Rough Wall and Near-hole Obstruction Effects on Film Cooling with and Without a Transverse Trench PDF Download
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Author: Ruwan Prasanna Somawardhana Publisher: ISBN: Category : Languages : en Pages : 204
Book Description
Significant degradation of adiabatic effectiveness can be caused by surface roughness and near-hole obstructions formed from deposition of contaminants. Since obstructions are a randomly occurring event, there are many variables to consider, namely shape, width, length, height, and position in relation to a film cooling hole. In addition to this, the level of overall surface roughness must also be considered. This study investigated these different variables on the suction side of a scaled-up turbine vane using cylindrical holes to determine what is important when considering surface roughness and obstructions. In addition, the use of a transverse trench was tested with a rough wall and near-hole obstructions and was found to be a method to mitigate a large part of the degrading effects caused by a rough surface and near-hole obstructions.
Author: Ruwan Prasanna Somawardhana Publisher: ISBN: Category : Languages : en Pages : 204
Book Description
Significant degradation of adiabatic effectiveness can be caused by surface roughness and near-hole obstructions formed from deposition of contaminants. Since obstructions are a randomly occurring event, there are many variables to consider, namely shape, width, length, height, and position in relation to a film cooling hole. In addition to this, the level of overall surface roughness must also be considered. This study investigated these different variables on the suction side of a scaled-up turbine vane using cylindrical holes to determine what is important when considering surface roughness and obstructions. In addition, the use of a transverse trench was tested with a rough wall and near-hole obstructions and was found to be a method to mitigate a large part of the degrading effects caused by a rough surface and near-hole obstructions.
Author: Katharine Lee Harrison Publisher: ISBN: Category : Languages : en Pages : 314
Book Description
Film cooling computations and experiments were performed to study heat transfer and adiabatic effectiveness for several geometries. Various assumptions commonly made in film cooling experiments were computationally simulated to test the validity of using these assumptions to predict the heat flux into conducting walls. The validity of these assumptions was examined via computational simulations of film cooling on adiabatic, heated, and conducting flat plates using the commercial code FLUENT. The assumptions were found to be reasonable overall, but certain regions in the domain suffered from poor predictions. Film cooling adiabatic effectiveness and heat transfer coefficients for axial holes embedded in a 1 [hole diameter] transverse trench on the suction side of a simulated turbine vane were experimentally investigated as well to determine the net heat flux reduction. Heat transfer coefficients were determined with and without upstream heating both with and without a tripped boundary layer approach flow. The net heat flux reduction for the trench was found to be much higher than for the baseline row of holes. Two transverse trench geometries and a baseline row of holes geometry were also simulated using FLUENT and the results were compared to experiments by Waye and Bogard (2006). Trends between simulated trench configurations and baseline cylindrical holes without a trench were found to be largely in agreement with experimental trends, suggesting that FLUENT can be used as a tool for studying new trench configurations.
Author: Robert Schroeder Publisher: ISBN: Category : Languages : en Pages :
Book Description
Gas turbines are heavily used for electricity generation and aircraft propulsion with a strong desire in both uses to maximize thermal efficiency while maintaining reasonable power output. As a consequence, gas turbines run at high turbine inlet temperatures that require sophisticated cooling technologies to ensure survival of turbine components. One such technology is film cooling with shaped holes, where air is withdrawn from latter stages of the compressor, is bypassed around the combustor, and is eventually ejected out holes in turbine component surfaces. Air ejected from these shaped holes helps maintain components at temperatures lower than flow from the combustor. Many studies have investigated different factors that influence shaped hole performance. However, no studies in open literature have investigated how cooling performance is affected by roughness along interior walls of the shaped hole. The effect of in-hole roughness on shaped hole film cooling was the focus of this research. Investigation of in-hole roughness effects first required the determination of behavior for a shaped hole with smooth walls. A public shaped hole, now used by other investigators as well, was designed with a diffused outlet having 7 degree expansion angles and an area ratio of 2.5. At low freestream turbulence intensity of 0.5%, film cooling adiabatic effectiveness for this smooth hole was found to peak at a blowing ratio of 1.5. Measurements of flowfields and thermal fields revealed causes of this behavior. Blowing ratio increases above 1.5 caused the jet from the smooth hole to penetrate higher into the surrounding mainstream, exhibit a stronger counter-rotating vortex pair, and have narrower contact with the wall than at lower blowing ratios. Experiments performed at high freestream turbulence intensity of 13% revealed dynamics of how freestream turbulence both diluted and laterally spread coolant. At the high blowing ratio of 3 the dilution and spreading were competing effects, such that elevated freestream turbulence did not cause a decrease in area-averaged effectiveness. At the blowing ratio of 1.5, high freestream turbulence caused area-averaged effectiveness to decrease 17% relative to the low freestream turbulence case. Film cooling performance was measured for the shaped hole geometry with several different configurations of in-hole roughness. At low freestream turbulence intensity, in-hole roughness caused decreases in area-averaged adiabatic effectiveness up to 61% relative to the smooth hole performance. These percent decreases in adiabatic effectiveness were more severe with increasing roughness levels and with increasing blowing ratios. Flowfield and thermal field measurements for the configuration with largest roughness size showed that the decrease in adiabatic effectiveness for rough holes as compared to smooth holes was due to thicker boundary layers along the interior walls of the cooling holes. The thicker boundary layers resulted in faster jet core flow, which in turn caused increased penetration of coolant into the mainstream and increased turbulence intensity inside the jet, with both leading to reduced adiabatic effectiveness. Detrimental effects of in-hole roughness persisted at the high freestream turbulence conditions as well.
Author: Ruwan Prasanna Somawardhana
Author: Ruwan Prasanna Somawardhana
Author: Katharine Lee Harrison
Author: 
Author: S. Stephen Papell
Author: S. Stephen Papell
Author: 
Author: Christopher A. Whitfield
Author: Kokichi Furuhama
Author: Robert Schroeder
Author: David Seager