Volume 39, Issue 4

Advanced mathematical model has been developed for design and analysis of turbojet engines. It includes closed form algebraic equation for critical pressure and optimum pressure ratio at maximum thrust. The model and the algebraic equations consider efficiencies, pressure recovery rates meanwhile the gas parameters are the function of the fuel to air ratio and the temperature. РД-9Б and АЛ-21Ф3 engines are applied for demonstrating the capabilities of the calculation process. The unknown parameters as efficiencies, pressure recovery rates, power reduction rate of the auxiliary systems, bleed air ratio, air income ratio due to blade cooling and total temperature in the afterburner were identified by constrained optimization. The effect of i. T 04 /T 02 ratio for the thrust and TSFC in the function of compressor pressure ratio, ii. the real (viscous) flow conditions and iii. the temperature and fuel to air ratio on gas parameters were also investigated for verification and plausibility check.

A promising method of reducing NOx emissions in combustion systems is the Flameless oxidation (FO), which is based on significant dilution of the oxygen concentration in the reactant stream and elevating its temperature to above auto ignition level. The present work is aimed at developing an FO based combustor for a sequential combustion turbofan engine, where the primary combustor is fuelled with H 2 and the secondary combustor with hydrocarbon (jet or bio-jet) fuel. The work was performed within the framework of the European project AHEAD (www.ahead-euproject.eu). Being situated between the high pressure and the low pressure turbines, the inlet conditions to the FO combustor are non-conventional. CHEMKIN simulations revealed the theoretical feasibility of a combustion system to operate in the FO mode of combustion under the specific Take-off and Cruise operating conditions. Several design iterations were conducted to find an appropriate geometrical configuration that would allow for such a system to operate in a stable manner. The design iterations were followed by CFD simulations (FLUENT) and a final design was an achieved where the predictions indicated nearly uniform internal temperature distribution with low mass fraction of CO and NOx at the exhaust.

A comprehensive exergetic, exergoeconomic and exergoenvironmental analyses of a turbojet engine are performed to determine how the hydrogen fuel usage affects the exergetic and exergoeconomic performances of the turbojet engine. The exergy efficiency of the engine reduces from 15.40 % to 14.33 % while the waste exergy rate increases from 22.31 GJ/h to 24.01 GJ/h. However, the high increase in the fuel cost rate and specific fuel exergy cost with the hydrogen fuel causes that the specific product exergy cost rises up from 134.69 US$/GJ to 355.11 US$/GJ. The environmental impact of CO 2 decreases by 99.12 % while the environmental damage cost rate lessens by 112.16 % with hydrogen usage. In this regard, the environmental damage cost rate decreases from 322.50 US$/h to 2.85 US$/h. The exergoenvironmental cost rate is determined to be 869.64 US$/h for jet fuel while it is obtained to be 1429.32 US$/h for hydrogen fuel. In this case, the specific exergoenvironmental cost is calculated to be 214.08 US$/GJ for jet fuel and 355.82 US$/GJ for hydrogen fuel.

In this paper, a model reference adaptive sliding mode control method is proposed for a variable cycle engine (VCE) which is a MIMO system with uncertainties and external disturbances. The reference model is designed based on optimal LQR method to provide ideal reference states. An adaptive sliding mode controller (ASMC) is designed for model reference adaptive control structure, which the adaptive law is derived based on Lyapunov function to estimate the unknown upper bound of uncertainties and external disturbances. Simulation results for VCE demonstrate the performance and fidelity of the proposed method.

The present study deals with the numerical study of the mixing process in a 2D supersonic ejector. The performance parameters such as momentum flux, degree of mixing and stagnation pressure loss are used to analyse mixing process. The evolution of the kinetic energy of turbulence is also observed. The investigation is carried out on a conventional 2D supersonic ejector and on a 2D supersonic ejector equipped with wall slot injectors along the mixing chamber. The performance parameters show a significant mixing enhancement when transverse micro-jets are used.

This paper focuses on the internal flow development of an S-shaped diffusing duct. Based on the experimental result of total pressure recovery coefficient, the Reynolds stress model (RSM) was selected as a suitable turbulence model for the present study. The numerical results show that 6.2 times the area ratio of the exit to inlet and the aggressive deflection at the first bend of the lower wall lead to strong adverse pressure gradient and very large flow separation, and create a pair of counter-rotating vortices along streamwise direction. The duct diffuser efficiency is 72.37 %. The area-averaged total pressure recovery coefficient at the exit of the duct is 0.9814, and the synthesis distortion index DC (60) is 0.7081.

Effect of nozzle geometries on the propagation of twin jet issuing from nozzles with circle-circle, circle-ellipse, circle-triangle, circle-square, circle-hexagon and circle-star geometrical combinations was investigated for Mach numbers 0.2, 0.4, 0.6 and 0.8. In all the cases, both jets in the twin jet had the same Mach number. All the twin jets of this study are free jets, discharged into stagnant ambient atmosphere. The result of the twin jets issuing from circle-circle nozzle is kept as the reference in this study. For all the twin jet nozzles, the inter nozzle spacing; the distance between the nozzle axes (S) was 20 mm and all the nozzles had an equivalent area of 78.5 mm 2 . Thus for all the cases of the present study, S/D ratio is 2. The results show that the mixing of the combined jet, after the merging point is strongly influenced by the combined effect of the nozzle geometry and jet Mach number. Among the six different twin jet nozzle configuration studied, circle-square combination is found to be the most superior mixing promoter.

The main purpose of this paper is to analyze the characteristics of the flow field in fan rotor. Nowadays the twisted and swept fan is the representative work of the forefront of aerospace engines. The tip clearance flow field can have a large impact on fan rotor performance. This article describes and uses the throttle method to obtain near stall condition. Near stall condition value simulation of the transonic fan rotor was carried out by CFX. The Proper Orthogonal Decomposition method was applied to the tip flow-field analysis. The main structure of the flow field can be distinguished by Proper Orthogonal Decomposition method. Then the flow structure is sorted according to energy. Disturbing fine flow structures can also be captured. This provides a comparative reference for flow field visualization. It also provides important data for the design of the fan.

For improving the response performance of engine, a novel aero-engine control method based on Deep Q Learning (DQL) is proposed. The engine controller based on DQL has been designed. The model free algorithm – Q learning, which can be performed online, is adopted to calculate the action value function. To improve the learning capacity of DQL, the deep learning algorithm – On Line Sliding Window Deep Neural Network (OL-SW-DNN), is adopted to estimate the action value function. For reducing the sensitivity to the noise of training data, OL-SW-DNN selects nearest point data of certain length as training data. Finally, the engine acceleration simulations of DQR and the Proportion Integration Differentiation (PID) which is the most commonly used as engine controller algorithm in industry are both conducted to verify the validity of the proposed method. The results show that the acceleration time of the proposed method decreased by 1.475 second while satisfied all of engine limits compared with the tradition controller.

An improved mean streamline loss model for splittered centrifugal/mixed-flow compressor impellers is presented. One-dimensional model predictions, CFD simulations and experimental results for Krain impeller are compared to confirm the model validity. A new description for the interaction between blade number and splitter blade length of a splittered mixed-flow compressor impeller with high hub/tip ratio is discussed and formulized. The optimal principal blade number and optimal splitter blade length corresponding to maximum impeller efficiency are selected by the new formulas studied. The results indicate that the improved model and new formulas have reasonable prediction effects for the impeller efficiency and the selection of blade number and splitter blade length. Blade height/pitch ratio can also be adopted as a selection reference especially for high hub/tip impellers. Effective blade number or equivalent solidity is only suitable for evaluating load capacity rather than efficiency in impeller design processes.

The present numerical study is to understand the effect of air tabs located at the exit of a convergent nozzle on the spreading and mixing characteristics of correctly expanded sonic primary jet. Air tabs used in this study are two secondary jets issuing from constant diameter tubes located diametrically opposite at the periphery of the primary nozzle exit, normal to the primary jet. Two air tabs of Mach numbers 1.0 to 1.4, in steps of 0.1 are considered in this study. The mixing modification caused by air tabs are analysed by considering the mixing of uncontrolled (free) primary jet as a reference. Substantial enhancement in jet mixing is achieved with Mach 1.4 air tabs, which results in 80 % potential core length reduction. The total pressure profiles taken on the plane (YZ) normal to the primary jet axis, at various locations along the primary jet centreline revealed the modification of the jet cross sectional shape by air tabs. The stream-wise vortices and bifurcation of the primary jet caused by air tabs are found to be the mechanism behind the enhanced jet mixing.

In the highly-loaded turbine blade passage, cross flow is driven by the lateral gradient. It strongly influences the cooling performances in the endwall region. In this research, the effect of cross flow on the shaped film cooling hole is studied by Large Eddy Simulation (LES); modal analysis is conducted with an incremental POD (iPOD) approach, which makes the analysis of the large data sets from LES feasible. It is shown that the symmetry of the counter rotating vortex pair (CRVP) is destroyed. The large-scale vortex induced by end-wall cross flow plays an important role in both shape and convection of hairpin vortices and horseshoe vortices, which influences the coolant distribution. This study suggests that the effects of cross flow should be considered for the design of end-wall film cooling. It also indicates the high efficiency of the iPOD approach, which can be used to analyze large amounts of high-dimensional data.

Natural frequencies and vibration modes of axial compressor blades are investigated. A refined mathematical model based on the usage of an eight-nodal curvilinear isoparametric finite element was applied. The verification of the model is carried out by finding the frequencies and vibration modes of a smooth cylindrical shell and comparing them with experimental data. A high-precision experimental setup based on an advanced method of time-dependent electronic interferometry was developed for this aim. Thus, the objective of the study is to verify the adequacy of the refined mathematical model by means of the advanced time-dependent electronic interferometry experimental method. The divergence of the results of frequency measurements between numerical calculations and experimental data does not exceed 5 % that indicates the adequacy and high reliability of the developed mathematical model. The developed mathematical model and experimental setup can be used later in the study of blades with more complex geometric and strength characteristics or in cases when the real boundary conditions or mechanical characteristics of material are uncertain.

In this study, exergy efficiency calculations of a turboprop engine were performed together with main performance parameters such as shaft power, specific fuel consumption, fuel flow, thermal efficiency etc., for a range of flight altitude (0–14 km) and flight speeds (0–0.6 Mach). A novel exergy efficiency formula was derived in terms of specific fuel consumption and it is shown that these two parameters are inversely proportional to each other. Moreover, a novel exergy efficiency and thermal efficiency relation was also derived. The relationship showed that these two parameters are linearly proportional to each other. Exergy efficiency of the turboprop engine was found to be in the range of 23–33%. Thermal efficiency of the turboprop engine was found to be around 25–35%. Exergy efficiency is higher at higher speeds and altitude where the specific fuel consumption is lower. Conversely, exergy efficiency of the engine is lower for lower speeds and altitude where the specific fuel consumption is higher.

Precooled engine is a highly expected solution to achieve supersonic transport. As the crucial component, heat exchangers protect other components from ultrahigh temperature. In traditional design methods, the nominal result is multiplied by a safety factor, whose selection entirely depends on experience, ensuring sufficient working margin to cope with fluctuation of parameters. For aero-engine, heat exchangers must work reliably with minimum weight. An advanced method of thermal optimization design with parameters’ fluctuation is proposed and proved to be effective by experimental verification. The heat transfer area can be quantitatively linked with the design confidence level, considering the coupling effect of various parameters’ fluctuation. The probability density distribution of heat transfer area has the characteristic of positive skewness distribution. With the increase of design confidence, the required heat transfer area is growing faster and faster. After optimization, the design of heat exchanger meets the requirements and the weight is effectively controlled.