Computational Fluid Dynamics Calculations Research Articles

Using radius of influence and adaptive collision mesh to capture droplet collision of a diesel engine

The collision of fuel droplets is a vital part of diesel engines. In this work, a three-dimensional (3D) model of diesel combustion in the cylinder of a diesel engine was constructed, and the radius of influence (ROI) and adaptive collision mesh (ACM) models were used to simulate the collision behavior of the droplets. For comparison, analysis was also conducted for when the droplet collision model was not used. The impacts of the ROI and ACM models were analyzed based on the engine operating conditions, and the relevant parameters of the ROI and ACM models were modified. It was found that if the ROI model was used with different influence radius, the average Sauter mean diameter (SMD) of the diesel droplets was affected. The ROI model had a larger impact on the computational fluid dynamics calculation time than the ACM model and a smaller impact on the engine power and pollutant emissions. A large number of parcels could be used to simulate diesel spray to reduce the dependence on grids. For simulations with more parcels, the efficiency of the ACM model was much higher than that of the ROI model.

Study on the Development of the Maneuvering Mathematical Model Considering the Large Angle Motion of Submarine

Maneuverability is a crucial factor for the safety and success of submarine missions. This paper introduces a mathematical model that considers the large drift and angle of attack motions of submarines. Various computational fluid dynamics (CFD) simulations were performed to adapt Karasuno's fishery vessel maneuvering mathematical model to submarines. The study also presents the procedure for obtaining the physics-based hydrodynamic coefficients proposed by Karasuno through CFD calculations. Based on these coefficients, the reconstructed forces and moments were compared with those obtained from CFD and to the hydrodynamic derivatives expressed by a Taylor expansion. The study also discusses the mathematical maneuvering model that accounts for the large drift angles and angles of attack of submarines. The comparison results showed that the proposed maneuvering mathematical model based on modified Karasno’s model could cover a large range of motions, including horizontal motion and vertical motions. In particular, the results show that the physics-based mathematical maneuvering model can represent the forces and moments acting on the submarine hull during large drift and angle of attack motions. The proposed mathematical model based on the Karasuno model could obtain more accurate results than the Taylor third-order approximation-based mathematical model in estimating the hydrodynamic forces acting on submarines during large drift and angle of attack motions.

Dynamic Structural Scaling Concept for a Delta Wing Wind Tunnel Configuration Using Additive Manufacturing

Considering aeroelastic effects plays a vital role in the aircraft design process. The construction of elastic wind tunnel models is a critical element in the investigation of occurring aeroelastic phenomena. However, the structural scaling between full-scale and reduced-scale configurations is a complex design and manufacturing task and is usually avoided in wind tunnel testing. This work proposes a numerical approach for a dynamic aeroelastic scaling technique, which is applied to a fictive delta wing configuration. This scaling methodology is designed to optimise the structural layout of wind tunnel models with an integrated rib and spar structure to meet the behaviour of a realistic full-scale equivalent. For the modelling approach of the wing structure, a beam and shell structure is utilised. The applied scaling laws for the relevant quantities and the applied procedures are described. Computational fluid dynamics (CFD) calculations are performed by solving the Reynolds-averaged Navier–Stokes (RANS) equations for the assumption of a rigid full-scale and down-scaled wing. These calculations are used to verify the aerodynamic scaling assumptions, which are applied to the scaling procedure of the wind tunnel model. Global aerodynamic coefficients are evaluated for a variety of angles of attack. The local flow phenomena of the full-scale and the scaled model are compared in more detail for a medium and a high angle of attack. The pressure coefficient distribution shows a proper accordance for the full-scale and the scaled model. To verify the results of the structural scaling optimisation, a high-fidelity structural full-scale model is compared with the scaled model using the ELFINI FEM solver. Therefore, all structural components are modelled by 2D elements. The results for the reduced eigenfrequencies and according modes of the full-scale and the scaled model show a high level of similarity. A static deformation of the structural grids is performed by applying the aerodynamic loads from the CFD simulations. The results show that the deviation of the nondimensional deformation between the scaled and the full-scale model is negligible. Consequently, the applied scaling methodology proves to be a valuable tool for the conceptual approach of designing aeroelastically scaled wind tunnel models considering 3D-printed material.

Aeroballistic optimization of long-range guided ammunition

PurposeThis paper aims to describe the use of optimization approaches to increase the range of near-future howitzer ammunition.Design/methodology/approachThe performance of a gliding projectile concept is assessed using an aeroballistic workflow, comprising aerodynamic characterization and flight trajectory computation. First, a single-objective optimization is run with genetic algorithms to find the maximal attainable range for this type of projectile. Then, a multi-objective formulation of the problem is proposed to consider the compromise between range and time of flight. Finally, the aerodynamic model used for the gliding ammunition is evaluated, in comparison with direct computational fluid dynamics (CFD) computations.FindingsApplying single-objective range maximization results in a great improvement of the reachable distance of the projectile, at the expense of the flight duration. Therefore, a multi-objective optimization is implemented in a second time, to search sets of parameters resulting in an optimal compromise between fire range and flight time. The resulting Pareto front can be directly interpreted and has the advantage of being useful for tactical decisions.Research limitations/implicationsThe main limitation of the work concerns the aerodynamic model of the gliding ammunition, which was initially proposed as an alternative to reduce significantly the computational cost of aerodynamic characterization and enable optimizations. When compared with direct CFD computations, this method appears to induce an overestimation of the range. This suggests future evolution to improve the accuracy of this approach.Originality/valueTo the best of the authors’ knowledge, this paper presents an original ammunition concept for howitzers, aiming at extending the range of fire by using lifting surfaces and guidance. In addition, optimization techniques are used to improve the range of such projectile configuration.

Computational fluid dynamics calculations in inferior turbinate surgery: a cohort study

PurposeTo investigate how the results of nasal computational fluid dynamics (CFD) simulations change due to inferior turbinate surgery and how the results correlate with patient specific subjective assessment and volumetric results in the nasal cavities.MethodsThe steady inspiratory airflow of 25 patients was studied pre- and postoperatively with heat transfer from the mucous membrane by performing CFD calculations to patient-specific nasal cone beam computed tomography images. These results were then compared to the severity of the patients’ nasal obstruction Visual Analogue Scale (VAS) and Glasgow Health Status Inventory assessments, and acoustic rhinometry measurements.ResultsTotal wall shear forces decreased statistically significantly (p < 0.01) in the operated parts of the inferior turbinates. Patients’ subjective nasal obstruction VAS assessment changes between the pre- and postoperative conditions correlated statistically significantly (p = 0.04) with the wall shear force results.ConclusionInferior turbinate surgery lead to decreased total wall shear force values postoperatively. Changes in subjective nasal obstruction VAS results against total wall shear force changes between the pre- and postoperative conditions were statistically significant. CFD data have a potential to be used for the evaluation of nasal airflow.

Investigation on the DNB-type critical heat flux in a fuel assembly with 5 by 5 rods

In this paper, Eulerian two-phase model coupled with wall boiling model was employed to simulate the departure from nucleate boiling (DNB) in a 5 × 5 fuel assembly. The numerical simulation accurately predicted the critical heat flux (CHF) and also its location. Compared with the calculated results from W-3 formula and FLICA subchannel code, the CFD (Computational Fluid Dynamics) calculations showed good agreement against experimental measurements with the deviation of 5%, but presented more detailed flow distribution. Based on CFD results, the method of CHF prediction was discussed with an eye on wall superheat, void fraction and vapor convective heat flux in rod surfaces. The distribution of flow field and liquid–vapor fraction affected by mixing vane were further studied. Mixing vane can continually influence the downstream thermal hydraulic characteristics, forming the diagonal circulation and square circulation with the flow development. As a result, the bubble aggregation firstly occurred on the surface of corner hot rod instead of central hot rod, which induced the local heat transfer crisis. The CFD calculations presenting the evolution process of physical parameters can provide guidance for rod bundle CHF test and fuel assembly design.

High-Fidelity Simulation of Mixing Phenomena in Large Enclosures

In the present work, two large eddy simulations (LESs) of single isothermal jets discharging into large enclosure facilities are proposed. The geometries and tested flow conditions correspond to scaled experiments of the upper plenum of high-temperature gas-cooled reactors. More specifically, two reference experiments were conducted at Texas A&M University and Michigan University. The objective of the present work is to validate these simulations with their corresponding reference experiments. The proposed LES models are performed with NekRS, a spectral element code with graphics processing unit capabilities developed at Argonne National Laboratory. These simulations were performed on the Summit supercomputer at Oak Ridge National Laboratory. For validation purposes, first- and second-order statistics from the computational fluid dynamics (CFD) calculation are compared with measurements obtained from the experiments. The models proved to be accurate, as these results are in good agreement. Additionally, flow visualization is provided showing that these models are able to retrieve similar effects to what are described in the literature for this type of flow configuration. Finally, the proposed models are part of a broader effort under the current Integrated Research Project of Nuclear Energy Advanced Modeling and Simulation 1.1, whose main objective is to deliver fast-running models to accurately predict complex physical phenomena, including for instance, turbulent mixing and thermal stratification. In this regard, the CFD models proposed here will be used to generate a high-fidelity data set to be applied in conjunction with data-driven methods to improve turbulence modeling closures.

Resistance reduction optimization of an amphibious transport vehicle

The resistance reduction optimal design of amphibious vehicles is essential to improve efficiency and reduce energy consumption. In this paper, the hydrodynamic characteristics of an amphibious transport vehicle are investigated by Computational Fluid Dynamics (CFD) method based on the Reynolds-averaged Navier-Stokes (RANS) solver. A set of towing tests are conducted to verify grid independence and computational accuracy. Four typical shape control parameters are selected as optimal design variables and the independent effects of each variable are analyzed. The sample set is obtained using Latin Hypercube Sampling (LHS), and corresponding three-dimensional models are generated based on the parameters of each sample point. CFD calculations are then used to obtain the resistance characteristics of the models. The Kriging method is utilized to establish an approximate model, and the credibility of the model is verified. The Non-Dominated Sorting Genetic Algorithm-II (NSGA-II) is used to find a global optimal solution or set based on approximate models. Two optimized configurations, Opt1 and Opt2, are obtained, corresponding to single- and multi-objective optimization results, respectively. At the design speed of the amphibious transport vehicle, Opt1 has the highest resistance reduction rate of 12.7907% under the full load condition, while Opt2 has resistance reduction rates of 11.0863% and 8.5293% with and without load, respectively.

Estimation of the wind drift factor and uncertainty analysis based on CFD computer simulations

PurposeThe purpose of this work is to present a procedure for determining the wind drift factor through two-dimensional computational fluid dynamics (CFD) simulations of the wind acting on a wavy sea surface, such that the subjectivity of its estimation is reduced.Design/methodology/approachThe wind drift factor was determined by two-dimensional CFD analyses with open-channel condition. The characteristic wave was determined by the Sverdrup–Munk–Bretschneider (SMB) method. The uncertainty analysis is based on convergence studies using a single parameter refinement (grid and time step).FindingsThis procedure allows the estimation of the wind drift factor in a fetch-limited domain. The domain's value in the analyzed region is 0.0519 ± 4.92% which is consistent with the upper values of the wind drift factors reported in the literature.Research limitations/implicationsThe use of a three-dimensional domain was impractical with the available computational resources because of the fine mesh required for wave modeling. The uncertainty analysis consisted only of a verification procedure. Validation against real data was not possible because of the lack of measured data in the analyzed region.Originality/valueThe wind drift factor is usually estimated based on either experience or random sampling. The original contribution of this work is the presentation of a CFD procedure for estimating the wind drift factor, in which the domain inlet is subjected to a wave boundary condition and to a wind velocity.

Computational Analysis, Three-Dimensional Simulation, and Optimization of Superfluid Stirling Cryocooler

Abstract The aim of this work is to analyze a superfluid Stirling cryocooler using superfluid helium as the working medium. The idea behind this kind of cryocooler is to utilize two conjoined Stirling coolers with a phase difference as to achieve heat transfer between them and thus negate the need for a regenerator. The two cycles exchange heat at an exchanger, referred to as a recuperator, placed where the regenerator would be typically. This apparatus is simulated through a 1D model where the full equations of state for the superfluid are being used, opposed to the common simplifications when modeling superfluids. This model provides the expected results for the initial case of 180 deg phase difference between the engines, and then finds the optimal phase difference for the best coefficient of performance. A 3D model is designed in the ansys fluent software, and the superfluid data are used in the computational fluid dynamics calculation. Running different cases, the optimal phase difference for the 3D case was found and compared to the 1D model. Additionally, the cryocooler was simulated to work in different frequencies for finding its optimal speed and deriving the cooling power to frequency plot.

Numerical Investigations of Water Column Responses at Different Moonpool Locations Within a Fixed Vessel

Abstract The oscillating water column (OWC) responses within forward, central, and aft located moonpools for a fixed rectangular vessel are studied numerically under regular head wave conditions using Reynolds-averaged Navier–Stokes-based computational fluid dynamics calculations. The free surface elevation of the confined water inside the moonpool for the piston mode frequencies is studied independently for the forward, central, and aft moonpools, showing a strong dependence on location, draft, and incident wave frequency. The relative response is largely magnified for wave frequencies around the resonant range. It is observed that the free surface response amplitude is significantly higher in the forward moonpool location, and the results are in well comparison with experiments performed in the towing tank. The variation of dynamic pressure and its influence on the moonpool responses is investigated to understand the position-specific fluctuations, which showed the presence of harmonics. The phase difference between the water column oscillations within the moonpool and the propagating wave in the domain depends on its position. Finally, the effect of the moonpool in modifying the pressure field is studied by comparison with a vessel without moonpool for a common incident wave frequency.

Multiobjective optimization of a staggered-rotor octocopter design based on a surrogate model

When designing a novel double-layer staggered-rotor octocopter with improved aerodynamic performance, the aerodynamic performance and structural parameters will have a complex coupling relationship that should be considered in the overall design process. A surrogate-model-based multiobjective optimization method is proposed in this study to optimize novel octocopter structural design schemes considering total thrust, the weight of the propeller and fuselage, the storage volume, and the fuselage volume. This approximation and optimization approach effectively reduces the cost of a large amount of computational fluid dynamics (CFD) calculations in octocopter design and provides a global prediction of octocopter performance. According to the verified optimal solution through CFD simulation, we can see that the surrogate model offers excellent predictive ability, and the prediction accuracy of thrust exceeds 95%. Compared with the initial optimum data, the optimal solution calculated from the optimization could generate 76.74% more thrust, the objective function y is improved by 11.48%, and the objective function a is improved by 322.06%. These results show that the aerodynamic/structural parameter optimization design method considering the influence of aerodynamic interference for multirotor aircraft proposed in this paper is feasible and exhibits good performance. The methodology proposed in this work could provide guidelines for structural parameter design optimization for double-deck multiple-rotor aircraft design at the preliminary design stage, as well as copter structural design considering multiple-rotor interference effects.

122 A New Dichotomic Personal Sampler for Semi-Volatile Aerosols Named “Ppas” for a Better Exposure Assessment of the Workers

Abstract Semi-volatile organic compounds (SVOCs) are airborne pollutants present as a mixture of airborne particles and their vapour. Evaluating the exposure of workers to SVOCs represents a major challenge to occupational hygienists due to different toxicological effects regarding the particles and the vapour phases on human health. Therefore, the exposure assessment requires sampling these phases separately. In this regard, several methods were proposed to separate the two phases. However, all these methods have biased measurements of the concentration of the particulate and vapour phases. As an alternative, we propose a new personal SVOCs sampler named PPAS for “Préleveur Personnel d’Aérosols Semi-volatils”. The PPAS was built on the virtual impactor concept but with an inverted ratio between the major and minor flow. The development of the PPAS was first carried out using computational fluid dynamics (CFD) and then using experiments to estimate the actual performances. A great attention was paid to reduce at their minimum the pressure drops between the inlet and the two exits to allow 8 hours samplings using personal pumps classically used for assessing the exposure of the workers in workplaces. The transmission efficiency η of the PPAS was evaluated by CFD calculations for particles size ranging between 0.05 and 20 µm and measured experimentally with mono-dispersed aerosols consisted of a mixture of glycerol and fluorescein particles of 0.15, 2, 3 and 4.5 µm. The aim of the presentation is to focus on the CFD and experimental tests that permit to develop the PPAS.

Numerical study on prediction and discrimination methods of propeller tip vortex cavitation inception

Tip vortex cavitation is typically the first type of cavitation in real ship propellers due to the scale effect. To lessen or eliminate propeller cavitation noise, it is necessary to effectively identify and predict the tip vortex cavitation initiation of the propeller and run the propeller as far as possible in the “non-cavitation area.” However, for the current numerical computation, it is impossible to determine the minimum pressure at the vortex core directly and correctly, making it difficult to anticipate the cavitation initiation of the propeller tip vortex. In this paper, based on computational fluid dynamics (CFD) numerical calculations and the tip vortex model proposed by Xin [Proceedings of 2013 Ship Hydrodynamics Conference (2013), pp. 211–218], we propose a new prediction method for propeller tip vortex cavitation initiation—“the tip vortex model method.” The propeller tip vortex is solved by CFD calculation in this model, and the minimum pressure at the downstream vortex core is examined based on the tip vortex model to determine the initiation of propeller cavitation. We examine the cavitation inception using the tip vortex model method and compare it to the results obtained using the minimum pressure coefficient method and the minimum vapor volume method. It is discovered that the cavitation inception number obtained by the tip vortex model method is closer to the experimental results. Furthermore, the effects of different turbulence models and grid settings on the prediction of tip vortex cavitation initiation are investigated, providing an effective reference for the prediction of propeller tip vortex cavitation initiation.

NUMERICAL INVESTIGATION OF PLATE COOLING USING MULTIPLE IMPINGING JETS IN DIFFERENT ALIGNMENTS

In this study, convective heat transfer by multiple impinging jet arrays in different arrangements is numerically investigated using Computational Fluid Dynamics (CFD). Computational domain consists of multiple jet array either in inline or staggered alignment and a target plate to be cooled by impinging jets. Distance between the jet array and the target plate is kept constant at H=28 mm. Diameter of circular jet nozzles is fixed at D=5 mm for all configurations. Effects of jet Reynolds number (Rej), spacing between circular jets and the alignment of the jet nozzles on aerothermal performance are parametrically investigated in the scope of this study. For staggered and inline alignments of the jet nozzles, Rej ranges from 5000 to 20000 and the ratio of the spacing to the jet diameter (s/D) changes between 2 and 6. CFD calculations are performed using finite volume based ANSYS-Fluent flow solver. Simulations are conducted for incompressible, steady and turbulent flow using k-ω SST turbulence model with ideal gas assumption for density and Sutherland law for viscosity. After intensive mesh convergence and validation tests, appropriate mesh resolution is determined and parametric investigations are performed. The study reveals that most dominant parameter for plate cooling is Rej followed by spacing between jets and finally jet alignment. For all Rej, inline jet nozzle alignment provides 15% higher average heat transfer rate than staggered alignment when s/D is close to the lower limit. However, it is shown that jet alignment does not affect thermal performance when s/D is higher.

Dynamic Thermal Neutron Radiography for Filling Process Analysis and CFD Model Validation of Visco-Dampers

The visco-damper is a crucial engine accessory from an operation- as well as vehicle-safety point of view. The service life of this damping product is determined by the degradation of the silicone oil applied to it. The thermal and mechanical degradation of the oil starts not at the first operation of the damper, but at the manufacturing stage when the oil is filled into the damper’s gap at high pressure. Finite volume method-based computational fluid dynamic calculations provide an opportunity to optimize the filling process by minimizing the oil degradation. A three-dimensional, transient, non-Newtonian, multiphase, coupled fluid dynamic and heat transfer simulation model was developed to analyse the filling process and to investigate the effect of the slide bearing’s cut-off position on the filling process. Dynamic thermal neutron radiography was employed to visualize the filling of a test damper for model validation from viscous and fluid dynamic aspects. Distinct properties of neutrons compared to the more commonly applied X-rays were proven to be an effective tool for real-time monitoring of the silicone oil’s front propagation in the damper’s gap and for quantifying the characteristics of the filling process. Visual matching and comparison of propagation times and oil front velocity profiles were used to validate the simulation results.

Construction and application of numerical diagram for high-skew propeller based on machine learning

The field of machine learning has experienced rapid growth, and it has introduced a new methodology for constructing propeller diagrams. To meet the high demand for designing high-skew propellers, a series of high-skew propeller schemes are generated, utilizing the INSEAN E1619 as the parent propeller. The Computational Fluid Dynamics (CFD) method was validated using the E1619 test results and was subsequently employed to perform virtual open water tests for all the series schemes. This effort produced 819 open water performance data of 42 propellers. The study trained and validated the traditional multivariate polynomial regression model and five conventional machine learning regression models based on the CFD calculation data. The analysis of the model prediction accuracy indicated that the Support Vector Machine (SVM) model had the least error among them for the digital expression of diagram hydrodynamic data. The prediction error of KT, KQ, and η decreased by over 20% compared to the LM model. The study subsequently developed a high-skew propeller diagram design program using the SVM regression model and applied it to a specific underwater vehicle's propeller design. The design results demonstrated that, compared to the B-series propeller, the design scheme provided by this numerical diagram had a comparable efficiency and a 6% smaller optimum diameter under unlimited diameter and a 7% higher efficiency under limited diameter for this case. Consequently, the developed numerical diagram in this paper provides a new tool for the propulsion performance evaluation and parameter selection of the propulsion system in the preliminary design stage for the high-skew propeller.

A Method for Predicting the Aeroelastic Response of Radial Turbomachines

AbstractAircraft intermittent combustion engines often incorporate turbochargers adapted from ground-based applications to improve their efficiency and performance. These turbochargers can operate at off-design conditions and experience blade failures brought on by aerodynamic-induced blade resonances. A reduced-order model of the aeroelastic response of general fluid–structural configurations is developed using the Euler–Lagrange equation informed by numerical data from uncoupled computational fluid dynamic (CFD) and computational structural dynamic calculations. The structural response is derived from a method of assumed-modes approach. The unsteady fluid response is described by a modified version of piston theory that approximates the local transient pressure fluctuation in conjunction with steady CFD solution data. The reduced-order model is first applied to a classical panel flutter scenario and found to predict a flutter boundary that compares favorably to the boundary identified by existing theory and experimental data. The model is then applied to the high-pressure turbine of a dual-stage turbocharger. The model predictions are shown to reliably determine the lack of turbine blade flutter and rudimentary damping comparisons are performed to assess the ability of the model to ascertain the susceptibility of the turbine to forced response. Obstacles associated with the current experimental state of the art that impinge upon further numerical validation are discussed.

An efficient method for helicopter fuselage shape optimization

PurposeThis paper aims to develop a new method of fuselage drag optimization that can obtain results faster than the conventional methods based on full computational fluid dynamics (CFD) calculations and can be used to improve the efficiency of preliminary design.Design/methodology/approachAn efficient method for helicopter fuselage shape optimization based on surrogate-based optimization is presented. Two numerical simulation methods are applied in different stages of optimization according to their relative advantages. The fast panel method is used to calculate the sample data to save calculation time for a large number of sample points. The initial solution is obtained by combining the Kriging surrogate model and the multi-island genetic algorithm. Then, the accuracy of the solution is determined by using the infill criteria based on CFD corrections. A parametric model of the fuselage is established by several characteristic sections and guiding curves.FindingsIt is demonstrated that this method can greatly reduce the calculation time while ensuring a high accuracy in the XH-59A helicopter example. The drag coefficient of the optimized fuselage is reduced by 13.3%. Because of the use of different calculation methods for samples, this novel method reduces the total calculation time by almost fourfold compared with full CFD calculations.Originality/valueTo the best of the authors’ knowledge, this is the first study to provide a novel method of fuselage drag optimization by combining different numerical simulation methods. Some suggestions on fuselage shape optimization are given for the XH-59A example.

Analysis of Surrogate Models for Vapour Transport and Distribution in a Hollow Fibre Membrane Humidifier

To achieve high efficiency and low degradation of a polymer electrolyte fuel cell (PEMFC), it is necessary to maintain an appropriate level of humidification in the fuel cell membrane. Thus, membrane humidifiers are typically used in PEMFC systems. Parameter studies are important to evaluate membrane humidifiers under various operating conditions to reduce the amount of physical tests. However, simulative studies are computationally expensive when using detailed models. To reduce the computational cost, surrogate models are set up. In our study, a 3D computational fluid dynamics (CFD) model of a hollow fibre membrane humidifier is presented and validated using measurement data. Based on the results of the validated CFD model, a surrogate model of the humidifier is constructed using proper orthogonal decomposition (POD) in combination with different interpolation methods. To evaluate the surrogate models, their results are compared against reference solutions from the CFD model. Our results show that a Halton design combined with a thin-plate-spline interpolation results in the most accurate surrogate humidifier model. Its normalised mean absolute error for 18 test points when predicting the water mass fraction in the membrane humidifier is 0.58%. Furthermore, it is demonstrated that the solutions of the POD model can be used to initialise CFD calculations and thus accelerate the calculation of steady state CFD solutions.