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Author: Daniel R. Rogers Publisher: 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.
Author: Daniel R. Rogers Publisher: 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.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Low-pressure turbines (LPT) experience large changes in chord Reynolds number as the turbine engine operates from take-off to cruise conditions. Due to prevailing conditions at high altitude cruise, the Reynolds number reduces drastically. At low Reynolds numbers, the flow is largely laminar and tends to separate easily on the suction surface of the blade, and this laminar separation in particular leads to significant degradation of engine performance due to large re-circulation zones. Therefore, a better understanding of low-Reynolds number flow transition and separation is very critical for an effective design of LPT blade, and in exploring various possibilities for implementing flow control techniques, passive or active, to prevent or delay the flow separation in the low-pressure turbine. The objective of the present study is to understand the three-dimensional flow separation that occurs inside an LPT cascade at very low Reynolds numbers, and a high-order accurate numerical solution procedure is used to attain the same. A multi-block, periodic, structured grid generated by the grid generation software, GRIDPRO, is used to represent the flow domain. A MPI-based higher-order, parallel, chimera version of the FDL3DI flow solver, developed by the Air Force Research Laboratory at Wright Patterson Air Force Base, is extended for the present turbomachinery application. A sixth-order accurate compact-difference scheme is used for the spatial discretization, along with second-order accurate temporal discretization. Up to tenth-order filtering has been applied to minimize the numerical oscillations, and maintain numerical stability. Simulations have been performed for Reynolds numbers (based on inlet velocity and axial chord) 10,000 and 25,000. The effect of these low-Reynolds numbers on the flow physics for a low-pressure turbine cascade has been studied in detail. At Re = 10,000, the flow undergoes more separation than at Re = 25,000 as expected and the separation remains significant over the entire blade for both the Reynolds number. The location of the onset of separation matches with an available LES simulation and with the available experimental data. In addition to the above simulations, another study was carried out to understand the effect of two different sets of inflow/outflow boundary conditions on the flow solution. The two sets of boundary conditions include static inflow with extrapolated outflow (BC1), and dynamic inflow (BC2) that accounts for upstream influence in the subsonic flow. The computed Cp distribution for the LPT flow shows good agreement with the available experimental data. Application of BC2 boundary condition predicted a bounded region of separation, while BC1 boundary condition predicted significant separation over the entire blade of an LPT.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Low-pressure turbines (LPT) in aircraft engines undergo tremendous losses at cruise conditions. The flow Reynolds number at cruise is lower than the take-off Reynolds number by a factor of almost two. At low Reynolds numbers, the flow is largely laminar, and tends to separate easily on the suction surface of the turbine blade when an adverse pressure gradient is encountered. Therefore, accurate prediction of flow separation is crucial for an effective design of LPT blade; and is achieved in the present work using a high-order accurate numerical solution procedure. The three-dimensional, unsteady, full Navier-Stokes equations are solved to analyze the flow. A MPI-based higher-order, parallel, chimera version of the FDL3DI flow solver, is extended for use with this turbomachinery application. A sixth-order accurate compact-difference scheme is used for the spatial discretization, along with second-order accurate temporal discretization. Tenth-order filtering is used to minimize the numerical oscillations in the flow solution and maintain numerical stability. The objective of the present study is to show the ability of higher-order accurate compact-difference scheme to predict the flow separation that occurs inside an LPT cascade at Re C = 25,000 (based on axial chord and inlet velocity). A new set of subsonic inflow/outflow boundary conditions that account for upstream influence (BC2) are derived by specifying stagnation quantities at the inlet, and a static quantity at the exit of the flow domain, and maintaining the inflow angle constant. For inflow/outflow boundary conditions that do not account for upstream influence, fixed inflow with extrapolated outflow (BC1) has been utilized. The effect of the two different sets of inflow/outflow boundary conditions on the flow solution is studied, for second-order, fourth-order and sixth-order accurate schemes. The computed Cp distribution for the LPT flow shows good agreement with the existing experimental data. The location of the onset of separation matches with an available LES simulation result and with the available experimental data. The performance of high-order compact difference schemes has been assessed via simulation of laminar flow over a circular cylinder at Re D = 250 (based on free-stream velocity and cylinder diameter). The sixth-order accurate compact difference scheme with tenth-order filtering on a coarser mesh preserves the vortex structure better than possible with the second-order accurate scheme on a finer mesh. This demonstrates the efficiency of the higher-order accurate compact difference scheme.
Author: Ashlie B. Flegel Publisher: ISBN: Category : Cascades (Fluid dynamics) Languages : en Pages : 56
Book Description
Abstract: The purpose of this thesis is to document the impact of incidence angle and Reynolds number variations on the 3-D flow field and midspan loss and turning of a 2-D section of a variable-speed power-turbine (VSPT) rotor blade. Aerodynamic measurements were obtained in a transonic linear cascade at NASA Glenn Research Center in Cleveland, OH. Steady-state data were obtained for ten incidence angles ranging from +15.8° to -51.0°. At each angle, data were acquired at five flow conditions with the exit Reynolds number (based on axial chord) varying over an order-of-magnitude from 2.12 × 105 to 2.12 × 106. Data were obtained at the design exit Mach number of 0.72 and at a reduced exit Mach number of 0.35 as required to achieve the lowest Reynolds number. Midspan total-pressure and exit flow angle data were acquired using a five-hole pitch/yaw probe surveyed on a plane located 7.0 percent axial-chord downstream of the blade trailing edge plane. The survey spanned three blade passages. Additionally, three-dimensional half-span flow fields were examined with additional probe survey data acquired at 26 span locations for two key incidence angles of +5.8° and -36.7°. Survey data near the endwall were acquired with a three-hole boundary-layer probe. The data were integrated to determine average exit total-pressure and flow angle as functions of incidence and flow conditions. The data set also includes blade static pressures measured on four spanwise planes and endwall static pressures.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The Reynolds number for the flow through LPT at cruise conditions is much lower than that at the take-off conditions. This low-Re flow has a great tendency to undergo separation on the suction surface of the turbine blade when an adverse pressure gradient is encountered. This prevailing flow separation is detrimental to the performance of the LPT. Hence, low-pressure turbine (LPT) stage in aircraft engines undergo significant losses during cruise conditions. Therefore, accurate prediction of flow separation is crucial for an effective design of LPT blade, and is achieved in the present work using a high-order accurate numerical solution procedure. The accurate prediction of flow separation is necessary for implementing flow control techniques, passive or active, to possibly delay or prevent the occurrence of flow separation in the low-pressure turbine stage in an aircraft engine. A multi-block, periodic, structured grid of multiple topologies generated by the grid generation software, GRIDPRO, is used for the present numerical analysis. The three-dimensional, unsteady, full Navier-Stokes equations are solved to analyze the flow. A MPI-based higher-order, parallel, chimera Large-Eddy Simulation (LES), version of the FDL3DI flow solver, developed by the Air Force Research Laboratory at Wright Patterson Air Force Base, is extended for the present turbo-machinery application. A sixth-order accurate compact-difference scheme is usual for the spatial discretization, coupled with tenth-order filtering to minimize the numerical oscillations in the flow solution and maintain numerical stability, along with second-order accurate temporal discretization. Also examined is the effect of grid density and the location of the upstream inflow boundary ... Finally, the baseline simulation study of flow over a circular cylinder at ReD = 13,400 is performed as a starting step for the future study of implementation of flow control techniques for preventing or delaying the flow separation.
Author: S. Kishore Kumar Publisher: Springer Nature ISBN: 9811596018 Category : Technology & Engineering Languages : en Pages : 529
Book Description
This book presents selected papers presented in the Symposium on Applied Aerodynamics and Design of Aerospace Vehicles (SAROD 2018), which was jointly organized by Aeronautical Development Agency (the nodal agency for the design and development of combat aircraft in India), Gas-Turbine Research Establishment (responsible for design and development of gas turbine engines for military applications), and CSIR-National Aerospace Laboratories (involved in major aerospace programs in the country such as SARAS program, LCA, Space Launch Vehicles, Missiles and UAVs). It brings together experiences of aerodynamicists in India as well as abroad in Aerospace Vehicle Design, Gas Turbine Engines, Missiles and related areas. It is a useful volume for researchers, professionals and students interested in diversified areas of aerospace engineering.
Author: Burak Ozturk Publisher: ISBN: Category : Languages : en Pages :
Book Description
Detailed experimental investigation has been conducted to provide a detailed insight into the heat transfer and aerodynamic behavior of a separation zone that is generated as a result of boundary layer development along the suction surface of a highly loaded low pressure turbine (LPT) blade. The research experimentally investigates the individual and combined effects of periodic unsteady wake flows and freestream turbulence intensity (Tu) on heat transfer and aerodynamic behavior of the separation zone. Heat transfer experiments were carried out at Reynolds number of 110,000, 150,000, and 250,00 based on the suction surface length and the cascade exit velocity. Aerodynamic experiments were performed at Re = 110,000 and 150,000. For the above Re-numbers, the experimental matrix includes Tus of 1.9%, 3.0%, 8.0%,13.0% and three different unsteady wake frequencies with the steady inlet flow as the reference configuration. Detailed heat transfer and boundary layer measurements are performed with particular attention paid to the heat transfer and aerodynamic behavior of the separation zone at different Tus at steady and periodic unsteady flow conditions. The objectives of the research are (a) to quantify the effect of Tu on the aero-thermal behavior of the separation bubble at steady inlet flow condition, (b) to investigate the combined effects of Tu and the unsteady wake flow on the aero-thermal behavior of the separation bubble, and (c) to provide a complete set of heat transfer and aerodynamic data for numerical simulation that incorporates Navier-Stokes and energy equations. The analysis of the experimental data reveals details of boundary layer separation dynamics which is essential for understanding the physics of the separation phenomenon under periodic unsteady wake flow and different Reynolds number and Tu. To provide a complete picture of the transition process and separation dynamics, extensive intermittency analysis was conducted. Ensemble averaged maximum and minimum intermittency functions were determined leading to the relative intermittency function. In addition, the detailed intermittency analysis reveals that the relative intermittency factor follows a Gaussian distribution confirming the universal character of the relative intermittency function.
Author: Daniel R. Rogers
Author: Daniel R. Rogers
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Author: Robert E. Forrette
Author: Robert H. Davis
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Author: Ashlie B. Flegel
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Author: 
Author: S. Kishore Kumar
Author: Burak Ozturk