Air-breathing Propulsion Engine Research Articles

Numerical Analysis of Modified Spike in Ramjet Engine

The main objective of this paper is to study the efficiency of ramjet engine by optimizing the inlet spike geometry. The engine inlet is of primary importance for all air-breathing propulsion engines. Its major function is to collect the atmospheric air at free stream Mach number, slow it down and to compress it efficiently. The geometries used here are planar with different Mach numbers 1.5, 2, 3 and 3.5. The first inlet has a cone of with four types of different half cones angles of 14°, 15°, 16° and 17° respectively. In the second modified inlet, a hole of 0.3 mm is made at mid-section of the cone on 2 symmetrical sides of the cone. It is observed that the hole allows the inflow of oblique shock i.e., the oblique shock is absorbed through the holes, followed by normal shock which then expands behind the length of the cone thus increasing the mass flow rate for adequate combustion. In the last modified inlet, the cone is step ended due to which the mass flow converges as it flows along the slope of the steps. The designing is done in solid works and the analysis of inlet spike is done in 2-D with the help of ANSYS software. It is finally concluded that the out of the four different cone angles analysed, 170 cone angle for M = 1.5 showed least pressure recovery and the same geometry is analysed for two different modified spikes where the cone with hole (cavity) showed huge rise pressure for the same conditions.

Analysis of supersonic shear effects on flame characteristics of an evaporating flame-holder

Flame stabilization and its interaction with flow characteristics are crucial to the development of air-breathing propulsion engine. In this paper, experiments and numerical simulations have been conducted in both uniform and nonuniform inflowing streams to investigate supersonic shear effects on flame characteristics of an evaporating-flame holder. Specifically, supersonic shear is imposed by introducing a mixing layer between a subsonic stream of Mach number Ma=0.15 and a supersonic stream of Ma=1.55. The flames are imaged by high-speed photography with the flame boundary being identified. Three dimensional simulations with k-ε turbulence model, discrete phase model (DPM) for liquid droplets, and eddy-dissipation-concept (EDC) combustion model, are further performed to shed lights on the complex flow characteristics and interactions with flame shapes. Results show that the vortex structure and the size of recirculation zone after the flame holder are similar with and without shear implying that the presence of shear flow will not affect flame stabilization. The supersonic shear instead can modulate the flame shape and location within a combustor by shortening 30% of the overall flame length. Specifically, the hot products can be pulled away from the top wall and entrained towards the mixing layer. The flame shape is less sensitive to the increase of fuel supply due to the blockage of flame development from the recirculation zone in further downstream and the flame being entrained toward the mixing layer. Further flow and fuel/air mixing analysis shows that the outer shear layer of the recirculation zone after the flame holder plays an important role on flame stabilization. The flame front adjusts adaptively with the spatial distribution of the outer shear layer, which would be modulated by the presence of supersonic shear.

Optimization study on the isolator length of dual-mode scramjet

The dual-mode scramjet is a prime candidate for air-breathing propulsion engines given its broad speed range and high efficiency. The detailed structure of the pseudo-shock wave in the isolator is worth investigating. Therefore, the present study investigates the effect of isolator length on the pseudo-shock wave. We replicate the experimental work of the reference paper with a two-dimensional numerical model. Pressure distribution on the body surface is applied in the numerical validation. The numerical result is in good agreement with that of the existing experimental work. We simulate the thermal choking condition with a throttling device. As the throat area of throttling device decreases, the back pressure continues increasing and the pseudo-shock wave moves upstream. Avoiding unstart phenomenon is a key objective in the operation of dual-mode scramjet. Therefore, we investigate the critical condition shortly before unstart phenomenon occurs. The pseudo-shock wave structure is described by pressure distribution. Our main objective is to explore the effect of isolator length on the dual-mode scramjet. The optimal isolator length depends on the maximum back pressure and total pressure loss in the critical condition shortly before the unstart phenomenon occurs. The maximum back pressure in the critical condition is higher when the isolator length ranges from 8.7 to 20.7. The total pressure loss in the critical condition decreases at the beginning and then increases when the isolator length ranges from 8.7 to 20.7.

Numerical simulation of air/H<SUB align=right>2 combustion processes in a scramjet turbulent flow

The aim of this work is to develop a numerical approach, based on the Favre's averaged Navier-Stokes equations coupled with a turbulence model and with a complex finite rate Air/Hydrogen combustion kinetic model to simulate the unsteady axisymetric supersonic hydrogen-air mixing processes. The main application is dedicated to the scramjet hypersonic air-breathing propulsion engine. To achieve this goal the Spalart-Allmaras turbulence model (SA) with correction terms to model the compressibility effects and the complete finite rate chemistry model of Jachimowsky involving 13 species and 153 reactions have been implemented in a finite volume code.

Lessons Learned During Solutions of Multidisciplinary Design Optimization Problems

Optimization research at NASA Glenn Research Center has addressed the design of structures, aircraft and airbreathing propulsion engines. During solution of the multidisciplinary problems several issues were encountered. This paper lists four issues and discusses the strategies adapted for their resolution: (1) The optimization process can lead to an inefficient local solution. This deficiency was encountered during design of an engine component. The limitation was overcome through an augmentation of animation into optimization. (2) Optimum solutions obtained were infeasible for aircraft and air-breathing propulsion engine problems. Alleviation of this deficiency required a cascading of multiple algorithms. (3) Profile optimization of a beam produced an irregular shape. Engineering intuition restored the regular shape for the beam. (4) The solution obtained for a cylindrical shell by a subproblem strategy converged to a design that can be difficult to manufacture. Resolution of this issue remains a challenge. The issues and resolutions are illustrated through six problems: (1) design of an engine component, (2) synthesis of a subsonic aircraft, (3) operation optimization of a supersonic engine, (4) design of a wave-rotor-topping device, (5) profile optimization of a cantilever beam, and (6) design of a cvlindrical shell. The combined effort of designers and researchers can bring the optimization method from academia to industry.

General-purpose optimization method for multidisciplinary design applications

A general-purpose optimization tool for multidisciplinary applications, which in the literature is known as COMETBOARDS, is being developed at NASA Lewis Research Center. The modular organization of COMETBOARDS includes several analyzers and state-of-the-art optimization algorithms along with their cascading strategy. The code structure allows quick integration of new analyzers and optimizers. The COMETBOARDS code reads input information from a number of data files, formulates a design as a set of multidisciplinary nonlinear programming problems, and then solves the resulting problems. COMETBOARDS can be used to solve a large problem, which can be defined through multiple disciplines, each of which can be further broken down into several subproblems. Alternatively, a small portion of a large problem can be optimized in an effort to improve an existing system. Some of the other unique features of COMETBOARDS include design variable formulation, constraint formulation, subproblem coupling strategy, global scaling technique, analysis approximation, use of either sequential or parallel computational modes, and so forth. The special features and unique strengths of COMETBOARDS assist convergence and reduce the amount of CPU time used to solve the difficult optimization problems of aerospace industries. COMETBOARDS has been successfully used to solve a number of problems, including structural design of space station components, design of nozzle components of an air-breathing engine, configuration design of subsonic and supersonic aircraft, mixed flow turbofan engines, wave rotor topped engines, and so forth. This paper introduces the COMETBOARDS design tool and its versatility, which is illustrated by citing examples from structures, aircraft design, and air-breathing propulsion engine design.

Optimization of air-breathing propulsion engine concept

The design optimization of air-breathing propulsion engine concepts has been accomplished by soft-coupling the NASA Engine Performance Program (NEPP) analyser with the NASA Lewis multidisciplinary optimization tool COMETBOARDS. Engine problems, with their associated design variables and constraints, were cast as non-linear optimization problems with thrust as the merit function. Because of the large number of mission points in the flight envelope, the diversity of constraint types, and the overall distortion of the design space, the most reliable optimization algorithm available in COMETBOARDS, when used by itself, could not produce satisfactory, feasible, optimum solutions. However, COMETBOARDS' unique features–which include a cascade strategy, variable and constraint formulations, and scaling devised especially for difficult multidisciplinary applications–successfully optimized the performance of subsonic and supersonic engine concepts. Even when started from different design points, the combined COMETBOARDS and NEPP results converged to the same global optimum solution. This reliable and robust design tool eliminates manual intervention in the design of air-breathing propulsion engines and eases the cycle analysis procedures. It is also much easier to use than other codes, which is an added benefit. This paper describes COMETBOARDS and its cascade strategy and illustrates the capabilities of the combined design tool through the optimization of a high-bypass-turbofan wave-rotor-topped subsonic engine and a mixed-flow-turbofan supersonic engine. ©1997 John Wiley & Sons, Ltd.

Cascade Optimization Strategy for Aircraft and Air-Breathing Propulsion System Concepts

Design optimization for subsonic and supersonic aircraft and for air-breathing propulsion engine concepts has been accomplished by soft-coupling the Flight Optimization System (FLOPS) and the NASA Engine Performance Program analyzer (NEPP), to the NASA Lewis multidisciplinary optimization tool COMETBOARDS. Aircraft and engine design problems, with their associated constraints and design variables, were cast as nonlinear optimization problems with aircraft weight and engine thrust as the respective merit functions. Because of the diversity of constraint types and the overall distortion of the design space, the most reliable single optimization algorithm available in COMETBOARDS could not produce a satisfactory feasible optimum solution. Some of COMETBOARDS' unique features, which include a cascade strategy, variable and constraint formulations, and scaling devised especially for difficult multidisciplinary applications, successfully optimized the performance of both aircraft and engines. The cascade method has two principal steps: In the first, the solution initiates from a user-specified design and optimizer, in the second, the optimum design obtained in the first step with some random perturbation is used to begin the next specified optimizer. The second step is repeated for a specified sequence of optimizers or until a successful solution of the problem is achieved. A successful solution should satisfy the specified convergence criteria and have several active constraints but no violated constraints. The cascade strategy available in the combined COMETBOARDS, FLOPS, and NEPP design tool converges to the same global optimum solution even when it starts from different design points. This reliable and robust design tool eliminates manual intervention in the design of aircraft and of air-breathing propulsion engines where it eases the cycle analysis procedures. The combined code is also much easier to use, which is an added benefit. This paper describes COMETBOARDS and its cascade strategy and illustrates the capability of the combined design tool through the optimization of a subsonic aircraft and a high-bypass-turbofan wave-rotor-topped engine.

Combustion Measurements in Air Breathing Propulsion Engines. Survey and Research Needs

Abstract —The current measurement needs of the jet engine combustion engineers and scientists are considered. An assessment is made of the potential of probe and optical technologies to meet them. In the first part, the available instrumentation are evaluated and compared for the following criteria: non-interfering access to the flow, specificity, accuracy, sensitivity, space and time resolution, and cost effectiveness. The flow properties of interest are: velocity, pressure, temperature and the components of the flow (N2, O2, CO2, H2O, CO, NO, NO2, OH, THC's and smoke). In the second part, the different needs of the development engineer, the combustor researcher and the fundamental combustion scientist are established separately. Desirable levels of measurement criteria are proposed for all three situations. Several experiments are suggested.