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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: 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: Publisher: ISBN: Category : Languages : en Pages : 31
Book Description
The thermal efficiency of gas turbine systems depends largely on the turbine inlet temperature. Recent decades have seen a steady rise in the inlet temperature and a resulting reduction in fuel consumption. At the same time, it has been necessary to employ intensive cooling of the hot components. Among various cooling methods, film cooling has become a standard method for cooling of the turbine airfoils and combustion chamber walls. The University of Minnesota program is a combined experimental and computational study of various film-cooling configurations. Whereas a large number of parameters influence film cooling processes, this research focuses on compound angle injection through a single row and through two rows of holes. Later work will investigate the values of contoured hole designs. An appreciation of the advantages of compound angle injection has risen recently with the demand for more effective cooling and with improved understanding of the flow; this project should continue to further this understanding. Approaches being applied include: (1) a new measurement system that extends the mass/heat transfer analogy to obtain both local film cooling and local mass (heat) transfer results in a single system, (2) direct measurement of three-dimensional turbulent transport in a highly-disturbed flow, (3) the use of compound angle and shaped holes to optimize film cooling performance, and (4) an exploration of anisotropy corrections to turbulence modeling of film cooling jets.
Author: Thomas Earl Dyson Publisher: ISBN: Category : Languages : en Pages : 576
Book Description
This study focused on the improvement of film cooling for gas turbine vanes using both computational and experimental techniques. The experimental component used a matched Biot number model to measure scaled surface temperature (overall effectiveness) distributions representative of engine conditions for two new configurations. One configuration consisted of a single row of holes on the pressure surface while the other used numerous film cooling holes over the entire vane including a showerhead. Both configurations used internal impingement cooling representative of a 1st vane. Adiabatic effectiveness was also measured. No previous studies had shown the effect of injection on the mean and fluctuating velocity profiles for the suction surface, so measurements were made at two locations immediately upstream of film cooling holes from the fully cooled cooling configuration. Different blowing conditions were evaluated. Computational tools are increasingly important in the design of advanced gas turbine engines and validation of these tools is required prior to integration into the design process. Two film cooling configurations were simulated and compared to past experimental work. Data from matched Biot number experiments was used to validate the overall effectiveness from conjugate simulations in addition to adiabatic effectiveness. A simulation of a single row of cooling holes on the suction side also gave additional insight into the interaction of film cooling jets with the thermal boundary layer. A showerhead configuration was also simulated. The final portion of this study sought to evaluate the performance of six RANS models (standard, realizable, and renormalization group k-[epsilon]; standard k-[omega]; k-[omega] SST; and Transition SST) with respect to the prediction of thermal boundary layers. The turbulent Prandtl number was varied to test a simple method for improvement of the thermal boundary layer predictions.
Author: Ahmad Mahmoud Alameldin Publisher: ISBN: Category : Aircraft gas-turbines Languages : en Pages : 144
Book Description
Abstract: Gas turbines are a major contributor to world power generation with applications ranging from electricity production to aircrafts propulsion. Their efficiency is subject to continuous research. A gas turbine's overall efficiency is directly proportional to flow inlet temperature. Various methods are implemented to protect hot gas path components from mainstream flow well above their melting temperature, namely, heat resistant coatings, internal cooling and film cooling. The latter is the subject of this work. A 3-D Computational Fluid Dynamics (CFD) model is solved using ANSYS CFX software and compared to experimental measurements of film cooled transonic vane cascade operating at a Mach number of 0.89; the experimental data used for validation is provided by Heat and Power Technology Department of the Royal Institute of Technology (Kungliga Tekniska Hogskolan, KTH) of Stockholm, Sweden. A new approach was used to model the film cooling holes, omitting the need to model both the coolant plenum and cooling tubes, resulting in 180% reduction in grid size and attributed computational cost interpreted in 300% saving in computation time. The new approach was validated on a basic flow problem (flat plate film cooling) and was found to give good agreement with experimental measurements of velocity and temperature at a blowing ratio (BR) of 1 and 2; the experimental data for the flat plate was provided by NASA's Glenn Research Center. The numerical simulation of the cooled vane cascade was compared to experimental measurements for different cooling configurations and different BRs. a) One row on pressure side at BR = 0.8, 0.96 and 2.5. b) Two rows on suction side (location 1) at BR = 0.8, 1.4 and 2.5. c) Two rows on suction side (location 2) at BR = 0.8. And d) Showerhead cooled vane at BR ranges between 1.98 and 5.84. The coolant was applied at the same temperature as the mainstream, to match experimental conditions. A good agreement with the experimental measurements was obtained for exit flow angle, vorticity downstream of the vane, pressure coefficients and aerodynamic loss. The proposed approach of coolant injection modeling is shown to yield reliable results, within the uncertainty of the measurements in most cases. Along with lower computational cost compared to conventional film cooling modeling approach, the new approach is recommended for further analysis for aero and thermal vane cascade flows.
Author: Manasa Sahini Publisher: ISBN: Category : Data libraries Languages : en Pages : 111
Book Description
Data centers house a variety of compute, storage, network IT hardware where equipment reliability is of utmost importance. Heat generated by the IT equipment can substantially reduce its service life if Tj,max, maximum temperature that the microelectronic device tolerates to guarantee reliable operation, is exceeded. Hence, data center rooms are bound to maintain continuous conditioning of the cooling medium. This approach often results in over-provisioned cooling systems. In 2014, U.S. Data center electricity consumption is about 1.8% of the total electrical energy in the country. Hence, data center power and cooling have become significant issues facing the IT industry. The first part of the study focuses on air cooling of electronic equipment at room level. Data centers are predominantly cooled by perimeter computer air handling units that supply cold air to the raised floor plenum and the cold air helps in removing the heat generated by IT equipment. This method tends to be inadequate especially when the average power density per rack rises above 4 kW. As a solution to mitigate this problem, different rack and row based cooling solutions have been proposed and used. The primary focus of these cooling methods is to bring cooling closer to the heat source which is the IT rack thereby improving the heat dissipation process along with controlled air flow management in the data center room. Mostly known close-coupled cooling solutions include rear-door heat exchanger, in-row coolers, and over-head cooling. In this study, a new end-of-aisle close-coupled cooling solution for small data center cooling room has been proposed. As oppose to the existing designs, this design is distinctive in eliminating the risk of placing the liquid on top of IT racks along with achieving cooling energy efficiency. Three different configurations of the proposed designs are studied for its thermal performance using computational modeling. The second part of the study focuses on liquid cooling at rack level. Liquid cooling addresses the critical issues related to typical air cooling in servers because of its better heat transfer characteristics. Water-cooling at the device level can be an efficient solution since water has higher thermal capacitance when compared to traditional heat carrying medium i.e., air. The emerging practice in the data center industry is to maximize the use of economizer usage by reducing/eliminating the usage of chiller while taking advantage of outside ambient conditions to cool the data centers. Liquid cooled racks are generally designed with different configuration of pumping systems. Empirical study is conducted on a state-of-art liquid cooled electronic rack for high coolant inlet, commonly known as warm-water cooling in order to evaluate the cooling performance of distributed vs. centralized coolant pumping systems. Experimental set up is instrumented such that detailed analysis is employed to study component temperatures as well as cooling performance of the rack at elevated inlet conditions. The third part of the study focuses on the impact of high server inlet temperatures to static power at server level. In order to maximize the use of economizers, the IT hardware will be exposed to higher inlet temperatures which would lead to higher operating temperatures of the processors. The operating temperature of the CPU has direct influence on the static power due to subthreshold leakage which is known to reduce the performance of the processor. The current work serves as a firsthand investigation to study trade-off between IT performance and energy efficiency for elevated inlet temperature in air vs. liquid cooled servers. Air cooled IT along with the liquid cooled counter-parts are instrumented and extensively tested to simulate the high ambient conditions at the test bed data center.
Author: Gerard Scheepers Publisher: ISBN: Category : Languages : en Pages :
Book Description
Developments regarding internal cooling techniques have allowed the operation of modern gas turbine engines at turbine inlet temperatures which exceed the metallurgical capability of the turbine blade. This has allowed the operation of engines at a higher thermal efficiency and lower specific fuel consumption. Modern turbine blade-cooling techniques rely on external film cooling to protect the outer surface of the blade from the hot gas path and internal cooling to remove thermal energy from the blade. Optimization of coolant performance and blade-life estimation require knowledge regarding the influence of cooling application on the blade inner and outer surface heat transfer. The following study describes a combined experimental and computational study of heat transfer augmentation near the entrance to a film-cooling hole. Steady-state heat transfer results were acquired by using a transient measurement technique in an 80 x actual rectangular channel, representing an internal cooling channel of a turbine blade. Platinum thin-film gauges were used to measure the inner surface heat transfer augmentation as a result of thermal boundary layer renewal and impingement near the entrance of a film-cooling hole. Measurements were taken at various suction ratios, extraction angles and wall temperature ratios with a main duct Reynolds number of 25? 103. A numerical technique, based on the resolution of the unsteady conduction equation, using a Crank-Nicholson scheme, was used to obtain the surface heat flux from the measured surface temperature history. Computational data was generated with the use of a commercial CFD solver.
Author: Daniel Gutierrez (M.S. in Engineering) Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Advancement in additive manufacturing (AM) methods along with the application to gas turbine component manufacturing has expanded the feasibility of creating complex hole geometries to be used in gas turbines. The design possibilities for new hole geometries have become unlimited as these improved AM methods allow for the creation of holes with complex hole geometries such as rounded inlets, protrusions in the surface of the inlet and outlet of holes, among others. This advancement in such technology has sparked interest among turbine research groups for the design and creation of optimized versions of holes that showcase sophisticated geometries, which would otherwise not be possible to be manufactured using conventional manufacturing methods. Recently, a computational adjoint based optimization method by a past student in our lab (Fraser B. Jones) was used to design shaped film cooling holes fed by internal co-flow and cross-flow channels. The CFD simulations for said hole geometries predicted that the holes optimized for use with cross-flow (X-AOpt) and co-flow (Co-AOpt) would significantly increase adiabatic effectiveness. However, only the X-AOpt hole was tested experimentally in this previous study. In this study, adiabatic and matched Biot number models were built for 5X engine scale models of the X-AOpt and Co-AOpt shaped holes and tested experimentally in a low speed wind tunnel facility. The optimized shaped holes are experimentally evaluated using measurements of adiabatic effectiveness and overall cooling effectiveness. Coolant was fed to the holes with an internal co-flow channel and tested at various blowing ratios (M=0.5-4). For reference, experiments were also conducted with 5X engine scale models for the baseline 7-7-7 sharp inlet (SI) shaped hole, and a 15-15-1 rounded inlet (RI) shaped hole (shown in a previous parametric optimization study by Jones to be the optimum expansion angles for a shaped hole). Discharge coefficient, C [subscript d], measurements for the Co-AOpt geometry are analyzed in greater detail and compared against the other hole geometries tested for the study. In addition, computational predictions of C [subscript d] for a 15-15-1 RI hole will be compared against experimental measurements from this study. Results from the experiments performed at the low speed facility for 5X scale models confirmed that the X-AOpt hole had a 75% increase in adiabatic effectiveness compared to the 7-7-7 SI shaped hole. However, the Co-AOpt hole had only a 30% increase in adiabatic effectiveness, which is substantially less than had been computationally predicted
Author: Sangkwon Na Publisher: ISBN: Category : Languages : en Pages : 382
Book Description
Advanced gas turbines are designed to operate at increasingly higher inlet temperatures to increase efficiency and specific power output. This increase in the operating temperature is enabled by advances in high-temperature resistant materials such as super alloys and thermal-barrier coatings (TBCs) and by the development of effective cooling methods that lower the temperature of all surfaces that come in contact with the hot gases. Since the lower-temperature air used for cooling is extracted from the compressor, efficiency considerations demand effective cooling with minimum cooling flow. This study focuses on film cooling with a twofold objective. The first is to examine the effects of TBC blockage and surface roughness on film-cooling effectiveness. The second objective is to explore, develop, and evaluate more efficient film-cooling methods. This study is accomplished by using second-order accurate computational fluid dynamics (CFD) analyses of the "compressible" Navier-Stokes equations in which the details of the film-cooling geometry and relevant flow features are resolved. To ensure that the solutions generated are meaningful, a grid-sensitivity study was performed for each configuration examined. Also, a validation study was performed to assess the turbulence models used.
Author: Katharine Lee Harrison
Author: Katharine Lee Harrison
Author: 
Author: Thomas Earl Dyson
Author: Ahmad Mahmoud Alameldin
Author: Pradeep S. Kamath
Author: Manasa Sahini
Author: Gerard Scheepers
Author: Daniel Gutierrez (M.S. in Engineering)
Author: Sangkwon Na
Author: D. Giebert