Modeling the Nonlinear Dynamic Roll of Generic Fighter Using Delayed Detached-Eddy Simulation

<div class="section abstract"><div class="htmlview paragraph">Among the many sources of uncertainty in an unsteady computational fluid dynamics (CFD) simulation, the statistical uncertainty in the mean value of a fluctuating quantity (for example, the drag coefficient) is of practical importance for vehicle design and development. This uncertainty can be reduced by extending the simulation run length, however, this increases the computational cost and leads to longer turnaround times. Moreover, it is desirable to be able to run an unsteady CFD simulation for the minimum amount of time necessary to reach an acceptable amount of uncertainty in the quantity of interest. This work assesses several methods for calculating the uncertainty in the mean of an unsteady signal. Simulated noise is used to validate the methods, and evaluation is carried out using signals from CFD simulations of realistic vehicle geometries. Calculating the uncertainty in the difference between two signals is also discussed. Finally, several methods are compared for estimating the stabilization (or “burn in”) time, which is present in the initialization of any unsteady CFD simulation.</div></div>

While designing the power requirements of a ship, the most important factor to be considered is the ship resistance, or the sea drag forces acting on the ship. It is important to have an estimate of the ship resistance while designing the propulsion system since the power required to overcome the sea drag forces contribute to ‘losses’ in the propulsion system. There are three main methods to calculate ship resistance: Statistical methods like the Holtrop-Mennen (HM) method, numerical analysis or CFD (Computational Fluid Dynamics) simulations, and model testing, i.e. scaled model tests in towing tanks. At the start of the design stage, when only basic ship parameters are available, only statistical models like the HM method can be used. Numerical analysis/ CFD simulations and model tests can be performed only when the complete 3D design of the ship is completed. The present paper aims at predicting the calm water ship resistance using CFD simulations, using the Flow-3D software package. A case study of a roll-on/roll-off passenger (RoPax) ferry was investigated. Ship resistance was calculated at various ship speeds. Since the mesh affects the results in any CFD simulation, multiple meshes were used to check the mesh sensitivity. The results from the simulations were compared with the estimate from the HM method. The results from simulations agreed well with the HM method for low ship speeds. The difference in the results was considerably high compared to the HM method for higher ship speeds. The capability of Flow-3D to perform ship resistance analysis was demonstrated.

The concept of an integrated rocket ramjet was initially introduced in the 1960s, leading to decades of research into dump combustor design [1]- [3] . The incoming air jets generate four corner vortices, while the dump section creates suction, collectively shaping the reactors. Therefore, the design of dump section is critical for a successful propulsion systems development. Parameters such as pressure drop, pressure fluctuations, and combustion efficiency must be evaluated across various flight regimes. Some of the known factors that affect overall ramjet engine performance include the size and efficiency of the reactors, dump effects, the dimensions of air intakes, angle, intake curvature, the flow separators in the intake flow stream, Reynolds number, and combustor dimensions [4]- [7] . The inherent inability to scale ramjet engine combustion chambers [8] poses a challenge when evaluating various geometrical configurations and operating points through experimentation. As a result, Computational Fluid Dynamics (CFD) becomes a crucial tool for advancing the development of ramjet propulsion engines. In this study, Large Eddy Simulation (LES) and Delayed Detached Eddy Simulation (DDES) techniques, coupled with the Steady Laminar Flamelet combustion model, are used to model a generic ramjet combustor which is introduced by Ristori et al. [9] . The experimental data used in context of the work is studied by many researchers to have more insight of combustion phenomenon in ramjet engine combustor [10], [11] . Grid convergence was ensured through the application of the Richardson extrapolation method [12] , and the grid quality was evaluated using the M-index defined by Pope [13] . A close agreement between both LES and DDES approaches, and experimental data was observed, confirming their accuracy in simulating the complex flow behaviour of the combustor. The findings reveal that both approaches provide good agreement with the experimental data regarding velocity profiles with only some minor discrepancies. However, a noteworthy distinction between DDES and LES is the behaviour of Turbulent Kinetic Energy and its distribution. The LES with WALE subgrid scale model tends to predict higher levels of Turbulent Kinetic Energy in the near-wall region compared to DDES, resulting in improved mixing and the formation of an early heated zone. This early combustion phase leads to a higher flow expansion and hence an increase in axial velocity, causing LES WALE to overestimate axial velocity at x=270 mm, whereas DDES predictions align slightly better with the experimental data. Both DDES and LES WALE simulations tend to overestimate combustion efficiency compared with measurements. However, the total pressure loss is well predicted by both approaches with only a discrepancy of lower than 0.3% compared to measured data that is well within the measurement error range. It's important to note that the overprediction of combustion efficiency remains an open issue, as discussed by other researchers also [11] . Future simulations could be extended to calculate heat loss to the walls what could be an explanation for the overprediction of combustion efficiency. The present research demonstrates that the Steady Laminar Flamelet model is capable of predicting flow structures in a ramjet combustor under reacting conditions. Within LES simulations, the prediction of turbulent kinetic energy within the near-wall region was enhanced, resulting in faster mixing and an overestimation of combustion efficiency. Even closer agreement with experimental data was achieved in DDES predictions, highlighting the effectiveness of employing eddy simulation with near-wall modeling when wall resolution is unfeasible. This approach not only demonstrates better CSP 118-2 agreement between DDES predictions and experimental data but also showcases its efficiency in reducing the need for excessively refined meshes in the study of dump-type low subsonic combustors.

The removal of toxic gases leaking during excavation in infrastructure projects is crucial for both human health and environmental protection. In this process, Computational Fluid Dynamics (CFD) simulations are highly valuable for modeling and analyzing complex physical processes associated with the transport and dispersion of gases. During infrastructure projects in geothermal regions, various gases may leak from underground sources. These gases may include toxic and/or flammable substances such as hydrogen sulfide (H₂S), carbon dioxide (CO₂), and methane (CH₄). Designing an effective ventilation system is essential for the removal of toxic gases through ventilation. CFD simulations can be utilized to evaluate the design and performance of ventilation systems. Modeling gas leaks from sources encountered during excavation using CFD simulations can help understand how gases move throughout infrastructure projects and their environmental impacts. CFD simulations can assist in optimizing factors such as the placement of ventilation systems, duct design, air flow rates, and filtration efficiency. This optimization ensures the effective removal of toxic gases and minimizes environmental impacts. CFD simulations can also be used to assess the efficiency and safety of ventilation systems designed for the mitigation of toxic gases. Additionally, simulating the operation of ventilation systems during potential emergency situations can help in evaluating associated risks.

This numerical study investigates the 3-D flow field and aerodynamic characteristics of DU 00-W-212 wind turbine airfoil at high Reynolds numbers. The Computational Fluid Dynamics (CFD) simulations are performed at Reynolds number of 3 million at three different angles of attack for the pre-stall, stall, and post-stall conditions, by using an open source CFD solver SU2. The Delayed Detached Eddy Simulations (DDES) with the Spalart-Allmaras (SA) turbulence model and Langtry-Menter (LM) transition model are performed to address the challenge of predicting unsteady flow characteristics with transition, particularly on the suction side of the airfoil. The 3-D DDES with SA results with and without LM transition model are compared with the 2-D RANS with SA simulations and available experimental data.

In the development of bio-inspired Micro Air Vehicles (MAVs), flapping-wing configurations derived from natural fliers such as honeybees offer unique advantages in maneuverability and stability within complex environments. However, modeling the unsteady aerodynamic behavior of flapping wings is computationally intensive. In this study, a simplified quasi-steady approach is adopted by simulating the aerodynamics of a rigid, honeybee-inspired drone at multiple static orientations using a virtual inflow rotation technique. Computational Fluid Dynamics (CFD) simulations are performed at various effective angles of attack by altering the direction of the incoming flow while keeping the wing geometry fixed. Key vortex structures, including leading-edge and wingtip vortices, are analyzed to evaluate their role in lift and thrust generation. Aerodynamic forces (lift, drag, and thrust) are quantified across multiple static orientations to gain insights into aerodynamic performance. In parallel, a basic static structural analysis of the rigid wing is conducted using the aerodynamic pressure loads obtained from the CFD simulations. The structural response under representative aerodynamic loads is evaluated to assess stress distribution and potential wing deformation. This combined aerodynamic and structural analysis provides a comprehensive understanding of wing performance and structural integrity, offering valuable data for optimizing bio-mimetic MAV design.

Bench test and computational fluid dynamics (CFD ) simulation of the air pump loss on the 380 hydraulic retarder are completed in this paper . It turns out that the CFD simulation has nice reliability from the contrast of the air pump loss between the test and the simulation . And on this foundation , CFD simulation of two kinds of retarders with different turbulent structures is done . The contrast of the results of the simulation give the effects of different turbulent structures on cutting down the are pump loss .

Computational fluid dynamic (CFD) simulations in support of the SHARP-B2 (Slender Hypervelocity Aerothermodynamic Research Probes) program are presented. Pre-flight simulations of the aerothermal flight environment have been made to aid in the design of the flight hardware and instrumentation. Simulations of a critical flight qualification ground test performed in the 20 MW Panel Test Facility (PTF) arc jet, which is equipped with a semi-elliptical nozzle, have also been performed. The arc jet simulations were performed with the same CFD code that is used in the flight calculations. For both the flight and the arc jet simulations, the CFD results are used to provide surface heat transfer coefficients that serve as boundary conditions for an in-depth conduction thermal response code. By using the same CFD tool to compute the aerothermal environments for both the ground test and the flight test environment, useful comparisons are made regarding the traceability of the ground test environment to flight. Introduction The NASA Ames Research Center has been developing new Ultra High Temperature Ceramics (UHTC's) with the goal that these materials will enable sharp leading edges to be used for future space vehicles. Because of their unique thermo-structural properties, these materials are capable of operation at temperatures near 5100 °F without ablation. The materials have been developed and tested in ground-based arc jet facilities, and a flight test program designated SHARP (Slender Hypervelocity Aerothermodynamic Research Probes) has been initiated. The first flight demonstration, SHARP-B1, incorporated a UHTC nosetip mounted on a U.S. Air Force Mkl2A entry vehicle in collaboration with Sandia National Laboratory (SNL), and was successfully flown in May, 1997. The second flight test, SHARP-B2, which incorporated four instrumented UHTC strakes mounted on the side of the entry vehicle, was flown in September 2000. The goal of these flight tests is to assess the performance of the materials under entry conditions. The use of Computational Fluid Dynamic (CFD) simulations for the design of Thermal Protection Systems (TPS) has evolved to an extent that they have been integrated into the preliminary design process of Reusable Launch Vehicle (RLV) programs such as the X-33. Real-gas CFD simulations with finite-rate chemistry and proper boundary conditions for coupling with material thermal response codes are now routinely performed on high-end laboratory workstations. Much of the ground based testing of advanced TPS components is done in arc-heated test facilities such as those located in the Arc Jet Complex at the NASA Ames Research Center. These facilities are capable of simulating the high enthalpy flow environment experienced by entry vehicles for a broad range of test conditions and configurations. Semi-elliptical nozzles are available for the testing of flat panels in a high enthalpy boundary layer environment. CFD is • Aerospace Engineer, Reacting Flow Environments Branch, Member AIAA. t Senior Research Scientist, ELORET, Member AIAA. Copyright © 2001 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Title 17, U.S. Code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental Purposes. All other rights are reserved by the copyright owner. (c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.

Today, many wells in heterogeneous carbonate reservoirs throughout the Middle East and Caspian Sea area are being completed with long intervals and complex completion equipment, such as limited entry liners and inflow control devices (ICDs). Accurate modeling and understanding of fluid placement during a stimulation operation through such long complex completions can be quite challenging. In this paper, an integrated approach of modeling, experiments and computational fluid dynamics (CFD) simulations will be presented. A computational tool based on a transient one-dimensional (1D) approach has been developed in-house to model stimulation through such completions. In order to validate the 1D approach for reliable fluid displacement predictions, annulus fluid displacement experiments in perforated liners supported by CFD simulations have been conducted. The experimental setup consists of an outer Lucite pipe representing the well-bore geometry and an inner aluminum pipe with multiple perforations of variable diameter. The setup mimics the real field application in a 1:1 scale with respect to the pipe and perforation diameters while the test section is limited to 27 ft. The experimental procedure is as follows: fluid is pumped into the annulus through the perforations until the annulus is completely filled,the fluid tank is switched "on-the-fly" to the tank with the displacing fluid resulting in the displacement of the annulus fluid by the displacing fluid through the perforations. The experiments and the CFD simulations indicate that even with a single open perforation inside the 27-ft test section, the three-dimensional (3D) flow field around the perforation rapidly transitions to uniform annular flow within a few feet uniformly displacing the annulus fluid. The model also provides insight into various well injection processes in sandstone and carbonate formation, such as scale squeezes, solvent treatments, and HF acid treatments. Introduction The length of production and injection intervals in a single well continues to increase in order to contact more reservoir rock with a single wellbore penetration and improve project economics. Multiple, thick stacked reservoirs are accessed by vertical and deviated wells while thinner reservoirs are being exploited with longer and longer horizontal wells1–3. To keep up with drilling capability, completion technology has advanced considerably in the past few years. Horizontal wells are "compartmentalized" using mechanical and/or swellable packers. Within a given compartment, injection and production can be controlled by use of inflow control devices (ICDs), limited entry (LE) liners, and/or sliding sleeves. The liners also make it easier to enter the completion interval with logging tools, wire line, and coiled tubing. While various tools are available to evaluate long-term, steady-state production and injection into such wells, modeling of short-term, transient injection into such completions is very challenging due to the long lateral lengths, limited entry points from the liner to each compartment, and the presence of an open annulus with occasional packer isolations. This is especially important for long wells in carbonate formations as all wells require acid stimulation upon initial completion, and occasionally throughout the well life.

A normally-open thermally-actuated microvalve was designed (using microfabrication/soft-lithography techniques involving 3D Printed molds), assembled and tested. The motivation of the research work is to develop an array of microvalves for precise delivery of water to individual plants in a field (with the goal of developing smart irrigation systems for high value cash-crops in the agricultural sector). It is currently impossible to control application of irrigation-water at the level of a single plant. If such a capability were practically available on farms, the result would be a step change in precision agriculture, such that the output of every plant in a farm field could be optimized (i.e., food-water-energy nexus in sustainability applications). The aim of this study is to develop and test a microfluidic system (consisting of a microvalve array) that could be controlled, capillary by capillary, to deliver the needed amount of water to individual plants in a large field. Two types of test fluids were leveraged for thermo-hydraulic actuation of the microvalves developed in this study: (a) Design-I: using air, and (b) Design-II: using Phase Change Material (PCM). The PCM used in this study is PureTemp29. The proposed approach enabled a simple and cheap design for microvalves that can be manufactured easily and are robust to weather conditions (e.g., when exposed to the elements in orchards and open fields). Other advantages include: safe and reliable operation; low power consumption; can tolerate anomalous pressure loads/fluctuations; simple actuation; affords easy control schemes; is amenable for remote control; provides long-term reliability (life-cycle duration estimated to be 3∼5 years); can be mass produced and is low maintenance (possibly requiring no maintenance over the life time of operation). The microvalve consists of two layers: a flow layer and a control layer. The control layer is heated from below and contains a microfluidic chamber with a flexible polymeric thin-membrane (200 microns in thickness) on top. The device is microfabricated from Poly-Di-Methyl-Siloxane (PDMS) using soft lithography techniques (using a 3D Printed mold). The control chamber contains either air (thermo-pneumatic actuation) or PCM (thermo-hydraulic actuation involving repeated melting/freezing of PCM). The flow layer contains the flow channel (inlet and outlet ports, horizontal section and valve seat). The experimental results from testing the efficacy of the two types of micro-valves show a 60% reduction (for thermo-pneumatic actuation using air) and 40% reduction (for thermo-hydraulic actuation using PCM) in water flow rates for similar actuation conditions (i.e., heater temperature values). PCM design is expected to consume less power (lower OPEX) for long-term actuation but may have slower actuation speed and have higher manufacturing costs (CAPEX). Air actuation design is expected to consume more power (higher OPEX) for longer-term operation but may have faster actuation speeds and lower manufacturing costs (CAPEX). Computational Fluid Dynamics (CFD) simulations were performed to investigate the effect of flowing water (in the microfluidic channel) on the average absolute pressure and temperature of air in the actuation chamber. The CFD simulations were performed using a commercial tool (Ansys™ 2019R1®). The results from the CFD simulations are presented in this study.

The actual cooling load of underground stations in recent years has been much lower than the designed load thirty years ago. Therefore, it is important to estimate the actual load in the planning of cooling systems. In this study, the cooling load caused by train wind in an underground station was discussed and a field measurement and computational fluid dynamics (CFD) simulation were conducted. The main conclusions are as follows: (1) The measurement showed that air volume of the train wind was greatly affected by the train speed and the tunnel structure (single or double track). (2) In the CFD simulation, the train was modeled as a moving body to simulate train wind. The CFD simulation with a pressure loss model in the tunnel could reproduce the measurement. (3) The influence of train wind on the platform cooling system was examined by the CFD simulation in terms of an influence coefficient. In the Shin-Nihombashi station, the influence coefficient was approximately 0.38 in the area connecting to the tunnel while the coefficient was about 0.24 in the center area.

In this paper, it will be shown that small inlet fins mounted in the compressor inlet pipe can improve the compressor stability limit by alleviating the impeller inlet recirculation flow. Performance tests on the hot gas test bench and unsteady Computational Fluid Dynamics (CFD) simulations were conducted to investigate the mechanisms for surge condition improvement. The stability limit was shifted to lower mass flow rates in the low Mach number region by inlet fins in performance test results. As the compressor rotational speed increased, the stability limit shifted to high mass flow rates (kink characteristic) at a certain pressure ratio. The stability limit was unaffected by inlet fins in the high Mach number region after the kink point. Therefore, it was considered that the factors responsible for triggering surge were different near the kink point. It is thought that the instability of the diffuser does not occur after impeller stall in the low speeds region, but that diffuser stall occurs in the high speeds region causing the kink characteristics. Flow patterns extracted from unsteady CFD at the near surge point determined from the performance tests are analyzed to investigate the difference of surge pattern between low and high Mach number region. In low Mach number region, inlet fins suppress the extension of high entropy flow upstream of the impeller. It is assumed that the high entropy region was recirculation flow attributable to impeller stall. In addition, there are differences in the behavior on compressor characteristics with and without inlet fins. The positive slopes of compressor’s pressure ratio to flow rate become gentle by suppressing the development of pre-swirl (better surge characteristic). In the high Mach number region, flow patterns and compressor characteristics are almost the same in both cases. It is considered that the diffuser stall occurred first, and the diffuser stall triggered surge before impeller stall developed toward upstream. Therefore, the inlet fins did not work sufficiently since there was no recirculation flow from impeller.

Modern aeroengine designers face the challenge of reducing fuel consumption, which is pushing compressor technology into new design spaces. To optimize these design spaces, high-fidelity computational models are crucial to the compressor design process. It is important to validate these models with experimental data. Nonintrusive measurement techniques allow for the acquisition of data well suited for this comparison, as they do not lead to local disruptions of the flow field. This investigation utilized three-component laser Doppler velocimetry to acquire a unique dataset of detailed unsteady velocity measurements in the vaned diffuser of an aeroengine centrifugal compressor. These measurements allowed for a thorough study of the flow development in the vaneless and semivaneless space of the diffuser as well as through the diffuser passage. The components of the Reynolds stress tensor were also determined at multiple locations in the diffuser flow field. These data are used to study the jet and wake propagation from the impeller exit flow field into the diffuser passage and the resulting secondary flow structures. Predictions from unsteady computational fluid dynamics (CFD) simulations using the shear stress transport (SST) and baseline k–ω explicit algebraic Reynolds stress model (BSL-EARSM) turbulence models are also compared with these experimental data. Both turbulence models yielded results that qualitatively agreed with the experimental radial velocity profile through the vaneless and semivaneless space. With the experimentally determined Reynolds stress tensor, the turbulent kinetic energy (TKE) is calculated at multiple points through the flow field and is compared to the TKE at the same geometric locations in the computational flow field. This comparison highlights the difference in dissipation and production of turbulence between the experimental data and the computational predictions. Investigating the differences in TKE throughout the diffuser helps elucidate the differences in predicted flow structures in the diffuser passage.

The synthetic array technique has previously been used to provide insight for developing improved microphone array data processing techniques. In recent work, however, it has also been successfully applied to diagnose the source of unexpected (and nonphysical) tones which arose in unsteady computational fluid dynamics (CFD) simulations of hot supersonic jets. The insight obtained from this method has allowed the authors to rapidly arrive at a strategy that greatly improves the results. This success opens up additional areas where the synthetic array technique can find application.

Speeding up CFD simulation of fluidized bed reactor for MTO by coupling CRE model