scholarly journals Time-dependent prediction of the unsteady pressure near-field from an under-expanded jet

2014 ◽  
Author(s):  
Aldo Rona ◽  
Danilo Di Stefano ◽  
Alessandro Mancini ◽  
Edward Hall
Keyword(s):  
Near Field ◽  
Time Dependent ◽  
Unsteady Pressure

Experimental Investigation of a Single Stage Axial Flow Compressor With Controlled Diffusion Airfoils

1996 ◽  
Author(s):  
S. Pieper ◽  
J. Schulte ◽  
A. Hoynacki ◽  
H. E. Gallus
Keyword(s):  
Pressure Field ◽  
Flow Behavior ◽  
Measurement Techniques ◽  
Three Dimensional ◽  
Tip Clearance ◽  
Time Dependent ◽  
Suction Surface ◽  
Average Technique ◽  
Unsteady Pressure ◽  
Controlled Diffusion

In order to verify an inverse design concept for modern compressor bladings, a subsonic compressor front stage with IGV was investigated. One objective of the design was to survey the flow field in detail, with emphasis on 3D viscous and unsteady aspects of the flow. Therefore, the compressor was equipped with various steady and unsteady measurement techniques. Additionally, a compressor design was chosen that allows an extension up to three stages with regard to the investigation of multistage axial compressor flow behavior. Test results of the steady measurements are discussed for IGV, rotor, and stator flow at design conditions as well as the overall stage performance. The measurements of the steady flow behavior confirm the expected design performance and show the high potential of the controlled diffusion airfoil concept. Only at the side walls near hub and casing there are some differences between design and measurement due to the complex three dimensional flow. For the study of unsteady effects, detailed measurements using hot-wire probes, glue-on hot-films, and semiconductor pressure transducers were performed. All measurements are evaluated using the ensemble-average technique. The results show how the boundary layers of the inlet guide vanes and stator blades develop in a flow that is periodically disturbed by the rotor. Time-dependent pressure distributions at midspan of both stators are described. In addition, the unsteady pressure field at the casing above the rotor was investigated. The minimum wall pressure is located away from the blade suction surface. The effects of tip clearance flow on the performance are presented. The radial extent covers 15% span from the tip. At rotor exit, the unsteady pressure field and the time-dependent three-dimensional velocity vectors illustrate the salient features of the viscous flow associated with the rotor.

scholarly journals Computational investigation of cavity flow control using a passive device

2012 ◽  
Vol 116 (1176) ◽  
pp. 153-174 ◽  
Author(s):  
B. Khanal ◽  
K. Knowles ◽  
A. J. Saddington
Keyword(s):  
Flow Control ◽  
Near Field ◽  
Flow Analysis ◽  
Flow Visualisation ◽  
Complete Suppression ◽  
Detached Eddy Simulation ◽  
Mean Flow ◽  
Passive Device ◽  
Unsteady Pressure ◽  
Empty Cavity

Abstract In this paper, flow control effectiveness of a passive device in relation to open cavity flowfield is investigated computationally and compared with experimental work. Specifically the modification in the cavity flowfield due to the presence of a spoiler is studied in details to explain the physics behind the flow control effects. A combination of 2D and 3D flow visualisation tools are used to understand the flow behaviour inside the cavity and the quantitative analysis of the unsteady pressure fluctuations is also performed to assess the unsteady effects. Flow simulations with a turbulence model based on a hybrid RANS/LES (commonly known as Detached-Eddy Simulation (DES)) are used in this study. The time-mean flow visualisation clearly showed the presence of three dimensional effects inside the empty cavity whereas the 3D effects were found to diminish in the presence of a spoiler. In the unsteady flow analysis, near-field acoustic spectra were computed for empty cavity as well as cavity-with-spoiler cases. Study of unsteady pressure spectra for the cavity-with-spoiler case was found to record the complete suppression of the dominant tones in the presence of the spoiler. The analysis has indicated that the main reason behind this suppression is due to the inability of faintly energised vortical structures (faintly energised as a result of the extraction of turbulent kinetic energy by the spoiler) to maintain the unsteady flapping of the separated shear layer.

scholarly journals Calculations of near-field emissions in frequency-domain into time-dependent data with arbitrary wave form transient perturbations

2012 ◽  
Vol 1 (2) ◽  
pp. 26
Author(s):  
Y. Liu ◽  
B. Ravelo ◽  
J. Ben Hadj Slama
Keyword(s):  
Time Domain ◽  
Near Field ◽  
Wave Spectrum ◽  
Computational Method ◽  
Time Dependent ◽  
Dependent Data ◽  
Wave Form ◽  
Frequency Dependent ◽  
Transient Electromagnetic ◽  
The Time Domain

This paper is devoted on the application of the computational method for calculating the transient electromagnetic (EM) near-field (NF) radiated by electronic structures from the frequency-dependent data for the arbitrary wave form perturbations i(t). The method proposed is based on the fast Fourier transform (FFT). The different steps illustrating the principle of the method is described. It is composed of three successive steps: the synchronization of the input excitation spectrum I(f) and the given frequency data H0(f), the convolution of the two inputs data and then, the determination of the time-domain emissions H(t). The feasibility of the method is verified with standard EM 3D simulations. In addition to this method, an extraction technique of the time-dependent z-transversal EM NF component Xz(t) from the frequency-dependent x- and y- longitudinal components Hx(f) and Hy(f) is also presented. This technique is based on the conjugation of the plane wave spectrum (PWS) transform and FFT. The feasibility of the method is verified with a set of dipole radiations. The method introduced in this paper is particularly useful for the investigation of time-domain emissions for EMC applications by considering transient EM interferences (EMIs).

The use of Gaussian trend surfaces for modelling glacio-isostatic crustal rebound

2004 ◽  
Vol 40 (2) ◽  
pp. 175-179 ◽  
Author(s):  
P. Fretwell ◽  
I. R. Peterson ◽  
D. E. Smith
Keyword(s):  
Empirical Data ◽  
Near Field ◽  
Gaussian Function ◽  
Sea Surface ◽  
Time Dependent ◽  
Far Field ◽  
Trend Surface ◽  
Surface Level ◽  
Mathematical Solution ◽  
Better Than

SynopsisThe behaviour of the Earth's continental crust and mantle may be modelled as a buoyant floating plate on a viscous liquid, and the variations of load imposed by an ice sheet may be modelled as a time-dependent force. In recent work it has been shown that the mathematical solution of this problem can be subdivided into a propagating far-field forebulge term and a non-propagating near-field term. The latter often dominates and can be approximated satisfactorily by a generalized Gaussian function. Here we fit empirical data from the Main Postglacial Shoreline of northern Britain to a Gaussian trend surface. We show that the fit is significantly better than that of a polynomial trend surface previously published, and that the method has the potential to predict the likely sea surface level offshore at the zero isobase for the shoreline.

scholarly journals Time‐dependent wave‐vector analysis of the near‐field pressure of a fluid‐loaded cylinder

1991 ◽  
Vol 89 (4B) ◽  
pp. 1956-1956
Author(s):  
Gerard P. Carroll ◽  
Arthur B. Baggeroer ◽  
Edward K. Scheer
Keyword(s):  
Wave Vector ◽  
Near Field ◽  
Time Dependent ◽  
Vector Analysis

Asymptotic and Exact Radiation Boundary Conditions for Time-Dependent Scattering

1999 ◽  
Author(s):  
Lonny L. Thompson ◽  
Runnong Huan
Keyword(s):  
Cauchy Problem ◽  
Finite Element ◽  
Boundary Conditions ◽  
Near Field ◽  
Three Dimensions ◽  
Time Dependent ◽  
Radiation Boundary Condition ◽  
Radiation Boundary Conditions ◽  
First Order ◽  
Radiation Boundary

Abstract Asymptotic and exact local radiation boundary conditions first derived by Hagstrom and Hariharan are reformulated as an auxiliary Cauchy problem for linear first-order systems of ordinary equations on the boundary for each harmonic on a circle or sphere in two- or three-dimensions, respectively. With this reformulation, the resulting radiation boundary condition involves first-order derivatives only and can be computed efficiently and concurrently with standard semi-discrete finite element methods for the near-field solution without changing the banded/sparse structure of the finite element equations. In 3D, with the number of equations in the Cauchy problem equal to the mode number, this reformulation is exact. If fewer equations are used, then the boundary conditions form uniform asymptotic approximations to the exact condition. Furthermore, using this approach, we formulate accurate radiation boundary conditions for the two-dimensional unbounded problem on a circle. Numerical studies of time-dependent radiation and scattering are performed to assess the accuracy and convergence properties of the boundary conditions when implemented in the finite element method. The results demonstrate that the new formulation has dramatically improved accuracy and efficiency for time domain simulations compared to standard boundary treatments.

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