scholarly journals Mitigation of divertor heat flux by high-frequency ELM pacing with non-fuel pellet injection in DIII-D

2017 ◽  
Vol 12 ◽  
pp. 1030-1036 ◽  
Author(s):  
A. Bortolon ◽  
R. Maingi ◽  
D.K. Mansfield ◽  
A. Nagy ◽  
A.L. Roquemore ◽  
...  
Keyword(s):  
Heat Flux ◽  
High Frequency ◽  
Fuel Pellet ◽  
Pellet Injection

scholarly journals Factors of boreal summer latent heat flux variations over the tropical western North Pacific

2021 ◽  
Author(s):  
Yuqi Wang ◽  
Renguang Wu
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
North Pacific ◽  
High Frequency ◽  
Western North Pacific ◽  
Surface Wind ◽  
Low Frequency ◽  
Boreal Summer ◽  
Wind Intensity ◽  
Tropical Western North Pacific

AbstractSurface latent heat flux (LHF) is an important component in the heat exchange between the ocean and atmosphere over the tropical western North Pacific (WNP). The present study investigates the factors of seasonal mean LHF variations in boreal summer over the tropical WNP. Seasonal mean LHF is separated into two parts that are associated with low-frequency (> 90-day) and high-frequency (≤ 90-day) atmospheric variability, respectively. It is shown that low-frequency LHF variations are attributed to low-frequency surface wind and sea-air humidity difference, whereas high-frequency LHF variations are associated with both low-frequency surface wind speed and high-frequency wind intensity. A series of conceptual cases are constructed using different combinations of low- and high-frequency winds to inspect the respective effects of low-frequency wind and high-frequency wind amplitude to seasonal mean LHF variations. It is illustrated that high-frequency wind fluctuations contribute to seasonal high-frequency LHF only when their intensity exceeds the low-frequency wind speed under which there is seasonal accumulation of high-frequency LHF. When high-frequency wind intensity is smaller than the low-frequency wind speed, seasonal mean high-frequency LHF is negligible. Total seasonal mean LHF anomalies depend on relative contributions of low- and high-frequency atmospheric variations and have weak interannual variance over the tropical WNP due to cancellation of low- and high-frequency LHF anomalies.

Effects of high-frequency activity on latent heat flux of MJO

2018 ◽  
Vol 52 (3-4) ◽  
pp. 1471-1485 ◽  
Author(s):  
Yingxia Gao ◽  
Pang-Chi Hsu ◽  
Tim Li
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
High Frequency ◽  
High Frequency Activity

Time-Resolved Heat Transfer and Surface Pressure Measurements for a Fully Cooled Transonic Turbine Stage

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Jeremy B. Nickol ◽  
Randall M. Mathison ◽  
Malak F. Malak ◽  
Rajiv Rana ◽  
Jong S. Liu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Field ◽  
Surface Pressure ◽  
High Frequency ◽  
Gas Turbines ◽  
Pressure Measurements ◽  
Turbine Stage ◽  
Cooling Flow ◽  
Blade Cooling

The flow field in axial gas turbines is driven by strong unsteady interactions between stationary and moving components. While time-averaged measurements can highlight many important flow features, developing a deeper understanding of the complicated flows present in high-speed turbomachinery requires time-accurate measurements that capture this unsteady behavior. Toward this end, time-accurate measurements are presented for a fully cooled transonic high-pressure turbine stage operating at design-corrected conditions. The turbine is run in a short-duration blowdown facility with uniform, radial, and hot streak vane-inlet temperature profiles as well as various amounts of cooling flow. High-frequency response surface pressure and heat-flux instrumentation installed in the rotating blade row, stator vane row, and stationary outer shroud provide detailed measurements of the flow behavior for this stage. Previous papers have reported the time-averaged results from this experiment, but this paper focuses on the strong unsteady phenomena that are observed. Heat-flux measurements from double-sided heat-flux gauges (HFGs) cover three spanwise locations on the blade pressure and suction surfaces. In addition, there are two instrumented blades with the cooling holes blocked to isolate the effect of just blade cooling. The stage can be run with the vane and blade cooling flow either on or off. High-frequency pressure measurements provide a picture of the unsteady aerodynamics on the vane and blade airfoil surfaces, as well as inside the serpentine coolant supply passages of the blade. A time-accurate computational fluid dynamics (CFD) simulation is also run to predict the blade surface pressure and heat-flux, and comparisons between prediction and measurement are given. It is found that unsteady variations in heat-flux and pressure are stronger at low to midspan and weaker at high span, likely due to the impact of secondary flows such as the tip leakage flow. Away from the tip, it is seen that the unsteady fluctuations in pressure and heat-flux are mostly in phase with each other on the suction side, but there is some deviation on the pressure side. The flow field is ultimately shown to be highly three-dimensional, as the movement of high heat transfer regions can be traced in both the chord and spanwise directions. These measurements provide a unique picture of the unsteady flow physics of a rotating turbine, and efforts to better understand and model these time-varying flows have the potential to change the way we think about even the time-averaged flow characteristics.

3D Heat Transfer Assessment of Full-Scale Inlet Vanes With Surface-Optimized Film Cooling: Part 1 — Experimental Results

2019 ◽  
Author(s):  
R. J. Anthony ◽  
J. P. Clark ◽  
J. Finnegan ◽  
J. J. Johnson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Frequency ◽  
Film Cooling ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Full Scale ◽  
Pressure Side ◽  
Flux Measurements ◽  
Real Hardware

Abstract Full-scale annular experimental evaluation of two different high pressure turbine first stage vane cooling designs was carried out using high frequency surface heat-flux measurements in the Turbine Research Facility at the Air Force Research Laboratory. A baseline film cooling geometry was tested simultaneously with a genetically optimized vane aimed to improve efficiency and part life. Part 1 of this two-part paper describes the experimental instrumentation, test facility, and surface heat flux measurements used to evaluate both cooling schemes. Part 2 of this paper describes the result of companion conjugate heat transfer posttest predictions, and gives numerical background on the design and modelling of both film cooling geometries. Time-resolved surface heat flux data is captured at multiple airfoil span and chord locations for each cooling design. Area based assessment of surface flux data verifies the genetic optimization redistributes excessive cooling away from midspan areas to improve efficiency. Results further reveal key discrepancies between design intent and real hardware behavior. Elevated heat flux above intent in some areas led to investigation of backflow margin and unsteady hot gas ingestion at certain film holes. Analysis shows areas toward the vane inner and outer endwalls of the aft pressure side were more sensitive to reduced aft cavity backflow margin. In addition, temporal analysis shows film cooled heat flux having large high frequency fluctuations that can vary across nearly the full range of film cooling effectiveness at some locations. Velocity and acceleration of these large unsteady heat flux events moving near the endwall of the vane pressure side is reported for the first time. The temporal nature of the unsteady 3-D film cooling features are a large factor in determining average local heat flux levels. This study determined this effect to be particularly important in areas on real hardware along the HPT vane pressure side endwalls towards the trailing edge, where numerical assumptions are often challenged. Better understanding of the physics of the highly unsteady 3D film cooled flow features occurring in real hardware is necessary to accurately predict distress progression in localized areas, prevent unforeseen part failures, and enable improvements to turbine engine efficiency. The results of this two-part paper are relevant to engines in extended service today.

scholarly journals Влияние градиента концентрации плазмы на возбуждение ионно-циклотронных колебаний в омических разрядах токамака ТУМАН-3М

2019 ◽  
Vol 45 (18) ◽  
pp. 27
Author(s):  
А.А. Белокуров ◽  
Г.И. Абдуллина ◽  
Л.Г. Аскинази ◽  
Н.А. Жубр ◽  
В.А. Корнев ◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Density Gradient ◽  
Initial Level ◽  
Fuel Pellet ◽  
Plasma Parameters ◽  
Cyclotron Instability ◽  
Ion Cyclotron ◽  
Pellet Injection ◽  
Magnetic Probes ◽  
Excitation Conditions

In TUMAN-3M tokamak ohmic hydrogen and deuterium discharges oscillations with ion cyclotron (IC) frequency were detected. Fast magnetic probes poloidal array in TUMAN-3M is capable of detecting several harmonics of IC frequency of main plasma isotope. Fuel pellet injection significantly reduces IC oscillations intensity, though after complete pellet evaporation returns to initial level. IC oscillations localization and excitation conditions are of certain interest. Based on drift-cyclotron instability excitation theory and numerical modeling of scenarios with ohmic LH-transition and pellet-injection plasma parameters (density gradient primarily) effect on IC oscillations excitation was studied.

Pellet triggering of edge localized modes in low collisionality pedestals at DIII-D

2021 ◽  
Author(s):  
Robert S Wilcox ◽  
Larry R Baylor ◽  
Alessandro Bortolon ◽  
M Knölker ◽  
C J Lasnier ◽  
...  
Keyword(s):  
Heat Flux ◽  
Stability Boundary ◽  
Localized Modes ◽  
Energy Fluence ◽  
Alpha Emission ◽  
Large Pressure ◽  
Peak Heat Flux ◽  
Edge Localized Modes ◽  
Pellet Injection ◽  
Infrared Cameras

Abstract Edge localized modes (ELMs) are triggered using deuterium pellets injected into plasmas with ITER-relevant low collisionality pedestals, and the resulting peak ELM energy fluence is reduced by approximately 25-50% relative to natural ELMs destabilized at similar pedestal pressures. Cryogenically frozen deuterium pellets are injected from the low-field side of the DIII-D tokamak at frequencies lower than the natural ELM frequency, and heat flux is measured by infrared cameras. Ideal MHD pedestal stability calculations show that without pellet injection, these low collisionality pedestals were limited by their current density (peeling-limited) rather than their pressure gradient (ballooning-limited). ELM triggering success correlates strongly with pellet mass, consistent with the theory that a large pressure perturbation is required to trigger an ELM in low collisionality discharges that are far from the ballooning stability boundary. For sufficiently large pellets, both instantaneous and time-integrated ELM energy deposition measured by infrared cameras is reduced with respect to naturally occurring ELMs at the inner strike point, which is the position where it is largest for natural ELMs. Energy fluence at the outer strike point is less effected. Cameras observing both heat flux and D-alpha emission often find significant toroidally asymmetric striations in the outboard far scrape-off layer resulting from ELMs that are triggered by pellets. Toroidal asymmetries at the inner strike point are similar between natural and pellet-triggered ELMs, suggesting that the reduction in peak heat flux and total fluence at that location is robust for the conditions reported here.

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