Multi-Stage Nozzle-Shape Optimization For Pulsed Hydrogen-Air Detonation Combustor

hermal engines based on pressure gain combustion offer new opportunities to generate thrust with enhanced efficiency and relatively simple machinery. The sudden expansion of detonation products from a single-opening tube yields thrust, although this is suboptimal. In this article, we present the complete design optimization strategy for nozzles exposed to detonation pulses, combining unsteady Reynolds-averaged Navier-Stokes solvers with the accurate modeling of the combustion process. The parameterized shape of the nozzle is optimized using a differential evolution algorithm to maxi­ mize the force at the nozzle exhaust. The design of experiments begins with a first optimization considering steady-flow conditions, subsequently followed by a refined optimization for transient supersonic flow pulse. Finally, the optimized nozzle performance is assessed in three dimensions with unsteady Reynolds-averaged Navier-Stokes capturing the deflagration-to-detonation transition of a stoichiometric, premixed hydrogen-air mixture. The optimized nozzle can deliver 80% more thrust than a standard detonation tube and about 2% more than the optimized results assuming steady-flow operation. This study proposes a new multi-fidelity approach to optimize the design of nozzles exposed to transient operation, instead of the traditional methods proposed for steady-flow operation

H2020 STRATOFLY Project: from Europe to Australia in less than 3 hours

As eluded in previous studies, with special reference to those carried out in the European framework, some innovative high-speed aircraft configurations have now the potential to assure an economically viable high-speed aircraft fleet. They make use of unexploited flight routes in the stratosphere, offering a solution to the presently congested flight paths while ensuring a minimum environmental impact in terms of emitted noise and green-house gases, particularly during stratospheric cruise. However, only a dedicated multi-disciplinary integrated design approach could realize this, by considering airframe architectures embedding the propulsion systems as well as meticulously integrating crucial subsystems. In this context, starting from an in-depth investigation of the current status of the activities, the STRATOFLY project has been funded by the European Commission, under the framework of Horizon 2020 plan, with the aim of assessing the potential of this type of high-speed transport vehicle to reach Technology Readiness Level (TRL) 6 by 2035, with respect to key technological, societal and economical aspects. This paper aims at summarizing the main results achieved so far to solve the main issues related to thermal and structural integrity, low-emissions combined propulsion cycles, subsystems design and integration, including smart energy management, environmental aspects impacting climate change, noise emissions and social acceptance, and economic viability accounting for safety and human factors

Turbine Base Pressure Active Control Through Trailing Edge Blowing

The desire for high performance and low fuel consumption aero-engines has been pushing the limits of the turbomachinery and leading cutting-edge engine designs to fulfill the demand. The number of stages is reduced to achieve the same pressure ratios over lighter turbines. The extreme expansion requirements result in transonic-supersonic flow fields. Transonic and supersonic turbines are exposed to the shock waves that appear at the trailing edge of the airfoils, generating substantial efficiency deduction due to the interaction with the boundary layer. Furthermore, pressure fluctuations created by the shocks result in unsteady forcing on downstream components and eventually cause high cycle fatigue. Component failure may lead reduced service life and further damage on the engine. A novel proposal to control the resulting fish tail shock waves consists on, pulsating coolant blowing through the trailing edge of the airfoils. The changes in the base region topology and fish tail shock wave were numerically investigated for a wide range of purge flow at simplified blunt and circular trailing edge geometries. An optimum purge rate which increases the base pressure and significantly reduces the trailing edge shock wave intensity was found. The effects of pulsating base pressure on the shock properties and the base region was investigated in detail to understand the mechanisms driving the flow field under unsteady bleed. A linear cascade representative of modern turbine bladings was specifically designed and constructed. The test matrix comprised four Mach numbers, from subsonic to supersonic regimes (0.8, 0.95, 1.1 and 1.2) together with two engine representative Reynolds numbers (4 and 6 million) at various blowing rates. The blade loading, the downstream pressure distributions and the unsteady wall temperature measurements allowed understanding the effects on each leg of the shock structure. Minimum shock intensities were achieved using pulsating cooling. A substantial increase in base pressure and significant reduction in trailing edge loss were observed for low coolant blowing rate. Analysis of the high frequency Schlieren pictures revealed the modulation of the shock waves with the coolant pulsation. The Strouhal number of the vortex shedding was analyzed for all of the conditions. Finally, the statistical analyses of the results showed that the effects of the state of cooling and free stream conditions were statistically significant on the flow properties

Development of a robust solver to model the flow inside the engines for high-speed propulsion

The demand for discovering new commercial routes as well as the possibility to shortening civilian long-haul flights boosted the interest of civil hypersonic vehicle designs. Among all the multiple projects started by the various nations, the European community funded project STRATOFLY aims at refining the baseline LAPCAT II-MR2.4 design for further improvements. The new aircraft would enable a flight shorter that 3 hours from Brussels to Sydney, carrying 300-passengers above the already crowed atmosphere. The wide Mach range operability, up to Mach 8, demands the use of multiple engines, leading to a highly integrated propulsion system. The current study is focused on the development of new CFD platform to estimate the performance of the combined propulsion system during the supersonic to hypersonic transition. In order to control the complex flow physics, highfidelity CFD simulations remain the fundamental tools for the preliminary investigations. On the current framework, an advanced robust compressible solver has been develop d in order to handle the different flow regimes. The new tool solves Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations by employing cell-centered Finite Volume Method constructed on openFoam toolbox. Two innovative high-order discretization schemes, with different abilities, based on approximated Riemann solvers were developed for capturing the flow physics within high-speed propulsion systems. Advanced time discretization has been taken into account to increase the temporal accuracy. At the end, the whole implementation has been validated in multiple test cases, ranging from incompressible to hypersonic regimes, confirming its excellent stability, robustness and accuracy

Mitigation of Turbine Vane Shock Waves Through Trailing Edge Cooling

The immense market demand on the high efficiency and lightweight aero-engines results in designs with compact high-pressure turbine stages experiencing supersonic flow field. In supersonic turbines, shocks appear at the vane trailing edges. The interaction of these shock with the neighbouring airfoils and blades on the adjacent rotor row and consequently create considerable amount of losses on the aerodynamic performance of the turbine. Moreover, periodic excitation created by the interaction of the shock waves and the motion of the turbine rotor causes fatigue problems and reduces the lifetime of the engine. Current study aims to alter the vane shock waves through blowing at the trailing edge. In order to characterize the effect of active blowing on the trailing edge flow field, a series of URANS simulations were conducted on OpenFOAM solver platform. Various blowing schemes were simulated over a simplified trailing edge geometry exposed in supersonic flow. The computations were compared in terms of shock intensity, oscillation frequency and exerted pressure forcing over the downstream components. The results showed that unsteady trailing edge blowing were able to modify the fluctuations observed on the shocks by altering the shock intensity, angle and frequency of oscillations. The classification of the wake unsteadiness, i.e. vortex shedding, in terms of trailing edge characteristics were also accomplished through frequency domain analysis of simulations

Mitigation of Turbine Vane Shock Waves Through Trailing Edge Cooling

The immense market demand on the high efficiency and lightweight aero-engines results in designs with compact high-pressure turbine stages experiencing supersonic flow field. In supersonic turbines, shocks appear at the vane trailing edges. The interaction of these shock with the neighbouring airfoils and blades on the adjacent rotor row and consequently create considerable amount of losses on the aerodynamic performance of the turbine. Moreover, periodic excitation created by the interaction of the shock waves and the motion of the turbine rotor causes fatigue problems and reduces the lifetime of the engine. Current study aims to alter the vane shock waves through blowing at the trailing edge. In order to characterize the effect of active blowing on the trailing edge flow field, a series of URANS simulations were conducted on OpenFOAM solver platform. Various blowing schemes were simulated over a simplified trailing edge geometry exposed in supersonic flow. The computations were compared in terms of shock intensity, oscillation frequency and exerted pressure forcing over the downstream components. The results showed that unsteady trailing edge blowing were able to modify the fluctuations observed on the shocks by altering the shock intensity, angle and frequency of oscillations. The classification of the wake unsteadiness, i.e. vortex shedding, in terms of trailing edge characteristics were also accomplished through frequency domain analysis of simulations

Energy Analysis of Pulsating Coolant Ejection

High-pressure turbines are subjected to high expansion ratios which may result in supersonic vane or rotor outlet. In the supersonic regime, shock waves are formed at the vane trailing edges that periodically impact on the downstream rotor blades and the neighboring vane. Pulsating cooling was proposed to modulate the trailing edge shocks to diminish the detrimental efficiency abatement and structural problems. A large test section equipped with three airfoils, replicated the actual loading of a transonic vane. Tests were performed in a short duration compression tube facility at four Mach numbers (0.8, 0.95, 1.1 and 1.2) and two different Reynolds numbers (4 and 6 million). Coolant was fed to the trailing edge of the central airfoil through a siren valve, that allowed to study four different coolant blowing cases: no-blowing, continuous blowing at three pressure levels and a pulsating coolant blowing condition. Unsteady numerical simulations of the flow over the airfoil model were performed using ANSYS 14 (Fluent) flow solver. In order to understand the impact of the different steady and unsteady cooling schemes on the efficiency of high pressure turbine bladings, the individual contribution of trailing edge and profile losses were calculated. The coolant ejection generated a significant reduction of the trailing edge loss. The overall losses also diminished by the introduction of cooling as compared to no blowing case. Improvements in loss levels owing to pulsating cooling observed to be more pronounced for the engine representative cooling rates (∼3%). The trends in loss variation with respect to cooling scheme show that pulsating cooling may become superior for high blowing cases

Analysis of a combined cycle propulsion system for STRATOFLY hypersonic vehicle over an extended trajectory

Hypersonic civil aviation is an important enabler for extremely shorter flight durations for long-haul routes and using unexploited flight altitudes. Combined cycle engine concepts providing extended flight capabilities, i.e. propelling the aircraft from take-off to hypersonic speeds, are proposed to achieve high-speed civil air transportation. STRATOFLY project is a continuation of former European efforts in hypersonic research and aims at developing a commercial reusablevehicle for cruise speed of Mach 8 at stratospheric altitudes as high as 35 km above ground level. The propulsion plant of STRATOFLY aircraft consists of combination of two different type of engines: an array of air turbo rockets and a dualmode ramjet/scramjet. In the present study, 1D transient thermodynamic simulations for this combined cycle propulsion plant have been conducted between Mach 0 to 8 by utilizing 1D inviscid flow transport relations, numerical tools availablein EcosimPro software platform and the European Space Propulsion System Simulation libraries. The optimized engine parameters are achieved by coupling EcosimPro software with Computer Aided Design Optimization which is a differential evolution algorithm developed at the von Karman Institute

Reduced order design and investigation of intakes for high speed propulsion systems

Ramjet propulsion is commonly preferred to power supersonic and hypersonic vehicles for cruising faster than Mach 3. This is an elegant solution owing to the lean architecture which does not embody any rotating parts. Although the geometry of the engine is simple as compared to turbine based configurations, the flow physics through the engine duct is quite complex and the flow speeds modulate between the supersonic and subsonic regimes multiple times. The design and performance analysis of ramjet engines are vital to ensure that propulsion system can satisfy the flight trajectory requirements. Therefore, this study introduces a reduced order holistic approach for design and assessment of the flow development in high-speed propulsion systems composed of generic elements of ramjet/scramjet engine configurations. Accordingly, the intakes designed based on axisymmetric flow templates are used to provide the necessary freestream flow modulation prior to the isolator through which a normal shock assumption is applied. The resultant flow properties are utilized for the combustion module where the flow expansion within the combustor and nozzle components are computed based on 1D steady inviscid flow equations coupled with detailed chemistry approach and JANAF tables. The module was validated and verified with the experimental and numerical data obtained for a dual-mode ramjet/scramjet combustor. Consequently, the parameters such as thrust, fuel consumption and specific impulse are calculated to quantify the engine performance for each design. Finally, the employment of the low fidelity model is demonstrated over a family of ramjet flow paths where the design space is confined based on the requirements of a high-supersonic cruise vehicle

Thermodynamic efficiency analysis and investigation of exergetic effectiveness of STRATOFLY aircraft propulsion plant

info:eu-repo/semantics/publishe