Transforming the shock pattern of supersonic jets using fluidic injection

Double shock diamonds establish in the exhaust of modular convergent-divergent nozzles. These consist of two shock structures; one originating from the nozzle throat and another from its exit. Analyzing the shock pattern developing for different fluidic injection operating conditions, it is shown that fluidic injection allows the rearrangement of the shock structures relative to each other. Overlapping the two structures caused large pressure oscillations in the exhaust and high amplitudes of shock associated noise, whereas staggering the shock structures mitigated these effects. The screech tone frequency did not change for all injection operating configurations, although the shock diamonds had been shifted drastically with respect to each other. Hence, the screech phenomenon is dominated by the primary shock spacing originating from the nozzle throat

Airframe installation effects on the jet exhausting a coaxial nozzle system of a gas turbine engine

Jet engine installation effects can significantly affect the behavior of the exhausting flow otherwise axisymmetric for an axial-symmetric nozzle configuration. Considering the problem associated solely with the turbulent jet (i.e. neglecting jet interaction with the airframe or the flight effects) has severe limitations on accurately predicting the real case scenario. It should also be emphasized that the major sources of noise for an aircraft are the high velocity, turbulent hot jets exhausting aircraft's gas turbine engines. Therefore, the prediction of the compressible jet by including wing and pylon effects represents today a topic of high interest in aeroacoustics. A numerical study is carried out for analyzing the flow associated with a separate flow nozzle system with and without installation effects. The Baseline case (without airframe installation) is compared with the case in which only the pylon is considered and with the case where the wing and the pylon are interfering with the jet engine. The simulations are performed with and without forward-flight effects. The tertiary flow increases the length of the potential core region while limiting the radial spread of the jet. The airframe installation effects increase the jet spreading underneath the pylon-nozzlewing assembly while lowering the production of turbulence in that region. Particle Imaging Velocimetry experimental flow data are used to validate the computational results for the Baseline and the Pylon cases without the forward-flight effects. Copyright © 2012 by ASME

Large Eddy Simulations of microjets impact on supersonic jet exiting a C-D conical nozzle

The effect of multiple microjets on the acoustic noise production originating from a supersonic jet exhausting a gas turbine engine is studied numerically using the Large Eddy Simulation (LES) approach. The nozzle exit design Mach-number is 1:56, while the total temperature ratio is kept to 1:27. The nozzle contour is a double cone converging- diverging nozzle. The emerging jet is slightly over-expanded. A double shock-diamond pattern develops in the supersonic flow. The study focuses on the changes in the flow pattern, the shock-associated noise and the radiated near-field acoustics when using fluidics as compared with a baseline, (i.e. without fluidics). Just downstream of the nozzle lip, twelve cylindrical microjets are placed circumfer- entially, with a 60° inclination angle towards the nozzle centerline axis, in the streamwise flow direction. The pressurized massow feeding the microjets is assumed to be initially at ambient conditions. The amount of pressurization is given as an Injection Pressure Ratio (IPR) and represents the investigation parameter. Acoustic based experiments performed at University of Cincinnati (UC) exhibited acoustic benefit when using the mentioned set-up for the microjets. However, the impact that injection had on the flow-field was diffcult to be quantified. Thus, LES calculations have been performed to analyze the compressible flow-fleld, the shock-structure alteration and thrust evaluations associated with the fluidics

Investigation of the surge phenomena in a centrifugal compressor using large eddy simulation

The flow through a ported shroud compressor of an automobile turbocharger is simulated using Large Eddy Simulations. Generally, the compressor is subjected to work within certain range of the mass-flow conditions. Reduction of the operation mass-flow below a certain minimum limit, leads to breakdown of the complete compressor operability. Flow reversal occurs in the compressor wheel, which results in amplification of velocity and pressure fluctuations. Consequentially, large vibratory stresses are induced into the blades under off-design condition and thereby affect the blade life duration detrimentally. The aim of this study is to understand the generation of flow-structures during extreme operable conditions (surge condition) in a centrifugal compressor. The investigation of the appearing flow-structures with the surge phenomenon is essential to explore new methods that improve the stability or the flow-operating regime of the compressor. The complete 360° compressor geometry is utilized in the computational simulations. Further, the transient sliding mesh technique is applied to account for an accurate prediction of the mesh motion and thus, the geometrical interaction between the impeller and the stationary diffuser. The numerical results are compared with available experimental measurements obtained under the same operating conditions (design and near-surge condition). The rotating stall instability is predicted using FFT data analysis. Furthermore, the numerical study captures the low frequency peak characterizing the global instability of the surge condition. Copyright © 2013 by ASME

Study of mixing in swirling turbulent jets

Large Eddy Simulation of swirling flows in a typical gas turbine burner has been carried out. The goal has been to study the effects of swirl number, inlet velocity profile, confining wall distance, Reynolds- and Schmidt-number effects on the flow and turbulent mixing. The results show that the inlet velocity profile, the confinement and the swirl have a substantial effect on the resulting flow-field, while the values of the Reynolds- and Schmidt-numbers are of less importance in our case