Pulse Distortion by Anisotropic Plasmas

1972 ◽  
Vol 50 (11) ◽  
pp. 1221-1223
Author(s):  
M. P. Bachynski ◽  
B. W. Gibbs
Keyword(s):  
Plasma Density ◽  
Strong Interaction ◽  
Incident Wave ◽  
Pulse Shape ◽  
Leading Edge ◽  
Experimental Measurements ◽  
Electromagnetic Pulses ◽  
Pulse Distortion ◽  
Maximum Penetration

Experimental measurements have been performed of electromagnetic pulses transmitted through a plasma under conditions of strong interaction (strong heating of the electrons) between the incident wave and the plasma. Severe pulse distortion depending on the plasma density and pulse shape can occur. The leading edge of the pulse does not always show maximum penetration through the plasma.

scholarly journals Unsteady Gapwise Periodicity of Oscillating Cascaded Airfoils

1982 ◽  
Author(s):  
F. O. Carta
Keyword(s):  
Unsteady Flow ◽  
Fourier Coefficient ◽  
Phase Angle ◽  
Leading Edge ◽  
Experimental Measurements ◽  
Pressure Data ◽  
Linear Cascade ◽  
Aerodynamic Damping ◽  
The Stability ◽  
Interblade Phase Angle

Tests were conducted on a linear cascade of airfoils oscillating in pitch to measure the unsteady pressure response on selected blades along the leading edge plane of the cascade and over the chord of the center blade. The pressure data were reduced to Fourier coefficient form for direct comparison, and were also processed to yield integrated loads and, particularly, the aerodynamic damping coefficient. In addition, results from two unsteady theories for cascaded blades with nonzero thickness and camber were compared with the experimental measurements. The three primary results that emerged from this investigation were: (a) from the leading edge plane blade data, the cascade was judged to be periodic in unsteady flow over the range of parameters tested, (b) as before, the interblade phase angle was found to be the single most important parameter affecting the stability of the oscillating cascade blades, and (c) the real blade theory and the experiment were in excellent agreement for the several cases chosen for comparison.

scholarly journals Evaluation of CFD Predictions Using Thermal Field Measurements on a Simulated Film Cooled Turbine Blade Leading Edge

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Sibi Mathew ◽  
Silvia Ravelli ◽  
David G. Bogard
Keyword(s):  
Turbine Blade ◽  
Turbulence Model ◽  
Stokes Equations ◽  
Leading Edge ◽  
Experimental Measurements ◽  
Stagnation Line ◽  
Thermal Fields ◽  
Sst Model ◽  
Adiabatic Effectiveness ◽  
Blade Leading Edge

Computational fluid dynamics (CFD) predictions of film cooling performance for gas turbine airfoils are an important part of the design process for turbine cooling. Typically, industry relies on the approach based on Reynolds Averaged Navier Stokes equations, together with a two-equation turbulence model. The realizable k-ɛ (RKE) model and the shear stress transport k-ω (SST) model are recognized as the most reliable. Their accuracy is generally assessed by comparing to experimentally measured adiabatic effectiveness. In this study, the performances of the RKE and SST models were evaluated by comparing predicted and measured thermal fields in a turbine blade leading edge with three rows of cooling holes, positioned along the stagnation line and at ±25 deg. Predictions and measurements were done with high thermal conductivity models which simulated the conjugate heat transfer effects between the coolant flow and the solid. Particular attention was placed on the thermal fields along the stagnation line, and immediately downstream of the off-stagnation line row of holes. Conventional evaluations in terms of adiabatic effectiveness were also carried out. Predictions of coolant flows at the stagnation line were significantly different when using the two different turbulence models. For a blowing ratio of M = 2.0, the predictions with the SST model showed coolant jet separation at the stagnation line, while the RKE predictions showed no separation. Experimental measurements showed that there was coolant jet separation at the stagnation line, but the actual thermal fields obtained from experimental measurements were significantly different from that predicted by either turbulence model. Similar results were seen for predicted and measured thermal fields downstream of the off-stagnation row of holes.

Large Eddy Simulation of the Laminar Heat Transfer Augmentation on the Pressure Side of a Turbine Vane Under Freestream Turbulence

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Yousef Kanani ◽  
Sumanta Acharya ◽  
Forrest Ames
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Leading Edge ◽  
Transition To Turbulence ◽  
Experimental Measurements ◽  
Pressure Side ◽  
Freestream Turbulence ◽  
Heat Transfer Augmentation ◽  
Eddy Simulation ◽  
Large Eddy

Vane pressure side heat transfer is studied numerically using large eddy simulation (LES) on an aft-loaded vane with a large leading edge over a range of turbulence conditions. Numerical simulations are performed in a linear cascade at exit chord Reynolds number of Re = 5.1 × 105 at low (Tu ≈ 0.7%), moderate (Tu ≈ 7.9%), and high (Tu ≈ 12.4%) freestream turbulence with varying length scales as prescribed by the experimental measurements of Varty and Ames (2016, “Experimental Heat Transfer Distributions Over an Aft Loaded Vane With a Large Leading Edge at Very High Turbulence Levels,” ASME Paper No. IMECE2016-67029). Heat transfer predictions on the vane pressure side are in a very good agreement with the experimental measurements and the heat transfer augmentation due to the freestream turbulence is well captured. At Tu ≈ 12.4%, freestream turbulence enhances the Stanton number on the pressure surface without boundary layer transition to turbulence by a maximum of about 50% relative to the low freestream turbulence case. Higher freestream turbulence generates elongated structures and high-velocity streaks wrapped around the leading edge that contain significant energy. Amplification of the velocity streaks is observed further downstream with max rms of 0.3 near the trailing edge but no transition to turbulence or formation of turbulence spots is observed on the pressure side. The heat transfer augmentation at the higher freestream turbulence is primarily due to the initial amplification of the low-frequency velocity perturbations inside the boundary layer that persist along the entire chord of the airfoil. Stanton numbers appear to scale with the streamwise velocity fluctuations inside the boundary layer.

Evaluation of CFD Simulations of Film Cooling Performance in the Showerhead Region of a Turbine Vane Including Conjugate Effects

2012 ◽  
Author(s):  
Thomas E. Dyson ◽  
David G. Bogard ◽  
Sean D. Bradshaw
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Leading Edge ◽  
External Boundary ◽  
Experimental Measurements ◽  
Impingement Cooling ◽  
Heat Transfer Augmentation ◽  
Turbine Vane ◽  
Sst Turbulence Model ◽  
Investigate Heat Transfer

Computational simulations using RANS and the k-ω SST turbulence model were performed to complement experimental measurements of overall cooling effectiveness and adiabatic film effectiveness for a film cooled turbine vane airfoil. Particular attention was placed on the showerhead. The design made use of five rows of showerhead holes and a single gill row on both pressure and suction sides. The simulated geometry also included the internal impingement cooling configuration. Internal and external boundary conditions were matched to experiments using the same vane model. To correctly simulate conjugate heat transfer effects, the experimental vane model was constructed to match the Biot number for engine conditions. Computational predictions of the overall and adiabatic effectiveness were compared to experimental measurements from both the conducting vane and a model constructed from low conductivity foam. The results show that the k-ω SST RANS model over-predicts both adiabatic and overall effectiveness due in part to limited jet diffusion. The simulations were also used to investigate heat transfer augmentation, which is difficult to measure experimentally in the showerhead region. The results showed substantial augmentation of 1.5 or more over large portions of the leading edge, with many areas exceeding 2.0. However, the simulations also showed a reduction in heat transfer (i.e., hf/h0 < 1) for locations beneath the coolant jets. This result was likely due to Taw being an inappropriate driving temperature for separated jets.

Lattice QCD Results and Prospects

2003 ◽  
Vol 18 (supp01) ◽  
pp. 1-26
Author(s):  
Richard Kenway
Keyword(s):  
Standard Model ◽  
Lattice Qcd ◽  
Strong Interaction ◽  
Bound States ◽  
Leading Edge ◽  
Beyond The Standard Model ◽  
Quark Masses ◽  
The Standard Model ◽  
Quark Flavour ◽  
Computationally Intensive

In the Standard Model, quarks and gluons are permanently confined by the strong interaction into hadronic bound states. The values of the quark masses and the strengths of the decays of one quark flavour into another cannot be measured directly, but must be deduced from experiments on hadrons. This requires calculations of the strong-interaction effects within the bound states, which are only possible using numerical simulations of lattice QCD. These are computationally intensive and, for the past twenty years, have exploited leading-edge computing technology. In conjunction with experimental data from B Factories, over the next few years, lattice QCD may provide clues to physics beyond the Standard Model. These lectures provide a non-technical introduction to lattice QCD, some of the recent results, QCD computers, and the future prospects.

An Analytic Formulation of PMD-Induced Pulse Distortion

2015 ◽  
Vol 36 (4) ◽  
Author(s):  
Witold Bardyszewski ◽  
Michael Reimer ◽  
David Yevick
Keyword(s):  
Pulse Shape ◽  
Error Probability ◽  
Input Pulse ◽  
Polarization Mode Dispersion ◽  
Second Order ◽  
Mode Dispersion ◽  
Pulse Distortion ◽  
Order Expansion ◽  
Analytic Expression

AbstractWe systematically analyze the pulse distortion resulting from polarization mode dispersion (PMD) by deriving an analytic expression for the characteristic function of the system bit error probability (BEP) density in terms of the lowest-order moments of the Fourier transformed input pulse shape. We determine the range of validity of our technique, which implements a second-order expansion of the Jones matrix, by comparing our results for chirped and unchirped input pulses with direct numerical simulations. Our method may be easily applied to analyze the role of the first- and second-order PMD in the interference between adjacent pulses.

scholarly journals About the features of hypersonic flow past a yawed plate

2019 ◽  
Vol 487 (1) ◽  
pp. 24-27
Author(s):  
G. N. Dudin ◽  
V. Ya. Neyland
Keyword(s):  
Hypersonic Flow ◽  
Strong Interaction ◽  
Leading Edge ◽  
Transverse Coordinate ◽  
Trailing Edge ◽  
The Third ◽  
Flow Past ◽  
Flow Functions

The flow around the yawed plate in the regime of strong interaction is considered in the case when the pressure at its trailing edge is not constant, but changes along the transverse coordinate. It is shown that in the case of large transverse gradients of the induced pressure, the type of expansions of flow functions in the vicinity of the leading edge changes significantly and the third term of the expansions should be taken into account.

Average pulse shape model for leading edge timing with Ge(Li) coaxial detector

1990 ◽  
Vol 37 (3) ◽  
pp. 1248-1253 ◽  
Author(s):  
M.A. El-Wahab ◽  
A. El-Arabi ◽  
M.H. Battrawi
Keyword(s):  
Pulse Shape ◽  
Leading Edge ◽  
Shape Model ◽  
Coaxial Detector

Unsteady Aerodynamics and Gapwise Periodicity of Oscillating Cascaded Airfoils

1983 ◽  
Vol 105 (3) ◽  
pp. 565-574 ◽  
Author(s):  
F. O. Carta
Keyword(s):  
Unsteady Flow ◽  
Fourier Coefficient ◽  
Unsteady Aerodynamics ◽  
Leading Edge ◽  
Experimental Measurements ◽  
Pressure Data ◽  
Linear Cascade ◽  
Aerodynamic Damping ◽  
The Stability ◽  
Interblade Phase Angle

Tests were conducted on a linear cascade of airfoils oscillating in pitch to measure the unsteady pressure response on selected blades along the leading edge plane of the cascade and over the chord of the center blade. The pressure data were reduced to Fourier coefficient form for direct comparison and were also processed to yield integrated loads and, particularly, the aerodynamic damping coefficient. In addition, results from two unsteady theories for cascaded blades with nonzero thickness and camber were compared with the experimental measurements. The three primary results that emerged from this investigation were: (a) from the leading edge plane blade data, the cascade was judged to be periodic in unsteady flow over the range of parameters tested, (b) as before, the interblade phase angle was found to be the single most important parameter affecting the stability of the oscillating cascade blades, and (c) the real blade theory and the experiment were in excellent agreement for the several cases chosen for comparison.

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