A Computational Analysis of the Aerodynamics and Aeroacoustics of Jets with Fluid Injection

A detailed numerical analysis of fluidic injection as a tool to reduce noise emission is presented here. The noise reduction strategy, developed at the Pennsylvania State University, is based on injectors that blow air into the diverging section of the nozzle to emulate the effect of interior corrugation on the jet plume. The advantage is that the injection can be activated during takeoff and turned o_ during other phases of flight so that performance is not affected. Numerical simulations are performed on a military-style nozzle based on the GE F400-series engines, with a design Mach number of 1:65, for over-expanded jet conditions. The effectiveness of the fluidic injection as noise reduction technique is analyzed for heated and unheated jets. A high-order Large Eddy Simulation (LES) solver, developed originally at Purdue University, is used to analyze the flow-field and the acoustic field. New initial conditions and new boundary conditions are introduced. A set of Reynolds Averaged Navier-Stokes (RANS) simulations is used to set up the initial and boundary conditions for the LES runs. The numerical results are compared and validated with the outcome of experiments and RANS simulations performed at the Pennsylvania State University. The characteristics of unheated and heated jets are presented and compared. The higher temperatures do not modify the shock-cell structures, while they affect the jet development and the acoustic signature. The fluidic injection shows the potential of breaking down the shock-cells into smaller structures with lower strength, directly reducing the intensity of broadband shock associated noise. Moreover, the injectors are found to affect the development of the larger turbulent structures that generate the peak noise. For the cases tested the injectors reduce the peak noise by more than 1:5 dB for the unheated jet and by 3 dB for the heated jet, on the azimuthal plane in between two lines of injectors. The direction of maximum sound propagation moves from about 30_ to about 50_ as the jet gets heated. An analysis of the thrust changes due to activating the injectors is also presented for the heated and unheated jet conditions. The specific thrust is reduced by about 3% when the injectors are used

The role of economic and policy variables in energy-efficient retrofitting assessment. A stochastic Life Cycle Costing methodology

Abstract Energy saving is a major policy objective worldwide and in the EU in particular. Evaluating the convenience of energy-efficient investments, however, is complex. This paper aims to apply stochastic Life Cycle Costing to assess the economic value of energy-efficient building retrofitting investments. The proposed approach investigates how macroeconomic variables affect such an evaluation by explicitly taking into account their interdependent stochastic nature. Consequently, the economic evaluation of an investment is itself stochastic thus expressing both its expected value and its inherent uncertainty and risk. On this basis, an illustrative case-study is presented, where alternative designs of the energy-saving intervention are compared and a sensitivity analysis performed to identify the determinants of the LCC outcome and of its variability. In terms of policy implications, a tool providing a sounder evaluation of the convenience of such investments can suggest when and to what extent incentives may be appropriate to facilitate these investments and what possible financial instruments could be put forward in order to reduce the associated risk

Noise reduction analysis of supersonic unheated jets with fluidic injection using large eddy simulations

A set of large eddy simulations is used to perform a numerical analysis of fluidic injection as a tool for noise reduction. This technique, developed at the Pennsylvania State University, allows one to turn on and off the air injectors in order to reduce the noise during takeoff and landing without penalizing performance in other flight regimes. Numerical simulations are performed on a military-style nozzle based on the GE F400-series engines, with a design Mach number of 1.65, for overexpanded jet conditions. The numerical results are compared and validated with the outcome of experiments performed at the Pennsylvania State University. For the case chosen, the fluidic injection shows the potential of breaking down shock cells into smaller structures with different orientation and strength. This directly reduces the intensity of broadband shock associated noise, with a positive effect of reducing the overall sound pressure level by more than [Formula: see text] along the direction of maximum sound propagation of the baseline case. The maximum noise reduction was found to be almost [Formula: see text] at 55° on the azimuthal plane in between two lines of injectors. </jats:p