Dragos Isvoranu

Numerical Simulation of Combustion and Rotor-Stator Interaction in a Turbine Combustor

This article presents the development of a numerical algorithm for the computation of flow and combustion in a turbine combustor. The flow and combustion are modeled by the Reynolds-averaged Navier-Stokes equations coupled with the species-conservation equations. The chemistry model used herein is a two-step, global, finite-rate combustion model for methane and combustion gases. The governing equations are written in the strong conservation form and solved using a fully implicit, finite-difference approximation. The gas dynamics and chemistry equations are fully decoupled. A correction technique has been developed to enforce the conservation of mass fractions. The numerical algorithm developed herein has been used to investigate the flow and combustion in a one-stage turbine combustor.

Radiation exergy: the case of thermal and nuclear energy

This study presents several methods to evaluate the exergy of thermal and nuclear radiation. First, a general treatment is developed for the thermal radiation exergy flux. Second, the exergy of thermal radiation is derived from a simple, general, original thermodynamic argument. Third, the state of the art concerning the accurate upper bounds for the conversion efficiency of thermal radiation into work is briefly presented. Fourth, the exergy of nuclear radiation is derived.

Mixed Domain Macromodels for RF MEMS Capacitive Switches

A method to extract macromodels for RF MEMS switches is proposed. The macromodels include both the coupled structural-electric behavior of the switch as well as its RF behavior. The device with distributed parameters is subject to several analyses from which the parameters of the macromodel are extracted, by model reduction. From the coupled structural-electrostatic analysis the parametric capacitance and the effective stiffness coefficients of the switch are extracted. From the RF characteristics in the up stable state, the transmission line parameters are extracted. Finally, all parameters are combined in a Spice circuit model, which is controlled by the MEMS actuation voltage and is excited with the RF signal. The procedure is applied to a capacitive switch. Relative modeling errors with respect to the non-reduced model, considered as reference, of less than 3 % for the RF characteristics and less than 1 % for the mechanical characteristics are obtained.

Hydrodynamics of tsunamis generated by asteroid impact in the Black Sea

Two-dimensional and one-dimensional models are used to evaluate the seashore effects of the tsunami generated by an asteroid hitting the deep water in the Eastern region of the Black Sea. The shallow water theory has been used to describe tsunami propagation. The distance between the impact point and the nearest coast is about 150 km. The effects on the coastal regions depend on many factors among which the most important is asteroid size. The tsunami generated by a 250 m asteroid reaches the nearest dry land location in 20 minutes and needs about two hours to hit all over the Black Sea coast. The horizontal inundation length is also known as run-in or run-off distance, according to the direction of water movement. The run-up values may be up to 39 m in the Eastern basin and a more than ten times smaller in theWestern region. The Northern part of the Black Sea coast is not affected by the tsunami. The run-in values of a tsunami generated by a 1000 m diameter asteroid are sensibly larger than the similar values associated to a 250 m diameter asteroid. The run-in strongly depends on the distance from the impact position to the shore and on coastal topographical profile. For instance, the run-in distance in case of a tsunami generated by a 250 m size asteroid is 0.1 km (at Varna), 0.5 km (Ordu), 0.7 km (Yalta) and 1.4 km (Sochi). In case of the 1000 m diameter asteroid the run-in distance is 0.7 km (at Varna) and 2.9 km (Yalta). The results accuracy is also discussed.

Proper Orthogonal Decomposition Applied to a Turbine Stage with In-Situ Combustion

The paper presents a POD analysis of the numerical simulation results obtained from the numerical simulation of transport phenomena in a one-stage turbine-combustor (i.e. a turbine stage with in situ combustion). The motivation of this research is to investigate the new fuel injection concept that consists of a perforated pipe placed at mid-pitch in the stator row passage and different axial positions. The main goal of this simulation is to assess the stability of the in situ combustion with respect to the unsteadiness induced by the rotor-stator interaction. To identify the sources of instability for this complex flow, the proper orthogonal decomposition technique is used to analyze the natural patterns and couplings between various modes of pressure, temperature, velocity and chemical production rate distributions.

Extraction of lumped structural parameters from multiphysics field simulations for MEMS switches

This paper investigates the extraction of lumped parameters (elastic coefficient and effective mass) for RF MEMS switches. The extraction starts from field simulations obtained with the finite element method, which solves strongly coupled structural-electrostatic field problems, and is based on least square fitting. The elastic coefficients are extracted from static coupled simulations, whereas the effective mass is extracted from a dynamic, without damping, unforced, transient simulation. The degree of system nonlinearity can be estimated from the static simulation. If the system is close to linearity with respect to its structural behavior, then a simple algorithm to extract the effective mass is proposed. The validations are carried out by comparing the initial field results with the results obtained from the reduced order models. Relative errors less than 8 % are obtained for the pull-in voltage for all the structures investigated.

Combined POD and Field Analysis of a Turbine Stage with In Situ Reheat

This paper presents a follow-up of the numerical simulation of flow and combustion in a one stage turbine combustor (turbine stage in situ combustion). The main purpose of the simulation is to respond to the questions raised by our previous studies concerning the applicability of the two equations Westbrook-Dryer chemical mechanism (WD2) in their original form. Based on proper orthogonal decomposition analysis, it was found that the reaction rates cannot be reconstructed using only a few modes as all other state variables do. The same injection concept and CAD model as in previous studies is used. We found out that reducing grid size can have a great impact on how well the reaction mechanism correlates with other flow variables.

POD ANALYSIS OF THE REACTION RATES IN A TURBINE STAGE WITH IN SITU COMBUSTION

This paper presents the in-situ combustion concept and preliminary numerical results in a one stage turbine combustor. The main purpose of the simulation is to assess the stability of the in situ combustion with respect to the unsteadiness induced by the rotor-stator interaction. In order to identify information on the sources of instability for this complex flow, proper orthogonal decomposition technique is adopted to analyze the natural patterns and couplings between various modes of pressure, temperature, velocity and chemical production rate distributions. The major find of this investigation is that contrary to all other primitive variables, the reconstruction of chemical reaction rates needs a larger number of energy modes to attain a reasonable normalized error.

Kinematics and flow characteristics of a magnetic actuated multi-cilia configuration

The current paper continues the analysis of a completely novel method of fluid manipulation technology in micro-fluidics systems, inspired by nature, namely by the mechanisms found in ciliates. More information on this subject can be found at http://www.hitech-projects.com/euprojects/artic/. In order to simulate the drag forces acting on an array of artificial cilia, we have developed a computer code that is based on fundamental solutions of Stokes flow in a semi-infinite domain. The actuation mechanism consists of a bi-directional rotating excitation magnetic field. The magnetization induced by the magnetic field was calculated in a separate routine based on the Integral Nonlinear Equations Approach with 1D discretization of wire (cilium). Time averaged x-coordinate mass flow rates, streamlines and vorticity field are computed for several cilium configurations. The outcome and originality of this paper consist on assessing magnetic actuation as a practical tool for obtaining a consistent one-directional fluid flow.

NOx re-burn simulation in a double-jet counter-flow flame

The paper investigates the main features of NOx emission in a laminar double-jet counter-flow diffusion flame for later use as a possible physical model for NOx reduction through turbine in situ reheat. The oxidizer stream consists of exhaust gas resulted from a conventional combustor and the fuel stream is represented by an air?methane mixture. The main interest rests on the distribution of NOx species and especially on NO production rate that controls the pollutant emission index. The most interesting outcome of the research is that NO emission index has a minimum value depending on the equivalence ratio of the air?methane mixture.