High Fidelity CFD Model Research Articles

Numerical investigation and reduced order model of mixed convection at a backward facing step with a rotating cylinder subjected to nanofluid

In the present study, numerical investigation of mixed convection at a backward facing step with a rotating cylinder subjected to nanofluid is conducted and a reduced order model of the system is obtained by using the proper orthogonal decomposition method. The governing equations are solved with a finite element based commercial solver. The effects of various pertinent parameters, Reynolds number, cylinder angular velocity and nanofluid volume fraction on the fluid flow and heat transfer characteristics are numerically studied. It is observed that flow field and thermal patterns change for different parameters and heat transfer enhancement is obtained for some combinations of parameters. Length averaged Nusselt number plots indicate that there is almost a linear increase in the heat transfer enhancement with increasing Reynolds number and nanoparticle volume fraction. Heat transfer enhancement is obtained for cylinder angular velocities of Ω=-4.5 and Ω=1.5. A reduced order model of the system with proper orthogonal decomposition method is obtained and it provides accurate results when compared to high fidelity CFD model of the system.

Conjugate Heat Transfer of an Internally Air-Cooled Nozzle Guide Vane and Shrouds

In order to assess the life of gas turbine critical components, it is essential to adequately specify their aerothermodynamic working environments. Steady-state analyses of the flow field and conjugate heat transfer of an internally air-cooled nozzle guide vane (NGV) and shrouds of a gas turbine engine at baseline operating conditions are numerically investigated. A high-fidelity CFD model is generated and the simulations are carried out with properly defined boundary conditions. The features of the complicated flow and temperature fields are revealed. In general, the Mach number is lower and the temperature is higher on the NGV pressure side than those on the suction side. There are two high temperature regions on the pressure side, and the temperature across the middle section is relatively low. These findings are closely related to the locations of the holes and outlets of the cooling flow passage, and consistent with the field observations of damaged NGVs. As a technology demonstration, the results provide required information for the life analysis of the NGV/shrouds assembly and improvement of the cooling flow arrangement.

High-Speed Characterization of ECN Spray A Using Various Diagnostic Techniques

Diesel spray experimentation at controlled high-temperature and high-pressure conditions is intended to provide a more fundamental understanding of diesel combustion than can be achieved in engine experiments. This level of understanding is needed to develop the high-fidelity multi-scale CFD models that will be used to optimize future engine designs. Several spray chamber facilities capable of high-temperature, igh-pressure conditions typical of engine combustion have been developed, but because of the uniqueness of each facility, there are uncertainties about their operation. The Engine Combustion Network (ECN) is a worldwide group of institutions using combustion vessels, whose aim is to advance the state of spray and combustion knowledge at engine-relevant conditions. A key activity is the use of spray chamber facilities operated at specific target conditions in order to leverage research capabilities and advanced diagnostics of all ECN participants. The first target condition, called “Spray A”, has been defined with detailed ambient and injector conditions. For this paper, we describe results from the constant-volume pre-burn vessel at Eindhoven University of Technology. The executed measurements include a wide range of diagnostics to characterize “spray A” in reacting and non-reacting conditions in great detail. Observations of spray penetration, ignition, liquid length and flame lift-off location by using several high-speed imaging diagnostics are discussed and compared with other ECN participating institutes. Comparison Spray A data from the other participating institutes, as it was presented during the 2nd ECN workshop is gathered from the ECN website database [1]. It can be concluded that the obtained results from the standardized ECN spray diagnostics, show satisfactory similarity, despite of the challenge to reach similar boundary conditions (ambient and injector) in each of the unique facilities. The differences in results are within the measurement deviation and uncertainty or can be explained by the usage of (slightly) different injectors. Combining the results of the different measurement techniques provides an overall (time resolved) overview where the different phases of fuel injection are directly linked and summarized. The presented overview provides a direct input for (CFD) modeling validation.

Uncertainty Quantification of a Flapping Airfoil with Stochastic Velocity Deviations Using the Response Surface Method

A practical flapping wing micro air vehicle should have ability to withstand stochastic deviations of flight velocities. To design a flapping airfoil with this ability, it is necessary to evaluate the impacts of velocity deviations on the flapping performances numerically or analytically. In this paper, the responses of the time-averaged thrust coefficient and the propulsive efficiency with respect to a stochastic flight velocity deviation under Gauss distribution are numerically investigated using a classic Monte Carlo method. The response surface method is employed to surrogate the high fidelity CFD model to save computational cost. It is observed that both of the time-averaged thrust coefficient and the propulsive efficiency obey a Gauss-like but not the exact Gauss distribution. The effect caused by the velocity deviation on the time- averaged thrust coefficient is larger than the one on the propulsive efficiency.

Uncertainty Quantification Integrated to CFD Modeling of Synthetic Jet Actuators

The Point Collocation Non-Intrusive Polynomial Chaos (NIPC) method has been applied to two stochastic synthetic jet actuator problems used as test cases in the CFDVAL2004 workshop to demonstrate the integration of computationally efficient uncertainty quantification to the high-fidelity CFD modeling of synthetic jet actuators. In Case1 where the synthetic jet is issued into quiescent air, the NIPC method is used to quantify the uncertainty in the long-time averaged u and v-velocities at several locations in the flow field, due to the uniformly distributed uncertainty introduced in the amplitude and frequency of the oscillation of the piezo-electric membrane. Fifth order NIPC expansions were used to obtain the uncertainty information, which showed that the variation in the v-velocity is high in the region directly above the jet slot and the variation in the u-velocity is maximum in the region immediately adjacent to the slot. Even with a ten percent variation in the amplitude and frequency, the long-time averaged u and v velocity profiles could not match the experimental measurements at y=0.1mm above the slot indicating that the discrepancy may be due to other uncertainty sources in CFD or measurement errors. In Case 2 which includes a cross flow, the free stream velocity is treated as an uncertain input variable. Fifth degree NIPC expansions were employed to quantify the uncertainty in phase averaged velocity profiles as well as long-time averaged wall pressure and skin friction coefficient distributions. The results of Case 2 show that the uncertainty in phase averaged velocity profiles gets larger when approaching the main stream. The size of a separation bubble observed in this case remains relatively insensitive to the uncertain free stream velocity within the tolerance range considered.

Improved Flutter Boundary Prediction for an Isolated Two-Degree-of-Freedom Airfoil

A novel method of computing the flutter boundary for an isolated airfoil based on a high-fidelity CFD model reveals unusual behavior at certain Mach numbers for a NACA 0012 section. Inviscid and viscous predictions of the flutter boundary for the two airfoils are compared with results from a previous experimental study. Over a narrow range of Mach numbers, unusual aeroelastic response behavior occurs, and inviscid and viscous predictions dier significantly. Also in this range, solutions show increased sensitivity to grid topology as well as flow Mach number. This is found to be a consequence of flow shedding which occurs over a narrow range of Mach numbers. The nature of this shedding is captured only by using a greatly refined viscous grid, and unusual numerical results occur when using coarser viscous and inviscid meshes.

A High-Fidelity CFD Model of Methane Steam Reforming in a Packed Bed Reactor

A novel high-fidelity CFD model is proposed for the process optimization and intensification of methane steam reforming in a packed bed reactor. The random packing of spherical particles is constituted by simulating a dumping of particles into the annular reactor by a commercial code based on discrete element method (DEM). The complex spatial geometry between hundreds of particles is created associated with a developed interparticle bridge method, which eliminates the interparticle and particle–wall contact regions by assuming that the small regions are stagnant and would not affect the reactor behavior. The conservation equations of mass, momentum, energy and chemical species are fully solved by employing a commercial CFD code based on finite volume method. A newly coded subroutine is incorporated into the CFD code to evaluate the reaction rates according to the species partial pressures and temperature on each surface cell covering the particles. The values of reaction, equilibrium and adsorption constants are specified based on the experiments in the literature. According to the reaction rates, the mass and heat sources are given to each fluid cell on the surface cell. It is verified that the developed CFD model is capable of predicting the distributions of species and temperature microscopically as well as macroscopically for methane steam reforming. The present DEM–CFD procedure enables one to investigate the behavior of packed bed reactor in detail once the catalyst is characterized in a conventional way. Therefore it would become a powerful tool to optimize and intensify any process in a packed bed reactor where the plug flow assumption is invalid.

Evolutionary methods for multidisciplinary optimization applied to the design of UAV systems†

The implementation and use of a framework in which engineering optimization problems can be analysed are described. In the first part, the foundations of the framework and the hierarchical asynchronous parallel multi-objective evolutionary algorithms (HAPMOEAs) are presented. These are based upon evolution strategies and incorporate the concepts of multi-objective optimization, hierarchical topology, asynchronous evaluation of candidate solutions, and parallel computing. The methodology is presented first and the potential of HAPMOEAs for solving multi-criteria optimization problems is demonstrated on test case problems of increasing difficulty. In the second part of the article several recent applications of multi-objective and multidisciplinary optimization (MO) are described. These illustrate the capabilities of the framework and methodology for the design of UAV and UCAV systems. The application presented deals with a two-objective (drag and weight) UAV wing plan-form optimization. The basic concepts are refined and more sophisticated software and design tools with low- and high-fidelity CFD and FEA models are introduced. Various features described in the text are used to meet the challenge in optimization presented by these test cases.