Constantin Rotaru

An Extended Combustion Model for the Aircraft Turbojet Engine

Abstract The paper consists in modelling and simulation of the combustion in a turbojet engine in order to find optimal characteristics of the burning process and the optimal shape of combustion chambers. The main focus of this paper is to find a new configuration of the aircraft engine combustion chambers, namely an engine with two main combustion chambers, one on the same position like in classical configuration, between compressor and turbine and the other, placed behind the turbine but not performing the role of the afterburning. This constructive solution could allow a lower engine rotational speed, a lower temperature in front of the first stage of the turbine and the possibility to increase the turbine pressure ratio by extracting the flow stream after turbine in the inner nozzle. Also, a higher thermodynamic cycle efficiency and thrust in comparison to traditional constant-pressure combustion gas turbine engines could be obtained.

ASPECTS REGARDING VELOCITY DISTRIBUTION IN THE SECONDARY ZONE OF A GAS TURBINE COMBUSTOR

This paper deals with the modelling and simulation of the combustion in a turbojet engine in order to find the velocity distribution in the secondary zone of the flame tube. The Arrhenius relationship, which describes the basic dependencies of the reaction rate on pressure, temperature and concentration, has been used. Also, combustion efficiency has been defined and related to both the exhaust temperature and species concentration. Premixed laminar flames and the dependence of propagation rate on temperature and the fuel-air ratio have been highlighted. The main focus of this paper consists in a new configuration of the aircraft engine combustion chamber with an optimal distribution of gas velocity in front of the turbine. This constructive solution could allow a lower engine rotational speed, a lower temperature in front of the first stage of the turbine and the possibility to increase the turbine pressure ratio. Also, a higher thermodynamic cycle efficiency and thrust in comparison to traditional constant-pressure combustion gas turbine engines could be obtained.

Aircraft engine mathematical model – linear system approach

This paper examines a simplified mathematical model of the aircraft engine, based on the theory of linear and nonlinear systems. The dynamics of the engine was represented by a linear, time variant model, near a nominal operating point within a finite time interval. The linearized equations were expressed in a matrix form, suitable for the incorporation in the MAPLE program solver. The behavior of the engine was included in terms of variation of the rotational speed following a deflection of the throttle. The engine inlet parameters can cover a wide range of altitude and Mach numbers.

MATHEMATICAL MODEL AND CFD ANALYSIS OF PARTIALLY PREMIXED COMBUSTION IN A TURBOJET

In this paper are presented some results about the study of combustion chamber geometric configurations that are found in aircraft gas turbine engines. The CFD simulations were made with jet A fuel (which is presented in the Fluent software database) for an annular flame tube with 24 injectors. The temperature profile at the turbine inlet exhibits nonuniformity due to the number of fuel injectors used in the circumferential direction, the spatial nonuniformity in dilution air cooling and mixing characteristics as well as other secondary flow patterns and instabilities that are set up in the flame tube. The results show that a spiral (helicoidal) holes distribution could improve the flame tube efficiency, turbulent vortex influence and the actual rate of heat release.

Inertial sensor signals denoising with directed transfer function

In order to achieve precise navigation information on the displacement of a vehicle in terms of position, speed, acceleration and direction we are suggesting the use of a new software procedure for processing data received from miniaturized inertial navigation systems. A new method for establishing the optimum decomposition level of the Wavelet transform is proposed. This method was used for filtering variable acceleration signals received from an accelerometer. In our next investigations we intend to implement this algorithm for the pre-calibration of two or tri-dimensional navigation systems containing miniaturized accelerometers and gyros.

FEM analysis of one element prosthesis on dental implant

In this paper, a complete biomechanical system made up of bone, implant and ceramic crown under axial loading is investigated by Finite Element Method (FEM). The system response evaluation has a major role in detecting the critical zones where possible damage, failure or rupture may occur jeopardizing the implant stability. Very accurate 3D geometrical model is used to calculate the stress, strain and displacement state in implant and surrounding bone. This analysis is completely concordant with clinical studies.

A COMPARATIVE ANALYSIS BETWEEN TWO TYPES OF VEHICLES WHICH COULD BE USED AS UAV LAUNCHERS MOBILE PLATFORM

The following scientific study is about of two possibilities to use different types of vehicles as mobile platform which could be used to launch an UAV. One of them is a light off-road articulated prototype vehicle, DAC 2.65 FAEG and the other one is a classic off-road vehicle named BCV-320, prototype too. Both of them are going to be integrated into a mobile cell for forward reconnaissance missions. The advanced multi-criteria analysis method is going to be used by the researchers in order to establish the best solution for a mobile platform capable to launch different types of UAV’s. Due to the fact that both suggested prototype vehicles have high modularity, the final conclusions are very interesting and some test exercise in military fields is going to be done.

Staggered Approach for Fluid-Structure Interaction Phenomena of an AGARD 445.6 Wing Using Commercial CFD/CSM Software

This paper presents the development of an efficient time-marching simulation technology for fluid-structure interaction applications using commercial computational fluid dynamics (CFD) and computational solid mechanics (CSM) software and in-house modules. By splitting the multidisciplinary coupling problem into three major analysis fields (the fluid field, the structure field, and the moving mesh pseudofield) one can solve each field using already available and validated software and the coupling between the different analysis fields can be accomplished by in-house software (FORTRAN and C codes). This simulation technology is able to predict both unsteady interaction phenomena and nonlinear aeroelastic problems in reasonable time, taking advantage of a high-performance computing network. Commercial CFD software was used to solve the Navier-Stokes equations and the chosen turbulence models of the fluid field while the structural field was solved using commercial CSM software. The transfer of information from the fluid field to the structural field and vice versa is computed by an in-house interpolation module, which reduces the user interaction to a minimum initialization. The third field, the moving mesh, was solved with another in-house code, which employs the spring network analogy and the elastic material analogy. The advancement of the solution is controlled by means of FORTRAN and C codes that manage the run/wait conditions of software modules based on the staggered procedures proposed in previous research. The proposed aeroelastic simulation technology was validated with the experimental data available for the advisory group for aerospace research and development (AGARD) 445.6 standard aeroelastic configuration for dynamic response at subsonic and transonic free stream Mach numbers.

NUMERICAL INVESTIGATION OF MIXED FLOWS TURBOFAN ENGINE THRUST CORRELATED WITH THE COMBUSTION CHAMBER'S PARAMETERS

The purpose of this paper is to show the influence of the most relevant parameters of the combustion chamber (e.g. perturbations in the turbine inlet temperature T3T and pressure losses) and the predicted performances of a mixed flows turbofan engine. The performances of the mixed flow turbofan engine have been predicted by following the numerical simulation of the engines operation, with an in-house developed code, based on a comprehensive mathematical model of the mixed flow turbofan engine. The investigation is carried on at the engines design point, which means 100% rotational speed, at sea level static standard atmosphere conditions. The most significant parameters of the combustion chamber, namely the combustion chambers pressure losses and the perturbations in the turbine inlet temperature T3T have been chosen such that to match the standpoint of the fighter pilot; the most relevant parameter is the turbine inlet temperature T3T. The numerical results are summarized as graphs and charts, from which one can express new correlations and further, a new command and control law for the turbojet engines operation can be concluded. The contributions of this study may prove to have practical applications, for being used both for training the pilot students and during flight operation, for contributing to a significant improvement in flight safety, which can be of real help for fighter pilots.

NUMERICAL INVESTIGATION OF TURBOJET ENGINE THRUST CORRELATED WITH THE COMBUSTION CHAMBER'S PARAMETERS

The purpose of this paper is to highlight the correlation between the thrust as the main performance of a turbojet engine and the parameters of the combustion chamber, e. g. the pressure losses and the influence of the perturbations in the turbine inlet temperature T3T. The performances of the turbojet engine have been predicted by following the numerical simulation of the engines operation, with an in-house developed code, based on a comprehensive mathematical model of the turbojet engine. The investigation is carried on at the engines design point, which means 100% rotational speed, at sea level static standard atmosphere conditions. The most significant parameters of the combustion chamber, namely the combustion chambers pressure losses and the perturbations in the turbine inlet temperature T3T have been chosen such that to match the standpoint of the fighter pilot; the most relevant parameters is the turbine inlet temperature T3T. The numerical results are summarized as graphs and charts, from which one can express new correlations and further, a new command and control law for the turbojet engines operation can be concluded. The contributions of this study may prove to have practical applications, for being used both for training the pilot students and during flight operation, for contributing to a significant improvement in flight safety, which can be of real help for fighter pilots.