In-house Solver Research Articles

Numerical investigation of breaking waves impact on vertical breakwater with impermeable and porous foundation

Three different types of breaking waves impact on a vertical breakwater with impermeable and porous foundations are studied using our in-house solver, DUTFOAM. The numerical model is based on the Volume-Averaged Reynolds-Averaged Navier-Stokes (VARANS) method and the numerical results are compared with experimental data to obtain a reasonable agreement. The characteristics of flow fields inside and outside the porous region under different breaking wave conditions are discussed and compared. When considering the impermeable foundation, breaking waves that entrapped small air pockets pose the most extensive pressure and forces, while the broken waves exerted the minimum. The porous foundation, with varying porosity values, dramatically affects the flow field and resulting structural forces. Our findings demonstrate that more considerable peak pressures and higher acting positions with porous foundations than impermeable situations for all three breaking wave conditions. Moreover, a sharp increase in horizontal forces and overturning moments occurs in broken wave conditions when the porosity equals 0.5, which poses a threat to stability and deserves additional attention.

Multi-physics simulation of 3D in-flight ice-shedding

In-flight ice accretion may possibly jeopardize the safety of fixed- and rotary-wing aircraft. Icing can possibly occur if supercooled water droplets in clouds impinge on the aircraft surfaces and freeze upon impact. It may result in instrument failures and degradation of the aerodynamic performances. A major problem related to ice accretion is the possibility of ice shedding from the main body and impacting other parts of the aircraft or being ingested by the engines. In fixed-wing aircraft, shedding is caused by the action of the aerodynamic forces or the activation of an Ice Protection System. In the present work, a multi-physics framework is presented to simulate ice accretion and shedding from wings and engine nacelles. The aerodynamics is computed using the open-source toolkit SU2 (Economon et al., 2015)[1] . Cloud droplet trajectories are computed using the arbitrary-precision Lagrangian in-house solver PoliDrop. Then, the in-house ice accretion toolkit PoliMIce (Gori et al., 2015) is used to determine the ice layer. An algebraic level-set approach with iterative volume mesh refinement has been developed to extract the ice shape from the iced wing geometry. A FEM structural analysis is performed on the accreted ice shape by means of the open-source code MoFEM (Kaczmarczyk et al., 2014, 2020) [2]. Internal stresses within the ice geometry due to aerodynamic forces are computed. Three-dimensional ice accretion simulations are performed to check the validity of the present approach.

Analytical and Numerical Solutions for Three-Dimensional Granular Collapses

This research paper presents a comprehensive approach to investigating dry granular collapses in three dimensions, by combining analytical, numerical, and experimental methods. The experimental investigation utilised a novel apparatus to study granular collapses in the laboratory. It is demonstrated that a quasistatic understanding of granular collapses can accurately predict the final normalised run-out distances for dynamic granular collapses. Our approach involved establishing a correlation between the angle of repose and the initial aspect ratio of the granular column. It is also shown that the material point method (MPM) is suitable for modelling granular collapses in three dimensions. Our in-house solver was further validated using experimental evidence under an explicit formulation, resulting in good agreement between the numerical and experimental results. The findings demonstrate the effectiveness of our in-house solver for three-dimensional granular collapse modelling.

Real-time model for wave attenuation using active plate breakwater based on deep reinforcement learning

This paper presents a numerical study of the interaction between irregular waves and actively controlled plate breakwater based on deep reinforcement learning (DRL), in which wave attenuation performance is mainly discussed. A numerical wave flume (NWF) is built and an in-house solver is developed to integrate CFD and DRL. Validations on wave generation and interaction between incident waves and the plate are carried out. An NWF-DRL coupled model is proposed to simulate the actively controlled plate moving to attenuate waves, where the motion of the plate is controlled by DRL. It is shown that under the regular wave and trichromatic wave group, both the trained agents can obviously reduce the wave height compared to that under fixed plate. Moreover, the further trained agents can reduce the transmitted wave heights to a significantly low level in the three more complex and unknown irregular wave cases. Meanwhile, the model does a great job of preventing the development of focused wave height in an irregular wave train. This research first examines the wave attenuation of a DRL-controlled breakwater in irregular wave environments, which may offer fresh perspectives on wave attenuation and even the design of intelligent marine equipment.

Numerical Investigation on the Thermal Protection Characteristics of a New Active Jet Design Parameter for Hypersonic Flight Vehicle

This study investigated the thermal protection performance of an active jet thermal protection system (PRsAJ-TPS) based on a new jet design parameter PRs for hypersonic flight vehicles (HFVs). The new parameter PRs is defined as the relationship between the jet flow total pressure and the free flow total pressure behind the outer bow shock. A 20° tilted nozzle design is employed together with the PRs to form the PRsAJ-TPS. Theoretical and numerical analysis is performed to prove the advantages of using the PRs. A conventional in-house CFD solver with the k ‐ ω SST turbulence model is utilized to perform the calculation. The influence of different PRs (working in the short penetration mode) and flight angles of attack on the performance of the PRsAJ-TPS is also studied. The simulation results confirmed that with a constant PRs, the Mach disk location stays the same and the normalized heat flux reduction is similar at different flight conditions. Nearly linear relationships exist between the new design parameter PRs and thermal protection performance indicators. The PRsAJ-TPS also exhibits good protection when flight angle of attack (AoA) varies between 0° and 40°, with the best results achieved at AoA = 0 ° . This study provides valuable information for the engineering application of the jet-based TPS to future HFVs.

Three-dimensional flow simulation and cavitation erosion modeling for the assessment of incubation time and erosion rate

A compressible three-dimensional in-house flow solver is employed for the assessment of cavitation erosion. The flow solution method provides the wall load, which is coupled to a one-dimensional ductile material model and which yields the incubation time and erosion rate. Due to the assumption of a homogeneous mixture in the flow solver, details of collapsing wall adjacent single bubbles cannot be resolved, so that two different wall load models are presented. In the first method, a collapse detection algorithm based on the mass flux divergence is applied, load collectives are statistically evaluated by the multitude of detected collapses, and a spectrum of distinct loads is passed on to the material model. Since the physical simulation time is much shorter than the real exposure time, a method for the time extrapolation of the wall load to capture realistic time scales is presented. In the second method, a sub grid scale micro jet model is applied, and the wall load is approximated by mean values, so that a time extrapolation is dispensable. Both methods require calibration to e.g. experimentally measured incubation time. An application to the widely used Grenoble axisymmetric impinging jet test case reveals, that the first method fails to capture the location of maximum wear. Due to the inclusion of an erosion probability for the detection of prospectively erosive collapse events in the second method, a good match with data is obtained. Beyond a validation for a broad range of erosive flow conditions, the use of alternative material models including high cycle fatigue as important wear mechanism is planned in future studies.

A coupled Eulerian interface capturing and Lagrangian particle method for multiscale simulation

A new Eulerian–Lagrangian coupling on a staggered fluid mesh is proposed to simulate multiscale atomization. This coupling relies on a sharp interface capturing method (ICM) to transport the resolved fluid structures and a Lagrangian tracking algorithm to model the under-resolved Eulerian droplets. The Lagrangian droplets momentum is spread to the source terms of the incompressible fluid momentum equations through a spatial filtering operation, and the flow velocity around the Lagrangian droplets is corrected to account for their local flow disturbance. This allows accurate transport of Lagrangian droplets that are both smaller and larger than the fluid mesh spacing. The implementation of the algorithm for switching from and to Eulerian toward Lagrangian framework is discussed, along with criteria validating a transformation. Then the Eulerian–Lagrangian coupling is applied to several test cases from the literature, and is compared to our in-house pure ICM solver on the atomization of a liquid jet. The results show that the Eulerian–Lagrangian coupling improves the physical analysis of the atomization, and achieves more accurate results for poorly resolved droplets.

Insulation behavior of foamed based geopolymer as a thermally efficient sustainable blocks

The importance of sustainability and energy efficiency in the construction and design of houses is crucial in today's environment. The material used as an insulation layer within the building envelope restricts heat transfer through it. However, heat transfer depends upon the characteristics of the insulating layers and their properties. Therefore, creating materials that possess low thermal conductivity while maintaining their mechanical, physical and durability properties is of utmost significance. The aim of this research is to explore the feasibility of utilizing foamed insulating geopolymer blocks as a means to address energy efficiency and environmental sustainability issues. The research involves utilizing copper slag and glass powder as the primary raw materials to produce the geopolymer. Additionally, the technique of foaming is applied to enhance the thermal resistance of the resulting product. The study results revealed that the foamed geopolymer material exhibited thermal conductivity in the range of 0.13 to 0.16 W/mK. Also, the developed product was subjected to conjugate thermal analysis to understand the heat transfer behavior of material. The heat transfer analysis is performed by in-house developed conjugate heat transfer solver in OpenFOAM. The variation of temperature through the solid geopolymer walls to internal room environment is reported, and Nusselt number at the solid–fluid interface is plotted to observe the insulation strength of developed geopolymer. The findings suggest the developed product can provide better thermal insulation than conventional material, in addition to this the foamed geopolymer can be treated as sustainable material as it utilizes waste and reduces the energy requirements of buildings.

Effects of combustion on the near-wall turbulence and performance for supersonic hydrogen film cooling using large eddy simulation

Supersonic film cooling using fuel on board is an effective way to simultaneously shield the huge heat and momentum flux transported from the mainstream to the wall in a scramjet engine. The self-ignition and combustion of the injected fuel film will significantly change the turbulent transport behavior in the boundary layer. To reveal the effects of the boundary layer combustion on the near-wall turbulence and wall fluxes, large eddy simulations (LES) of the Burrows–Kurkov supersonic combustion experiment using hydrogen as a film are performed based on the in-house solver scramjetFoam. The solver successfully captures the additional skin friction reduction phenomenon induced by the boundary layer combustion compared to other numerical works using LES in the public literature. The results reveal that further increased anisotropy of turbulence combined with the low-density region contributes to a remarkable suppression of turbulent transport processes in the wall-normal direction. The self-ignition point of the hydrogen film is found to oscillate back and forth in a span of 80 mm, which significantly enhances turbulence in the boundary layer. However, the increased turbulent fluctuating velocity is mainly concentrated in the streamwise direction, while the other two components are suppressed instead. The findings are also essential for improving engineering computations based on the Reynolds averaged simulation method.

Local Inverse Mapping Implicit Hole-Cutting Method for Structured Cartesian Overset Grid Assembly

An automatic hole-cutting method is proposed to search donor cells between a structured Cartesian mesh and an overlapping body-fitted mesh. The main flow is simulated on the structured Cartesian mesh and the viscous flow near the solid boundary is simulated on the body-fitted mesh. Through the spatial interpolation of flux, the surface boundary information on the body-fitted mesh is transferred to the Cartesian mesh nodes near the surface. Cartesian mesh box near a body-fitted mesh cell is selected as a local inverse map. The Cartesian nodes located inside the donor cells are marked by the relative coordinate transformation, so that all Cartesian nodes can be classified and the hole boundaries are implicitly cut. This hole-cutting process for overset grid assembly is called Local Inverse Mapping (LIM) method. In the LIM method, spatial interpolation of flux is carried out synchronously with the marking of Cartesian nodes. The LIM method is combined with the in-house finite-difference solver to simulate the unsteady flow field of moving bodies. The numerical results show that the LIM method can accurately mark the Cartesian hole boundary nodes, the search efficiency of donor cells is high, and the result of spatial interpolation is accurate. The calculation time of overset grid assembly (OGA) can be less than 3% of the total simulation time.

Numerical modeling of shaped charge jet penetration into ceramic–metal double-layered medium using smoothed particle hydrodynamics

The prediction of the damage effects of shaped charge projectile to ceramic–metal multi-layered target is a challenging task to address. In this paper, the smoothed particle hydrodynamics (SPH) method is applied to simulate the penetration of the metal jet generated by the shaped charge detonation into ceramic–metal double-layered plates. The presented SPH model incorporates different equations of states. Moreover, the elastic-perfectly plastic constitutive model and the Johnson–Holmquist-II material constitutive model were employed for modeling the mechanical behaviors of the solid materials in this study. Firstly, simulation of the high velocity impact process of a ceramic ball on a ceramic–metal double-layered plate was conducted to validate the presented constitutive model. After the validation of the numerical model, simulations of penetration of a shaped charge into a double-layered ceramic–metal plate by using millions of SPH particles were conducted. The simulation results (perforation diameter and debris cloud) are in good agreement with the available experimental data, which shows that our in-house SPH solver is capable of tackling the shaped charge detonation and its penetration into multi-layered structures very well. Furthermore, the presented SPH model can reproduce different types of fracture patterns observed in experiments and their dynamic formation processes.

Using vortex generators for flow separation control on tidal turbine profiles and blades

Tidal energy can play an important role in the Net Zero transition. Increasing tidal turbine performance through innovation is crucial if the cost of tidal energy is to become competitive compared to other sources of energy. The present investigation is a proof-of-concept study for the application of Vortex Generators (VGs) on tidal turbines in view of increasing their performance. The more mature wind energy industry uses passive VGs either as a retrofit or in the blade design process to reduce separation at the inboard part of wind turbine blades. Tidal turbine blades also experience flow separation and here we examine whether passive vane VGs can be used to reduce or suppress that separated flow. First, a wind tunnel investigation is performed to assess the performance of VGs on a 20% thick profile from the blade. Then, the VG effect on the 2D-profile is modelled in a Reynolds Averaged Navier-Stokes in-house solver. Results show that low profile VGs, i.e. VGs shorter than the local boundary layer, can increase the performance of the blade profile and successfully reduce flow separation. The VG effect on blade performance is examined in model scale and in full-size. VGs successfully suppress separation in both cases and it is shown that full-size information should be used for the placement of VGs. A maximum power coefficient increase of 1.05% is observed at a tip speed ratio of λ=3. The present proof-of-concept study demonstrates for the first time the potential of passive VGs to be included either in the design process of a tidal turbine blade or as a retrofit solution.

An investigation into the effects of damaged compartment on turning maneuvers using the free-running CFD method

It is necessary to maintain certain maneuverability to perform missions or return to port for a damaged ship. In this work, the free-running turning maneuvers of a surface combatant with a damaged bow compartment are simulated numerically using an in-house unsteady RANS solver, coupled with the dynamic overset approach. The effects of damaged compartment on the turning capability are evaluated by several turning circle simulations of the ship with different initial floating/loading conditions and closed damaged opening. The numerical method is verified by grid/time-step convergence studies with free-running turning maneuvers, and the results have good matches with the benchmark data. The maneuvering parameters of the damaged ship towards the port side are compared against those of the intact ship, in which smaller turning circle as well as larger roll, pitch and heave motions are found in the damaged condition. The ship's initial conditions are adjusted to investigate the effects of changed heel, trim angles and increased displacement on the turning behavior of the damaged ship. It is proved that initial heel/trim angles have great impacts on the turning maneuvering but the increased displacement shows minor effects. The ingress and egress of floodwater will cause smaller turning indices.

Computation of drag crisis of a circular cylinder using Hybrid RANS-LES and URANS models

Numerical simulation of flow past a circular cylinder across the “drag-crisis” region is extremely challenging for turbulence models because the boundary layer undergoes laminar–turbulent transition and variable-locus separation. We investigate the SA-DDES hybrid model along with two variants, namely, SA-kLES and SA-ILES, based on Spalart–Allmaras (SA) model, and include for comparison the SA-BCM transition and the SA-URANS models, for Re ranging from 50,000 to 5 million, using an in-house unstructured grid solver. All hybrid RANS-LES models produced clearly turbulent-like behavior, as evident from the Q-criterion, while the URANS models did not. A decline in the drag coefficient is noticed in all the turbulence models, but not the sharp decrease observed experimentally, with one exception: the SA-BCM transition model, which predicted the drag coefficients much closer to the experiments. The hybrid RANS-LES models outperformed the URANS SA-BCM model only in the fully turbulent trans-critical region and better represent the physics in the wake region for all Reynolds numbers studied. All the hybrid RANS-LES models produced similar results, suggesting comparatively equal performance in predicting separated flows. We believe that the performance of a hybrid model for mid-range Reynolds numbers will be greatly enhanced if the model is equipped to handle the laminar–turbulent transition.

Hydrodynamic optimization of pump-turbine runner

The paper suggests the approach to automatic CFD-based optimization of the pump-turbine runner. An in-house 3D flow solver CADRUN is used for the solution of steady-state RANS equations and evaluation of objective functions in representative operating points of turbine and pump operating regimes. Both efficiency and cavitation characteristics are taken into account. Two approaches have been considered, resulting in 4- and 3-objective shape optimization problems. These problems were solved using multi-objective genetic algorithm. It was shown that the obtained optimized runners feature increased efficiency both in turbine and pump mode with cavitation performance, similar to that of the initial runner.

Flow-mediated interaction between a forced-oscillating cylinder and an elastically mounted cylinder in less regular regimes

This study investigates the interaction between an actively oscillating cylinder and a passive cylinder elastically mounted with a damper. Both cylinders are rigid, immersed in a viscous fluid, of the same diameter and constrained to move along the two cylinders' centerline. This problem is simulated by an in-house finite-element solver. Six non-dimensional groups are chosen as input: the active cylinder's frequency f1/fn=0.05−3.2 and amplitude A1/D=0.159−1.432, the passive cylinder's damping ratio ζ=0, 0.02 and mass ratio m*=2, the Reynolds number Rem=35−315, and gap distance G/D=2.5. The resulting Keulegan–Carpenter and the Stokes numbers are KC=1−9 and β=35. In total, 2176 combinations are studied in this parametric space. An increase in KC leads to higher irregularity and larger vibration amplitude of the passive cylinder. In regime C, the passive cylinder vibrates in a pulse-beating pattern due to the periodic switching of the streaming direction. In regime E, the passive cylinder responds with intermittent irregularity. In regime F, the flow structure switches intermittently among unrecognizable irregularities and three regular patterns resembling those observed in regimes C and E. In regime G, the flow is highly irregular and circular, where vortices shed from consecutive cycles can merge, forming a much larger one.

Comparison of large eddy simulations against measurements from the Lillgrund offshore wind farm

Abstract. Numerical simulation tools such as large eddy simulations (LESs) have been extensively used in recent years to simulate and analyze turbine–wake interactions within large wind farms. However, to ensure the reliability of the performance and accuracy of such numerical solvers, validation against field measurements is essential. To this end, a measurement campaign is carried out at the Lillgrund offshore wind farm to gather data for the validation of an in-house LES solver. Flow field data are collected from the farm using three long-range WindScanners, along with turbine performance and load measurements from individual turbines. Turbulent inflow conditions are reconstructed from an existing precursor database using a scaling-and-shifting approach in an optimization framework, proposed so that the generated inflow statistics match the measurements. Thus, five different simulation cases are setup, corresponding to five different inflow conditions at the Lillgrund wind farm. Operation of the 48 Siemens 2.3 MW turbines from the Lillgrund wind farm is parameterized in the flow domain using an aeroelastic actuator sector model (AASM). Time-series turbine performance metrics from the simulated cases are compared against field measurements to evaluate the accuracy of the optimization framework, turbine model, and flow solver. In general, results from the numerical solver exhibited a good comparison in terms of the trends in power production, turbine loading, and wake recovery. For four out of the five simulated cases, the total wind farm power error was found to be below 5 %. However, when comparing individual turbine power production, statistical significant errors were observed for 16 % to 84 % of the turbines across the simulated cases, with larger errors being associated with wind directions resulting in configurations with aligned turbines. While the compared flapwise loads in general show a reasonable agreement, errors greater than 100 % were also present in some cases. Larger errors in the wake recovery in the far wake region behind the lidar installed turbines were also observed. An analysis of the observed errors reveals the need for an improved controller implementation, improvement in representing meso-scale effects, and possibly a finer simulation grid for capturing the smaller scales of wake turbulence.

Analytical modelling of ship bottom grounding considering combined surge and heave motions

This paper provides a new contribution to the analytical treatment of ship grounding accidents. New formulations are proposed to assess the resisting force of outer/inner bottom plating and transverse floors when the vessel undergoes combined surge and heave motions during the grounding event. Considering shallow and sharp rocks described by parabolic functions, analytical solutions are derived from plastic limit analysis and validated by comparison to non-linear finite element simulations. A failure criterion is also proposed to trigger the rupture of the bottom plating and all the derived closed-form expressions are implemented into an in-house solver. The solver is then coupled to a 6-DOFs external dynamics program, which allows to account for the action of the surrounding water. Resulting tool is first validated on a full scale cruise ship by comparison to finite element results. It appears than although some discrepancies arise, especially in the response of transverse floors after rupture, the bottom damage distribution seems to be well predicted. Finally, the developed tool is used to quickly predict the grounding response of different types of ships and the influence of their mass and hydrodynamic properties on the damage extent is investigated.

Three-dimensional study on the interaction between a container ship and freak waves in beam sea

Freak wave occurs unexpectedly in the ocean with an extreme wave crest and focused wave energy, resulting in many marine accidents. The interaction between a container ship and freak waves in beam sea is studied in this paper to better understand the influence of freak waves on ships. A three-dimensional in-house solver is developed and validated for the freak wave generation and the wave-ship interaction. Characteristics of the interaction process, motion responses of the ship and the green water loadings induced by the freak waves are obtained and analyzed. Comparisons are carried out to reveal the influences of the freak wave crest and sequence on the roll, heave and impact pressures. Relations between motion responses of the ship and the green water event are discussed. Influences of ship speeds on the wave-ship interaction are addressed.

A study on the effect of driver section length on the flow field inside a two-dimensional closed-ended viscous shock tube: A numerical investigation

The interaction of a reflected shock wave with the boundary layer inside a closed-ended shock tube is studied by many researchers using different numerical schemes. However, the interaction of a reflected shock wave having a decaying pressure profile ahead of the reflected shock is lacking in the literature. It is essential to quantify the deviation in flow characteristics experienced in tests performed inside the shock tube compared to field tests while studying blast wave attenuation and mitigation. In the present study, the effect of transient upstream pressure on the shock wave reflecting from a solid wall and the associated flow separation inside the boundary layer is examined in detail through numerical simulations using the viscous shock tube problem for Re = 1000. Simulations were performed using an in-house 13th-order high-resolution hybrid solver with 50 million grid points. The transient pressure profile behind the incident shock wave is achieved by varying the non-dimensional driver section length from 0.5 to 0.02 while keeping the overall shock tube length as 1. The flow field is scrutinized through numerical schlieren and vorticity plots. It is observed that the decaying pressure profiles behind the incident shock wave have an immense impact on the dynamics of shockwave-boundary layer interaction and the vortices emanating from the shear layer due to Kelvin–Helmholtz Instability. The secondary vortices inside the boundary layer, vortices at the shear layer, and compression waves in the separated boundary layer region reduce with a decrease in driver section length. The triple point height increases as driver section length decreases due to the weakening of upstream velocity. The Kelvin–Helmholtz vortices originating from the triple point moves back into the separated boundary layer rather than interacting with the end wall. It suggests that the decaying pressure behind the incident shock wave minimizes the secondary effects on the solid wall during shock wave impingement.