Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 32
Book Description
Progress in Modeling of Laminar to Turbulent Transition on Turbine Vanes and Blades
Author: Two-equation Low-Reynolds-number Turbulence Modeling of Transitional Boundary Layer Flows Characteristic of Gas Turbine Blades
Author: Rodney C. SchmidtNumerical Simulation of Turbine Blade Heat Transfer Using Two-equation Turbulence Models
Author: Abdul Hafid M. ElfaghiPublisher:
ISBN:
Category : Turbines
Languages : en
Pages : 216
Book Description
The development of high performance gas turbines requires high turbine inlet temperatures that can lead to severe thermal stresses in the turbine blades, particularly in the first stages of the turbine. Therefore, the major objective of gas- turbine designers is to determine the thermal and aero-dynamical characteristics of the turbulent flow in the turbine cascade. This work is a numerical simulation of fluid flow and heat transfer in the turbine blade using different two-equation turbulence models. The turbulence models used here were based on the eddy viscosity concept, which determined the turbulent viscosity through time-averaged Navier-Stokes differential equations. The most widely accepted turbulence models are the two-equation models, which involves the solution of two transport equations for the turbulent kinetic energy, k, and its rate of dissipation, & or In the present simulation, four two-equation turbulence models were used, the standard k-& model, the modified Chen-Kim k-& model, RNG model and Wilcox standard k - OJ turbulence model. A comparison between the turbulence models and their predictions of the heat flux on the blade were carried out. The results were also compared with the available experimental results obtained from a research carried out by Arts et at. (1990) at the von Karman Institute of Fluid Dynamics (VKI). The simulation was performed using the general-purpose computational fluid dynamics code, PHOENICS, which solved the governing fluid flow and heat transfer equations. An H-type, body-fitted-co-ordinate (BFC) grid was used and upstream and downstream periodic conditions were specified. The grid system used was, sufficiently fine and the results were grid independent. All models demonstrated good heat transfer predictions for the pressure side except close to the leading edge. On the suction side, standard model over-predicted the heat transfer, whereas Chen-Kim, RNG and k - OJ models captured the overall behaviour quite well. Unlike k - OJ model, all k - & models generated very high turbulence levels in the stagnation point regions, which gave rise to the heat transfer rates close to the leading edge.
Study of Boundary Layer Development in a Two-Stage Low-Pressure Turbine
Author: National Aeronautics and Space Adm NasaPublisher: Independently Published
ISBN: 9781723760280
Category : Science
Languages : en
Pages : 30
Book Description
Experimental data from jet-engine tests have indicated that unsteady blade row interactions and separation can have a significant impact on the efficiency of low-pressure turbine stages. Measured turbine efficiencies at takeoff can be as much as two points higher than those at cruise conditions. Several recent studies have revealed that Reynolds number effects may contribute to the lower efficiencies at cruise conditions. In the current study numerical simulations have been performed to study the boundary layer development in a two-stage low-pressure turbine, and to evaluate the transition models available for low Reynolds number flows in turbomachinery. The results of the simulations have been compared with experimental data, including airfoil loadings and integral boundary layer quantities. The predicted unsteady results display similar trends to the experimental data, but significantly overestimate the amplitude of the unsteadiness. The time-averaged results show close agreement with the experimental data.Dorney, Daniel J. and Ashpis, David E. and Halstead, David E. and Wisler, David C.Glenn Research CenterJET ENGINES; TWO STAGE TURBINES; COMPUTERIZED SIMULATION; BALDWIN-LOMAX TURBULENCE MODEL; BOUNDARY LAYER TRANSITION; TRANSITION FLOW; FLOW VISUALIZATION; BOUNDARY LAYER SEPARATION; SEPARATED FLOW; ROTOR BLADES (TURBOMACHINERY); TAKEOFF; CRUISING FLIGHT; COMPUTATIONAL GRIDS; NOZZLE FLOW; SKIN FRICTION; TURBINE BLADES; REYNOLDS NUMBER; FLOW CHARACTERISTICS; FLOW DISTRIBUTION
Modelling of Laminar-turbulent Transition for High Freestream Turbulence
Author: J. SteelantTurbulent Spot Characterization and the Modeling of Transitional Heat Transfer in Turbines
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
Optimum design of gas turbine blades depends on accurate prediction of boundary layer transition. The purpose of this research is to obtain more information on the generation. propagation and coalescence of turbulent spots in a transitional boundary layer and examine the effects of free stream turbulence pressure gradient and cross flow. Experimental data from this study may be used to improve existing CFD models, allowing designers to make more accurate predictions of transitional heat transfer in turbines.
Design of a Three-passage, Low Reynolds Number Turbine Cascade with Periodic Flow Conditions
Author: Daniel R. RogersPublisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 116
Book Description
A numerical method for modeling a low Reynolds number turbine blade, the L1M, is presented along with the pitfalls encountered. A laminar solution was confirmed to not accurately predict the flow features known in low Reynolds number turbine blade flow. Three fully turbulent models were then used to try to predict the separation and reattachment of the flow. These models were also found to be insufficient for transitioning flows. A domain was created to manually trip the laminar flow to turbulent flow using a predictive turbulence transition model. The trip in the domain introduced an instability in the flow field that appears to be dependent on the discretization order, turbulence model, and transition location. The method was repeated using the Pack B blade and the same obstacles were apparent. The numerical method developed was then used in an optimization technique developed to design a wind tunnel simulating periodic flow conditions using only 2 blades. The method was first used to predict a cp distribution for the aft loaded L1A research blade provided by the U.S. Air Force. The method was then extended to a larger domain emulating the 2 blade, 2D wind tunnel. The end-wall geometry of the tunnel was then changed using previously defined control points to alter the distribution of cp along the suction surface of the interior blades. The tunnel cp's were compared to the computationally acquired periodic solution. The processed was repeated until an acceptable threshold was reached. The optimization was performed using the commercially available software iSIGHT by Engineous Solutions. The optimization algorithms used were the gradient based Successive Approximation Method, the Hooke Jeeves, and Simulated Annealing.
Visualization of Transition Phenomena in the Boundary Layer on the Blades of a Turbine Cascade
Author: A. Ya IpatenkoPublisher:
ISBN:
Category :
Languages : en
Pages : 10
Book Description
In investigating the flow in the boundary layer on the blades of a cascade to determine the line of transition from laminar flow to turbulent flow and to establish the boundaries of the effect of the face walls of the channel, the kaolin and the sublimation methods can be successively applied. Both methods are approximately equivalent. The kaolin method is somewhat more convenient and gives a clearer boundary between the regions. (Author).
Author: Özge Sinem Özçakmak
Author: Boris A. Bangert