Arvind G. Rao

A hybrid engine concept for multi-fuel blended wing body

Purpose – The purpose of this paper is to present a novel hybrid engine concept for a multi-fuel blended wing body (MFBWB) aircraft and assess the performance of this engine concept. Design/methodology/approach – The proposed hybrid engine concept has several novel features which include a contra-rotating fan for implementing boundary layer ingestion, dual combustion chambers using cryogenic fuel (liquefied natural gas [LNG] or liquid hydrogen [LH2]) and kerosene in the inter-turbine burner (in flameless combustion mode) and a cooling system for bleed air cooling utilizing the cryogenic fuel. A zero-dimensional thermodynamic model of the proposed hybrid engine is created using Gas Turbine Simulation Program to parametrically analyse the performance of various possible engine architectures. Furthermore, the chosen engine architecture is optimized at a cycle reference point using a developed in-house thermodynamic engine model coupled with genetic algorithm. Findings – Using LH2 and kerosene, the hybrid eng...

Simulation of Reacting Spray in a Multi-Point Lean Direct Injection Combustor

This paper investigates the reacting spray phenomena in a multi-point lean direct injection (MPLDI) combustor to characterize the effects of highly swirling air flows on spray combustion. The Reynolds-averaged Navier Stokes (RANS) code is applied to simulate the turbulent, reacting, and swirling flow associated with the combustor. For the liquid spray modeling, several spray sub-models are used. Properties of both the gas and liquid phases are analyzed. The reacting flow simulations show short flames emanating from the individual injectors, uniformly low temperature distribution inside the combustor, and a uniform temperature profile at the chamber exit. With an increase in air flow velocity, the flow field becomes highly strained at the injector exits where the fuel and air streams mix and at the interfaces of the neighboring swirlers, allowing the mixing process to speed up. Overall, the computational results are able to capture and explain some of the fundamental features of the MPLDI combustor, such as the fuel-air mixing, drop size distribution, drop vaporization, and spray combustion process.

Conceptual Study of Future Aero-Engine Concepts

The soaring fuel price and the burgeoning environmental concerns have compelled global research towards cleaner engines, aimed at substantial reduction in emission, noise and fuel consumption. In this context, the present research investigates the feasibility of some novel engine concepts, namely Geared Turbofan and Intercooled Recuperated Turbofan concepts, by hypothetically applying them into an existing state-of-the-art high bypass ratio engine. This paper assesses the effects on the baseline engine performances due to the introduction of these two concepts in it. By performing steady state simulations, it was found that incorporation of the Geared Turbofan concept into the baseline Turbofan engine reduced thrust specific fuel consumption, engine weight, and fan blade tip speed. However, when simulations were carried out by incorporating the Intercooler and Recuperator concept in the baseline turbofan engine, it did not demonstrate any substantial improvement in fuel consumption. It was observed that the engine performance was influenced to a large extent by the heat exchanger’s effectiveness and the associated pressure drop. In addition, the overall engine weight increased due to the inclusion of massive heat exchangers necessary for intercooling and recuperating.

HEAT TRANSFER INVESTIGATIONS IN MULTIPLE IMPINGING JETS AT LOW REYNOLDS NUMBER

Jet impingement is a well established cooling methodology used for cooling turbine blades in gas turbine engines. Jet impingement results in high heat transfer coefficients as compared to other conventional modes of single phase heat transfer.

Conceptual Study of a Hybrid Turbofan Engine With Inter Turbine Burner

Most of the improvement in aviation during the last 7 decades has been mainly due to the advancement in the propulsion systems and technologies. The Advisory Council for Aeronautics Research in Europe (ACARE) has set ambitious objectives to be completed by 2020 and beyond; the major being reduction of CO2 emissions by more than 50%, for which significant improvement of the propulsion systems is required. However, it appears that a technological plateau has been reached with conventional engine architecture. The paper presents a novel hybrid engine architecture with inter turbine burner (ITB). The hybrid engine with two combustion chambers offers the possibility of operating on hydrocarbon fuels as well as liquid hydrogen, enabling the aimed reduction of CO2 emissions by 50% without encountering the storage problems related to pure hydrogen powered aircraft.Copyright

Infrared Signature Modeling and Analysis of Aircraft Plume

Abstract In recent years, the survivability of an aircraft has been put to task more than ever before. One of the main reasons is the increase in the usage of Infrared (IR) guided Anti-Aircraft Missiles, especially due to the availability of Man Portable Air Defence System (MANPADS) with some terrorist groups. Thus, aircraft IR signatures are gaining more importance as compared to their radar, visual, acoustic, or any other signatures. The exhaust plume ejected from the aircraft is one of the important sources of IR signature in military aircraft that use low bypass turbofan engines for propulsion. The focus of the present work is modelling of spectral IR radiation emission from the exhaust jet of a typical military aircraft and to evaluate the aircraft susceptibility in terms of the aircraft lock-on range due to its plume emission, for a simple case against a typical Surface to Air Missile (SAM). The IR signature due to the aircraft plume is examined in a holistic manner. A comprehensive methodology of computing IR signatures and its affect on aircraft lock-on range is elaborated. Commercial CFD software has been used to predict the plume thermo-physical properties and subsequently an in-house developed code was used for evaluating the IR radiation emitted by the plume. The LOWTRAN code has been used for modeling the atmospheric IR characteristics. The results obtained from these models are in reasonable agreement with some available experimental data. The analysis carried out in this paper succinctly brings out the intricacy of the radiation emitted by various gaseous species in the plume and the role of atmospheric IR transmissivity in dictating the plume IR signature as perceived by an IR guided SAM.

Numerical Study of Non-Reacting and Reacting Flow Characteristics in a Lean Direct Injection Combustor

The Lean Direct Injection (LDI) combustion concept has been of active interest due to its potential for low emissions under a wide range of operational conditions. This might allow the LDI concept to become the next generation gas-turbine combustion scheme for aviation engines. Nevertheless, the underlying unsteady phenomena, which are responsible for low emissions, have not been widely investigated. This paper reports a numerical study on the characteristics of the non-reacting and reacting flow field in a single-element LDI combustor. The solution for the non-reacting flow captures the essential aerodynamic flow characteristics of the LDI combustor, such as the reverse flow regions and the complex swirling flow structures inside the swirlers and in the neighborhood of the combustion chamber inlet, with reasonable accuracy. A spray model is introduced to simulate the reacting flow field. The reaction of the spray greatly influences the gas-phase velocity distribution. The heat release effect due to combustion results in a significantly stronger and compact reverse flow zone as compared to that of the non-reacting case. The inflow spray is specified by the Kelvin-Helmholtz breakup model, which is implemented in the Reynolds-Averaged Navier Stokes (RANS) code. The results show a strong influence of the high swirling flow field on liquid droplet breakup and flow mixing process, which in turn could explain the low-emission behavior of the LDI combustion concept.Copyright

Emission Modeling of an Interturbine Burner Based on Flameless Combustion

Since its discovery, the flameless combustion (FC) regime has been a promising alternative to reduce pollutant emissions of gas turbine engines. This combustion mode is characterized by well-distributed reaction zones, which potentially decreases temperature gradients, acoustic oscillations, and NOx emissions. Its attainment within gas turbine engines has proved to be challenging because previous design attempts faced limitations related to operational range and combustion efficiency. Along with an aircraft conceptual design, the AHEAD project proposed a novel hybrid engine. One of the key features of the proposed hybrid engine is the use of two combustion chambers, with the second combustor operating in the FC mode. This novel configuration would allow the facilitation of the attainment of the FC regime. The conceptual design was adapted to a laboratory scale combustor that was tested at elevated temperature and atmospheric pressure. In the current work, the emission behavior of this scaled combustor is analyzed using computational fluid dynamics (CFD) and chemical reactor network (CRN). The CFD was able to provide information with the flow field in the combustor, while the CRN was used to model and predict emissions. The CRN approach allowed the analysis of the NOx formation pathways, indicating that the prompt NOx was the dominant pathway in the combustor. The combustor design can be improved by modifying the mixing between fuel and oxidizer as well as the split between combustion and dilution air.

Numerical Investigations on the Conceptual Design of a Ducted Contra-Rotating Fan

The Advisory Council for Aeronautics Research in Europe (ACARE) has set an ambitious array of objectives to be accomplished by 2050. It is often claimed that complying with those targets will not require evolution but, rather, revolution. If the growth in aviation has to be sustained in the future then we must come up with radical aircraft and engine configurations which can meet the demands of future aviation.The contra-rotating fan is one such system which can play an important role in the future engine configurations, such as the hybrid engine configuration that is being investigated in the EU cofounded AHEAD project.In order to design a CRF system, a 1-D code has been developed based on the inverse Blade Element Method (BEM) to design a contra rotating fan. The CRF design obtained from this methodology is then analyzed with a full 3D RANS simulation.The numerical analysis revealed that the performance of the first rotor satisfies with the given design requirements in terms of both pressure ratio and isentropic efficiency, thus proving the efficacy of using the 1-D code for designing the CRF. However, the performance of the rear rotor does not reach the design demands. It was observed that there is a strong flow separation around the root and a strong normal shock in the blade passage near the tip. It was found that there is a great difference between the blade metal inlet angles and the relative flow inlet angles near the root of the rear rotor. One of the main reasons for this is the calculation of the axial velocity depending on the vortex design and the resolution of the radial equilibrium. Based on the CFD simulations, the design code could be further modified to improve the design of CRF.© 2014 ASME

Study of Shock Wave Control by Suction & Blowing on a Highly-loaded Transonic Compressor Cascade

Abstract A numerical investigation of shock wave control over a highly-loaded transonic compressor blade is presented in the current work. Two types of active flow control methods, namely blowing and suction, are employed. Their effectiveness in controlling the shock wave boundary layer interaction in the intended cascade passage has been investigated numerically. The three-dimensional RANS equations in Cartesian coordinate system are solved using the cell-centred control volume approach. Blowing and suction at four locations along the blade are simulated. Aerodynamic performance is evaluated for each case in terms of total pressure recovery coefficient, deviation angle, etc. Results show that blowing is not capable of providing desired control outcome, as the effects can only be seen in the neighbourhood of the blowing slot. The reconfiguration of shock waves in cascade is realized by suction through the slots located downstream after shock waves. Both the right branch of leading edge shock and the passage shock wave move downstream toward the suction slot. Compared with the baseline case, the suction with a suction ratio of 1.2% from slot D (at the 51% Chord) increased the total pressure recovery coefficient by 10%, and decreased the deviation angle by 5°.