High-fidelity Computational Fluid Dynamics Simulations Research Articles

Surrogate-based aerodynamic shape optimization of a morphing wing considering a wide Mach-number range

Aerodynamic shape design considering both subsonic and hypersonic performance is a challenge in the field of aerospace. Many studies have shown that morphing wing is a promising technology to address this challenge. In this article, a new morphing mechanism which changes both the plane shape (such as span and sweep angle) and the profile (such as chord length and relative thickness) of the wing is proposed and a multi-objective optimization design for this new morphing mechanism is conducted based on surrogate-based optimization (SBO) algorithm. In the optimization design, three different configurations of the morphing wing which are the 36-, 45- and 70-degree sweep angle state, respectively and four different flow conditions which are subsonic flow (0.25 Ma), transonic flow (0.85 Ma), supersonic flow (1.2 Ma) and hypersonic flow (6 Ma) are considered. 36-degree sweep angle state is used for subsonic flow, 45-degree sweep angle state is used for transonic flow and supersonic flow and 70-degree sweep angle state is used for hypersonic flow. Subsonic lift and transonic, supersonic, hypersonic lift-to-drag ratios are objectives of this optimization design which has up to 64 design variables. To reduce computational cost of high-fidelity CFD (computational fluid dynamics) simulations and find the global optimum, Kriging surrogate model combined with a parallel infill-sampling method and a multi-round strategy are employed in this study. At last, the optimized morphing wing is evaluated and compared with the baseline and a fixed wing which is a moderate sweep wing. Results show that the optimized morphing wing features a very good aerodynamic performance improvement over the flow regimes from subsonic to hypersonic flow conditions.

High-Fidelity Computational Analysis on the Noise of a Side-by-Side Hybrid VTOL Aircraft

This paper investigates the acoustics of a side-by-side urban air mobility (UAM) aircraft with 0%, 5%, 15%, and 25% rotor overlaps in forward flight based on high-fidelity computational fluid dynamics (CFD) simulations. The CFD and acoustics simulations are carried out using the HPCMP CREATETM -AV rotorcraft simulation and analysis tool Helios and the acoustic prediction tool PSU-WOPWOP. First, the influence of the finest wake-grid spacing (Δfinest) on the side-by-side rotor acoustics is studied. No significant difference in overall sound pressure level (OASPL) is found between the two wakegrid spacing cases: Δfinest = 5% Ctip and 10% Ctip. Physical noise sources, such as impulsive self blade–vortex interactions, rotor-to-rotor blade–vortex interactions, and separated flow and blade interactions, are investigated in details based on high-fidelity CFD simulation results and noise-integrand analyses. The effect of rotor overlap on rotor acoustics is also assessed. It is found that the maximum OASPL difference among the overlap cases is about 1 dB, but the radiation patterns are different for each overlap case. Furthermore, the noise of the side-by-side rotor with 0% and 25% overlaps is compared against the noise of a conventional helicopter and various background noises. The side-by-side rotor noise is comparable with the helicopter noise around 1000 Hz. The results also show that the side-by-side rotor noise could not be fully masked by the freeway background noise even at an altitude of 1500 ftand exceed Uber's noise guideline of 62 dBA at 500 ft. Thus, noise reduction technology should be pursued to lower UAM aircraft noise, which is one of major technical barriers for UAM public acceptance.

Power augmentation of Darrieus wind turbine blades using trapped vortex cavity

Enhancing the performance of Darrieus Vertical Axis Wind Turbines (VAWTs) is the key to boost their possible commercialisation in the yet highly competitive wind energy market. This study evaluates an active boundary layer control technique to increase the aerodynamic efficiency of Darrieus VAWTs. A cavity is created on the airfoil's suction side, where suction is applied to create a trapped vortex. High-fidelity Computational Fluid Dynamics (CFD) simulations are used after validation against experimental results. The effect of suction momentum ratio Cμ on the performance of the turbine is investigated. The turbine with suction cavity airfoils (SC) shows a higher power coefficient than the one with baseline airfoil (BL) blades, especially at low tip-speed ratios. For the selected test case, the net maximum predicted power coefficient is 0.435 for the SC turbine at TSR = 2.3, 0.375 for the baseline at TSR = 2.6. At the lower tip-speed ratios, i.e. TSR = 2, the power coefficient of the SC turbine is almost double that of the BL turbine. The feasibility of the active control technique is finally discussed, demonstrating its potential as an effective solution for the performance augmentation of the Darrieus turbine.

Multifidelity Heating Prediction of Adaptable, Deployable Entry Placement Technology Vehicles

The objective of this work was to investigate a multifidelity modeling approach to accurately and efficiently predict the laminar convective, turbulent convective, and radiative heating on adaptable, deployable entry placement technology vehicles in Mars entry. A previously developed cokriging-based multifidelity modeling approach was used to model the heat fluxes at several surface locations along the vehicle, including the rib sections. The laminar convective heat flux multifidelity model was found to have a mean convective heat rate error of approximately 3% when compared with high-fidelity computational fluid dynamics (CFD) simulations. The turbulent convective heat flux multifidelity model was found to have a mean convective heat rate error of approximately 8% when compared with high-fidelity CFD simulations. The radiative heat flux multifidelity model was found to have a mean convective heat rate error of approximately 10% when compared with high-fidelity CFD simulations. Compared with a single-fidelity model, the multifidelity model required, at most, one-third the number of high-fidelity model evaluations to obtain the same accuracy level. The computational cost of evaluating the multifidelity model was approximately six orders of magnitude less than one high-fidelity model simulation.

Characterization of the Ejector Pump Performance for the Assisted Bidirectional Glenn Procedure

This study introduces an algebraic model informed by computational fluid dynamics (CFD) simulations to investigate the performance of the assisted bidirectional Glenn (ABG) operation on a broad range of conditions. The performance of this operation, as measured by the superior vena cava (SVC) pressure, depends on the nozzle area in its ejector pump and the patient’s pulmonary vascular resistance (PVR). Using the developed algebraic model to explore this two-dimensional parameter space shows that the ejector pump can create a pressure difference between the pulmonary artery and the SVC as high as 5 mmHg. The lowest SVC pressure is produced at a nozzle area that decreases linearly with the PVR such that, at PVR =4.2 (Wood units-m2), there is no added benefit in utilizing the ejector pump effect (optimal nozzle area is zero, corresponding to the bidirectional Glenn circulation). At PVR =2 (Wood units-m2), the SVC pressure can be lowered to less than 4 mmHg by using an optimal nozzle area of ≈2.5 mm2. Regardless of the PVR, adding a 2 mm2 nozzle to the baseline bidirectional Glenn boosts the oxygen saturation and delivery by at least 15%. The SVC pressure for that 2 mm2 nozzle remains below 14 mmHg for all PVRs less than 7 Wood units-m2. The mechanical efficiency of the optimal designs consistently remains below 30%, indicating the potential for improvement in the future. A good agreement is observed between the algebraic model and high-fidelity CFD simulations.

Power module heat sink design optimization with ensembles of data-driven polynomial chaos surrogate models

We consider the problem of optimizing the design of a heat sink used for cooling an insulated gate bipolar transistor (IGBT) power module. The thermal behavior of the heat sink is originally estimated using a high-fidelity computational fluid dynamics (CFD) simulation, which renders numerical optimization too computationally demanding. To enable optimization studies, we substitute the CFD simulation model with an inexpensive polynomial surrogate model that approximates the relation between the device’s design features and a relevant thermal quantity of interest. The surrogate model of choice is a data-driven polynomial chaos expansion (DD-PCE), which learns the aforementioned relation by means of polynomial regression. Advantages of the DD-PCE include its applicability in small-data regimes and its easily adaptable model structure. To address the issue of model-form uncertainty and model robustness in view of limited training and test data, ensembles of DD-PCEs are generated based on data re-shuffling. Then, using the full ensemble of surrogate models, the surrogate-based predictions are accompanied by uncertainty metrics such as mean value and variance. Once trained and tested in terms of accuracy and robustness, the ensemble of DD-PCE surrogates replaces the high-fidelity simulation model in optimization algorithms aiming to identify heat sink designs that optimize the thermal behavior of the IGBT under geometrical and operational constraints. Optimized heat sink designs are obtained for a computational cost much smaller than utilizing the original model in the optimization procedure. Due to ensemble modeling, the optimization results can also be assessed in terms of uncertainty and robustness. Comparisons against alternative surrogate modeling techniques illustrate why the DD-PCE should be preferred in the considered setting.

Implementation of a coupled simulation framework with neural network and Modelica for fast building energy simulation considering non-uniform indoor environment

The coupling of computational fluid dynamics (CFD) and building energy simulation (BES) program enables the simultaneous consideration of the indoor environment quality and building energy performance in architecture design. Meanwhile, it improves the energy simulation accuracy for non-uniform indoor environments as compared to a standalone BES. However, a CFD-BES coupled simulation confronts a great challenge in that conducting high-fidelity CFD simulations is time-consuming, making it impractical for scenarios requiring a large number of CFD executions. In this study, an innovative coupled simulation framework is proposed and implemented for fast energy simulation considering non-uniform indoor environments. As a surrogate for CFD, a neural network (NN) for achieving a fast and accurate prediction of the indoor air distribution is coupled with a Modelica-based energy simulation program. The crucial functionality of the coupled simulation framework is validated against the results of a coupled simulation between fast fluid dynamics (FFD) and Modelica. Furthermore, the framework is tested with a more complicated case to explore its feasibility and potential for practical applications. Compared to a standalone BES, the coupled simulation considering a non-uniform environment demonstrates more reasonable results regarding heat transfer calculations and system operations. Moreover, the proposed framework requires only 52 s to execute a simulation with a physical process of 24 h, resulting in an approximately 94% reduction in calculation time relative to a coupled simulation between CFD and BES.

Efficient reduced-order aerodynamic modeling in low-Reynolds-number incompressible flows

This study aims to develop a non-intrusive reduced-order aerodynamic modeling framework for agile motion across a broad operating range in low-Reynolds-number incompressible flows. Since most previous reduced-order models are only valid in the neighborhood of the operating point, large amounts of high-fidelity input-output data have to be generated to cover the interested operating range, which requires expensive computational resources. To tackle such an issue, a signal interpolation approach by combining the discrete empirical interpolation method (DEIM) with Kriging technique is proposed to approximate the aerodynamic responses to a prescribed linear ramp-step maneuver with remarkable accuracy, instead of performing computational fluid dynamics (CFD) simulation at each operating point. The interpolated input-output data can be used to establish low-dimensional state-space aerodynamic models, by identifying the stability derivatives first and subsequently capturing the remaining transient dynamics via the eigensystem realization algorithm (ERA). To demonstrate the proposed framework, unsteady lift coefficients of a two-dimensional flat plate pitching about the leading edge are investigated over the range with Reynolds numbers 100∼500 and base angles of attack 0∼10 deg. Numerical results show good agreement between the reduced-order models and high-fidelity CFD simulations.

Impact of roof geometry on cross-ventilation in vaulted buildings: a CFD study

The roof geometry is an important parameter in determining the natural cross-ventilation in buildings. Although many studies have been performed on natural ventilation, the impact of the large set of vaulted roofs on the building cross-ventilation remains to be addressed. In this paper, high-fidelity computational fluid dynamics (CFD) simulations, validated with experimental data, are performed on five naturally ventilated buildings with two opposing windows, each with a specific type of vaulted roof and otherwise identical, in 0° incident flow angle, to assess the impact of vaulted roof geometry on the building cross-ventilation performance. The following vault geometries are investigated and compared against a flat-roof building with the same specifications: (i) segmental, (ii) low-rise pointed, (iii) mid-rise catenary (iv) high-rise pointed and (v) high-rise catenary. The results show that compared to the flat-roof building, the vaulted roofs cause a <5% decrease in volume flow rate and 16-29% increase in the average mean velocity magnitude at the occupants’ level. In vaulted buildings, the low-velocity regions of the flow are moved further away from the occupied zone towards the ceiling, thus providing a fresher air to the occupants. The results clarify the high potential of vaulted roofs for natural ventilation and sustainable design.

Impact of volume distribution on pedestrian wind environment in high-rise urban districts: a CFD study

Pedestrian wind environment assessment is becoming an essential part of the urban design process especially in dense urban areas due to its ability to address the wind comfort/safety/health concerns in an early phase. In this paper, high-fidelity computational fluid dynamics (CFD) simulations, validated with experimental data, are performed on eight different designs in a generic urban layout to study the impact of volume distribution on pedestrian wind environment in high-rise urban districts. The results show that the blockage effects of the high-rise buildings decelerates the wind in the streets parallel to the flow while accelerating the flow in the streets perpendicular to the flow. This effect is evident up to a two block distance upstream of the high-rises. Furthermore, it is shown that consequent rows of high-rises in the downstream of the first row facing the wind flow have little effect on the upstream pedestrian wind; however, they have a significant role in the extent of affected areas downstream. The findings of this study provide further understanding about the impact of different volume distributions on pedestrian wind environment in high-rise urban districts and clarify their effect on wind safety and comfort.

Numerical investigation of the direct liquid cooling of a fast-charging lithium-ion battery pack in hydrofluoroether

• A novel battery direct liquid cooling system with HFE-6120 is investigated numerically. • A partial height channel design is proposed to promote the pack energy density. • A multilayer structure and cross-flowing configuration are introduced to improve the battery temperature uniformity. • The cooling capacity map of direct liquid cooling is obtained to guide the system design. Battery thermal management systems are critically important for ensuring the safety and prolonging the lifetime of lithium-ion batteries in electrical vehicles, especially those under fast charging. In this paper, a novel direct liquid battery cooling system based on a hydrofluoroether (HFE-6120) coolant is proposed for fast-charging battery packs. This paper numerically investigates the critical parameters in direct liquid cooling (DLC) with high-fidelity computational fluid dynamics (CFD) simulations. The results show that the DLC with a full-size channel design and high flow velocity control has a redundant cooling performance with the problems of low energy density and high power consumption, which can be resolved through optimization. First, when designed with a partial height channel and controlled with an appropriate coolant velocity, the mass energy density can be improved by up to 20.3% and the power consumption can be reduced by 95.3% compared to the selected baseline. Second, the maximum temperature difference and temperature standard deviation can be reduced by 18.1% and 25.0%, respectively, with a multilayer structure and cross-flowing configuration. These findings establish an improved understanding of the key parameters of DLC systems and provide guidelines for the design of direct liquid battery cooling.

Peregrine Falcon’s Dive: Pullout Maneuver and Flight Control Through Wing Morphing

During the pullout maneuver, peregrine falcons were observed to adopt a succession of specific flight configurations that are thought to offer an aerodynamic advantage over aerial prey. Analysis of the flight trajectory of a falcon in a controlled environment shows it experiencing load factors up to , and further predictions suggest this could be increased up to almost during high-speed pullout. This can be attributed to the high maneuverability promoted by lift-generating vortical structures over the wing. Wind-tunnel experiments on life-sized models in the different configurations together with high-fidelity computational fluid dynamics simulations (large-eddy simulations) show that deploying the hand wing in a pullout creates extra vortex lift, which is similar to that of combat aircraft with delta wings. The aerodynamic forces and the position of the aerodynamic center were calculated from the simulations of the flow around the different configurations. This allowed for an analysis of the longitudinal static stability in the early pullout phase, confirming that the falcon is flying unstably in pitch with a positive slope in the pitching moment and a trim angle of attack of about 5 deg, which is possibly to maximize responsiveness. The hand wings/primaries were seen to contribute to the augmented stability, acting as “elevons” would on a tailless blended-wing/body aircraft.

Design and aerodynamic evaluation of a medium short takeoff and landing tactical transport aircraft

The present article deals with the conceptual design of a new medium short takeoff and landing tactical transport aircraft, which is intended to expand the institutional capabilities of the Colombian Air Force in terms of versatility and flexibility. An original design strategy was developed during the conceptual design, combining classical methodologies and high-fidelity computational fluid dynamics (CFD) simulations. This methodology allowed the aircraft to be assessed in a single design space, based on its design requirements, mission, and applicable airworthiness standards. Once obtained a baseline concept, the aerodynamic study focused on the flow around two types of wingtip devices: tip tanks and blended winglets. These devices were designed to optimize the performance capabilities of the aircraft, while keeping simple certification procedures. Wind tunnel experiments and CFD simulations were carried out to evaluate and select the best configuration. Lift, drag, and pitching moment coefficient charts, along with vorticity contours, are presented. Results showed that blended winglets have a significant potential for improving aircraft performance without severe structural weight penalties, allowing additional payload capabilities and/or increased range and fuel savings. Finally, the optimized aircraft is compared to major competitors in order to discuss and highlight its main advantages and feasibility for future production.

Multifidelity Turbulent Heating Prediction of Hypersonic Inflatable Aerodynamic Decelerators with Surface Scalloping

The objective of this work was to investigate a multifidelity modeling approach to accurately and efficiently predict the turbulent convective heating on hypersonic inflatable aerodynamic decelerators with both smooth and scalloped walls. A previously developed co-kriging-based multifidelity modeling approach was used to model the turbulent and laminar convective heat fluxes on smooth wall vehicles. The smooth wall turbulent and laminar multifidelity heating models were then combined to create a multifidelity model of the augmented turbulent heat flux on scalloped vehicles. The smooth wall turbulent heat-flux multifidelity model was found to have a mean convective heat rate error of approximately 7% when compared to high-fidelity computational fluid dynamics (CFD) simulations. The scalloped augmented turbulent heat-flux multifidelity model was found to have a mean convective heat rate error of approximately 10% when compared to high-fidelity CFD simulations. Compared to a single-fidelity model, the multifidelity model required approximately one-quarter the number of high-fidelity model evaluations to obtain the same accuracy level. The computational cost of evaluating the multifidelity model was approximately five orders of magnitude less than one high-fidelity model simulation.

High-fidelity CFD simulations of two wind turbines in arrays using nonlinear frequency domain solution method

Aerodynamics of a wind turbine within windfarms is strongly influenced by the wake of neighbouring turbines. In particular, the performance of a wind turbine can be dramatically reduced depending on its location in the wake region of an upstream turbine. A detailed investigation of the effect of the upstream turbine on the downstream turbine with respect to their distances is essential for the design and optimisation of wind farm layouts. Conventional time domain solution methods, such as Unsteady Reynolds Averaged Navier Stokes (URANS) based Computational Fluid Dynamics (CFD) model of wind turbines in arrays, can provide a detailed analysis of this interaction effect. These methods are, however, impractical due to a high computational cost required for modelling turbines in array configurations. In this paper, a novel modelling and computational method is proposed to simulate two wind turbines in arrays by considering them as a multi-stage turbine. A nonlinear frequency domain solution method is then employed to model flow nonlinearities due to their interactions. The distances between the turbines are varied, and the effects of the upstream wind turbine on the downstream one are thoroughly investigated. Extensive validations of the nonlinear frequency domain solution method against the conventional time domain solution method reveal that the proposed frequency domain solution method provides accurate results while reducing the computational cost by one to two orders of magnitude.

A Case Study on Pathogen Transport, Deposition, Evaporation and Transmission: Linking High-Fidelity Computational Fluid Dynamics Simulations to Probability of Infection

A high-fidelity, low-Mach computational fluid dynamics simulation tool that includes evaporating droplets and variable-density turbulent flow coupling is well-suited to ascertain transmission probability and supports risk mitigation methods development for airborne infectious diseases such as COVID-19. A multi-physics large-eddy simulation-based paradigm is used to explore droplet and aerosol pathogen transport from a synthetic cough emanating from a kneeling humanoid. For an outdoor configuration that mimics the recent open-space social distance strategy of San Francisco, maximum primary droplet deposition distances are shown to approach 8.1 m in a moderate wind configuration with the aerosol plume transported in excess of 15 m. In quiescent conditions, the aerosol plume extends to approximately 4 m before the emanating pulsed jet becomes neutrally buoyant. A dose–response model, which is based on previous SARS coronavirus (SARS-CoV) data, is exercised on the high-fidelity aerosol transport database to establish relative risk at eighteen virtual receptor probe locations.

A CFD data-driven aerodynamic model for fast and precise prediction of flapping aerodynamics in various flight velocities

Abstract

Innovative Box-Wing Aircraft: Emissions and Climate Change

The PARSIFAL project (Prandtlplane ARchitecture for the Sustainable Improvement of Future AirpLanes) aims to promote an innovative box-wing aircraft: the PrandtlPlane. Aircraft developed adopting this configuration are expected to achieve a payload capability higher than common single aisle analogues (e.g., Airbus 320 and Boeing 737 families), without any increase in the overall dimensions. We estimated the exhaust emissions from the PrandtlPlane and compared the corresponding impacts to those of a conventional reference aircraft, in terms of Global Warming Potential (GWP) and Global Temperature Potential (GTP), on two time-horizons and accounted for regional sensitivity. We considered carbon dioxide, carbonaceous and sulphate aerosols, nitrogen oxides and related ozone production, methane degradation and nitrate aerosols formation, contrails, and contrail cirrus. Overall, the introduction of the PrandtlPlane is expected to bring a considerable reduction of climate change in all the source regions considered, on both the time-horizons examined. Moreover, fuel consumption is expected to be reduced by 20%, as confirmed through high-fidelity Computational Fluid Dynamics (CFD) simulations. Sensitivity of data, models, and metrics are detailed. Impact reduction and mitigation strategies are discussed, as well as the gaps to be addressed in order to develop a comprehensive Life Cycle Assessment on aircraft emissions.

Artificial Neural Networks based wake model for power prediction of wind farm

In the wind industry, power prediction of wind farm is commonly implemented by analytical wake models, which is low-cost but insufficient in accuracy for high-turbulent wake modelling. In this study, a novel machine-learning-based wake model is developed to improve the power prediction of wind farms. The presented model can reproduce the velocity and turbulence fields in turbine wakes commensurate to the high-fidelity Computational Fluid Dynamics (CFD) simulations while achieving good computational efficiency. Driven by massive CFD simulation dataset, the implicit relationship between inflows and wake flows is established using the Artificial Neural Networks (ANN) technique based on back-propagation algorithm. The reduced-order method Actuator Disk Model with Rotation (ADM-R) and modified k−ε turbulence model are implemented into RANS simulations to save the computational costs dramatically in producing the big-data of wake flows. The ANN wake model is deployed in the Horn Rev wind farm, and validated against LES, onsite measurement, and analytical wake models. The conclusions show that the ANN model can appreciably improve the power predictions compared with the existing analytical models and match the LES and measurement data well. The validated model is also adopted to investigate the influence of wind direction and turbine layout on power production of wind farms.

Aeromechanical Analysis of a Complete Wind Turbine Using Nonlinear Frequency Domain Solution Method

Abstract The high-fidelity computational fluid dynamics (CFD) simulations of a complete wind turbine model usually require significant computational resources. It will require much more resources if the fluid–structure interactions (FSIs) between the blade and the flow are considered, and it has been the major challenge in the industry. The aeromechanical analysis of a complete wind turbine model using a high-fidelity CFD method is discussed in this paper. The distinctiveness of this paper is the application of the nonlinear frequency domain solution method to analyze the forced response and flutter instability of the blade as well as to investigate the unsteady flow field across the wind turbine rotor and the tower. This method also enables the aeromechanical simulations of wind turbines for various interblade phase angles in a combination with a phase shift solution method. Extensive validations of the nonlinear frequency domain solution method against the conventional time domain solution method reveal that the proposed frequency domain solution method can reduce the computational cost by one to two orders of magnitude.