceiling cavity and determine the pressure fluctuation characteristic of a typical weapon bay on unmanned aerial vehicle.Graphical abstract

A Numerical Study of the Hydrodynamic Noise of Podded Propulsors Based on Proper Orthogonal Decomposition

Podded propulsors have become a focal point of research in the field of marine propulsion in recent years due to their high efficiency, low noise, and excellent maneuverability. To investigate the acoustic characteristics induced by the flow field of podded propulsors, a high-precision unsteady numerical simulation was conducted using the Delayed Detached Eddy Simulation (DDES) coupled with Ffowcs Williams–Hawkings (FW-H) equations. Multiple spatial acoustic receiving arrays were employed, and analysis methods including Proper Orthogonal Decomposition (POD) and Fast Fourier Transform (FFT) were utilized to determine the spatial distribution of the acoustic field of the podded propulsor. The results show that the blade passing frequency and the shaft frequency consistently dominate as the primary characteristic frequencies. On the plane of the propeller disk, the distribution of sound pressure levels is uniform without distinct directivity. Across the space curved surface, approximately the first ten POD modes encompass 99.8% of the total energy, and their spatial distribution characteristics of sound pressure are closely related to the pod structure. Additionally, these modes exhibit characteristic frequencies such as the blade passing frequency and shaft frequency. The spatial distribution of sound pressure at a single frequency on the spatial surface corresponds well with the results obtained from the POD analysis.

Numerical investigation of aero-optical effects around the turret based on delayed detached eddy simulation and unsteady Reynolds averaged Navier-Stokes

Delayed Detached Eddy Simulation (DDES) and Unsteady Reynolds Averaged Navier-Stokes (URANS), based on the two-equation Shear Stress Transport (SST) model, are implemented to investigate the flow features and the aero-optical distortions around the turret. The Mach number is Ma = 0.4 and the Reynolds number is Re = 1.43 × 106. Instantaneous and time-averaged flow fields are presented to compare the ability of DDES and URANS in predicting the flow features. The instantaneous results show that DDES can resolve the abundant flow structures and more disordered density distributions than URANS. The time-averaged pressure coefficient and the density distribution of both methods are generally similar, but the time-averaged turbulent kinetic energy of URANS is far higher than that of DDES. The time-averaged pressure coefficient of DDES is closer to experimental data. In the windward view, typical surface flow features of DDES and URANS are similar. In the leeward view, there are remarkable differences of typical flow features between DDES and URANS. At the six angles of elevation, 60°, 76°, 90°, 103°, 120°, and 132°, the spatial-temporal wavefront distortions are calculated and discussed with the geometric ray-tracing method and the Zernike polynomial fitting, respectively. In spatial distribution, the wavefront distortions of DDES and URANS are slightly different from the experimental data. At the angles of 60°, 76°, 90°, and 103°, the tendencies of wavefront distortion of DDES at different tracing distances are the same with that of URANS, which is due to the same ability of two methods to resolve the density distributions in the attached flow region. However, the results of DDES agree well with the experimental results at the angles of 120° and 132°, which is bigger than the results of URANS. For temporal characteristics, the frequencies of wavefront distortions of DDES are obviously higher than that of URANS. The amplitudes of wavefront distortions by DDES are about 3 to 5 times higher than that by URANS. At the cases of two different FLHs at Ma = 0.4, the flow structures are totally similar, and the tendencies of wavefront distortion with θ are also similar. At the cases of three Mach number, the compression has a big influence on the wavefront distortion.

A comprehensive assessment on detached eddy simulation and delayed detached eddy simulation approaches in large-scale rotating separated flow in a centrifugal impeller under small flow rate

This work performed a comprehensive comparative assessment on the capabilities and performances of detached-eddy simulation (DES) and delayed detached-eddy simulation (DDES) approaches in revealing the flow physics in a six-blade centrifugal impeller under a small flow rate. The numerical results are well validated by the experimental data of a similar configuration and are compared with the benchmark data generated by an additional large-eddy simulation investigation. The results are presented and analyzed in terms of the time-averaged flow field, the transient flow, and momentum transport characteristics. The capabilities of DES and DDES approaches in predicting the rotating turbulent flow are compared and assessed. The numerical results show that DES performs better in the pressure distribution, while DDES is superior in resolving the transient evolution of velocity field, especially the fluctuation quantities and turbulent statistical quantities. It is also emphasized that both approaches perform distinctly in quantifying the patterns of internal flow in different regions within the centrifugal impeller.

The effects of domain division types on the performance prediction of a rim-driven thruster

The rim-driven thruster (RDT) is an innovative propulsion thruster. The rotating subdomain can contain different assemblies with different domain division types (DDT). This paper tried to figure out the effects of DDT on the performance of RDT. This paper uses the Delayed Detached Eddy Simulation (DDES) turbulence model to conduct the simulations. Three DDTs are carefully analyzed to understand their effects on predictive performance. The convergence analysis is performed by taking a typical method: Grid Convergence Index (GCI). Some theoretical results and the experimental hydrodynamics of a popular combination of Ka 4–70 and MARIN 19 A are used to validate the numerical method. The numerical results demonstrate that the computational efficiency is influenced by the cell number on the interfaces between two subdomains and an inherent characteristic of DDT. Moreover, the torques acting on rim surfaces are closely accounting for the gap flow. Moreover, regarding the morphology and variables of the vortex system, the third type of DDT enhances vortices presenting in the hub region and vortex-instability region. Although the present analysis is performed for an RDT, the findings should be generally applicable for other RDT designs with similar structures and operational conditions.

Improved prediction of low-pressure turbine wake mixing by Delayed Detached Eddy Simulation, including an algebraic model for bypass transition

We present a hybrid RANS-LES technique of the Delayed Detached Eddy Simulation (DDES) form for transitional flow through low-pressure turbine blade cascades. A first ingredient is representation in RANS-mode of the flow that approaches the blades and the flow near the blade surfaces. The objective is to provide the correct level of modelled turbulent kinetic energy to an algebraic model for bypass transition which is coupled to a turbulence model, and thus simulation of bypass transition in attached boundary layer state by a RANS-model component. A second ingredient is resolution of the Kelvin-Helmholtz instability of a laminar separated boundary layer in RANS-mode, with transition in RANS-mode by a model component or transition in LES-mode by resolved breakdown. The third ingredient is representation in LES-mode of a wake flow and a separated layer that enters a wake, such that the wake mixing is by resolved fluctuations. For realisation of the RANS-zones and the LES-zones, we derive an appropriate sensor function. We demonstrate the good functioning of the technique for transitional flows of different types.

Delayed detached eddy simulation-based aerothermoelastic analysis of deployable control fin in supersonic and hypersonic flows

In the present work, nonlinear aerothermoelastic characteristics of a deployable control fin subjected to high supersonic and hypersonic flow are investigated. The delayed detached eddy simulation (DDES)-based computational fluid dynamics solver is strongly coupled to the finite element method-based structural dynamics and thermoelastic solver to perform coupled fluid-thermal-structural interaction analysis. A shear stress transport (SST) k−ω based DDES model is used for turbulence modeling, whereas the advection upstream splitting method scheme is used for flux calculation, and for dynamic meshing, a diffusion-based smoothing method is used. To solve the governing nonlinear structural dynamics equations of motion in the time domain, the Hilber–Hughes–Taylor (HHT)-α method is used with the Newton–Raphson linearization technique. Profile preserving and conservative mapping-based interfacing modules are used to couple the different solvers. For the validation of the methodology, two experimental test cases are considered, and the computations are in very good agreement with the experimental results. Furthermore, the effects of Mach number, angle of attack, and joint freeplay on the fin's structural and aerodynamic characteristics are investigated and presented. The results show a complex flow behavior over the fin including several separation and attachment zones because of the deployable joint arrangement. It is also observed that the temperature due to the severe aerodynamic heating effect is very high at the leading edge and increasing thickness zones at the joint. With increasing joint freeplay, the amplitude of the deformation response increases, indicating increased dynamic instability.

Three-dimensional flow structures and scalar mixing of a sand dune-inspired jet in crossflow

This paper performed particle image velocimetry (PIV) measurements and delayed detached-eddy simulations (DDES) to comprehensively investigate the flow and mixing behaviors of a sand dune(SD)-inspired JICF (jet in crossflow). PIV measurements were conducted in planes parallel to the mid-plane (Z/D = 0, 0.5, and 1), and three velocity ratios (VR = 0.4, 0.8, and 1.2) were studied. The time-averaged and turbulent flow features behind the sand dune-inspired JICF is strongly three-dimensional: the jet tends to move from the mid-plane to the outer planes and can stay attached well to the wall even at Z/D = 1. Then DDES method was applied to reveal detailed three-dimensional flow structures and mixing characteristics of the SD-inspired JICF, and a cylindrical JICF was also simulated as a benchmark for comparison. The horseshoe vortex, arch-shaped shear layer vortices, and streamwise rollers are mainly responsible for the formation of the anti-counter rotating vortex pair (anti-CRVP) observed in the mean flow field of SD configuration. Analysis of concentration distributions indicates that scalar mixing between the jet and the mainstream is highly correlated to the flow features and vortex structures, and the mixing strength of the sand dune-inspired JICF is generally weaker than that of the cylindrical JICF.

Analysis of the Complex Three-Dimensional Flow Structure in the Circulation Pump of the Flow-Making System Based on Delayed Detached Eddy Simulation

As the core component of the flow-making system, the circulating pump has differences in its internal flow structure under different operating conditions, which affects the flow quality of the environmental simulation test area and the authenticity of marine environmental simulation. To explore the internal flow characteristics and outlet evolution characteristics of the circulating pump, this paper uses the DDES (delayed detached eddy simulation) method for numerical simulation. This paper combines BVF (boundary vorticity flow) diagnosis and the limit streamline method to analyze the evolution characteristics of the unstable flow area on the blade surface; it uses the Q criterion to identify the vortex structure inside the pump and analyze its evolution and development laws. Additionally, a quantitative analysis of the flow state of the circulating pump using flow uniformity indexes is performed. The results show that the surface of impeller blades is uniform under 1.0 QN. At 0.7 QN, the evolution process of the blade suction surface BVF is periodic, with a corresponding period of about 2/9 T (0.02 s). At 1.0 QN, the strength and scale of the separated vortices inside the guide vanes are minimized compared to other flow rates, and the scale and strength of the vortices show a decreasing trend along the outer normal direction. The evolution period of the separation vortex on the pressure surface of the guide vane is about 1/3 T (0.033 s) under 1.1 QN and the evolution period of the suction surface of the guide vane is about 2/3 T (0.067 s) under 0.7 QN. The flow uniformity indexes value downstream of the pump outlet under 1.0 QN are very close to the ideal value; with a corresponding value of Ϛi = 0.023, θ¯ = 89.94°, γ = 0.95, λ = 97.9%, the outflow can be approximately regarded as axial uniform flow. The research results can provide theoretical support for the further optimization design of circulating pumps and lay the foundation for the implementation of real systems.

Modeling of wake features of a propeller using the vorticity confinement method

The instability and evolution mechanisms of propeller wakes are of vital significance to the development of next-generation propulsion devices with better hydrodynamic and noise performances. The temporal–spatial scales and the vortex details are important for the understanding of the vortex features and their dynamic responses to the propeller. In the present study, the vorticity confinement (VC) method was employed on the numerical simulations achieved by the improved delay detached eddy simulation with various advance coefficients to characterize the underlying features of wake flows. Comparisons were made between the results computed with and without the VC model from different perspectives. The analyses showed that the VC method captures more high-frequency power spectral density results as well as more small-scale vortical topology on the far downstream field based on the same spatial resolution and indicates the multi-scale interference on the tip vortex evolutionary trajectories. The VC method also elucidates rich small vortical structures with low advance coefficient and elliptical instability with high advance coefficient. This paper further widens our knowledge on the propeller wake evolution mechanisms and highlights the value of the VC method in the investigation of propeller wakes.

Numerical evaluation of wind direction effects on the turbulence aerodynamics of a ship airwake

The airwake characteristics around a ship body are an important consideration for helicopter pilots during shipboard operations, as airwake can lead to the formation of massively turbulent flow over the ship deck. Therefore, this study conducted a delayed detached eddy simulation (DDES) to investigate the impact of the bow part of the ship and the wind direction on the turbulent flow characteristics of the ship deck airwake. Numerical simulations were performed for two different ship models (1:12.5) of the Simple Frigate Shape 1 and 2 (SPF1 and SFS2) to analyze the influence of the bow part on the deck flow-field. Seven different orientations of wind direction angle (HW, RW15, RW30, RW45, RW60, RW75, and RW90) were numerically simulated for SFS1. The time-averaged velocity and pressure fields computed by the DDES approach were validated in comparison to those of the experimental data measured by the PIV data and Kulite pressure sensors, respectively, at various locations over the ship deck. The numerical data revealed that, while the deck flow-field is not influenced by the bow of the ship, the airwake flow is significantly affected by the wind direction angle. Specifically, as the wind direction angle is increased, the turbulent kinetic energy is also increased and the flow-field becomes more asymmetric. Moreover, the spectral analysis and time/space assessment of the flow field showed more pressure fluctuations and a higher level of unsteadiness over the ship deck with a larger wind direction angle, which are important parameters in shipboard operations.