Khalid Parvez

Transition Prediction in Low Pressure Turbine (LPT) Using Gamma Theta Model and Passive Control of Separation

The boundary layer of low-pressure turbine blades has received a great deal of attention due to advent of high lift and ultra high lift LP turbines. At cruising condition, Reynolds number is very low in engine and LP turbine performance suffers mainly from losses due to the laminar separation bubble on suction surface. In this paper, T106A low pressure turbine profile has been used to study the behavior of boundary layer and subsequently, flow is controlled using the passive technique. Unsteady Reynolds Averaged Navier Stokes equations were solved using SST Gamma-Theta transition model for turbulence closure. Hybrid mesh topology has been used to discretize the computational domain, with highly resolved structured mesh in boundary layer (Y+ < 1) and unstructured mesh in the rest of domain. Simulations were performed using commercial CFD code ANSYS FLUENT ® at Reynolds number 91000 (based on inlet velocity and chord length) and turbulence intensity of 0.4%. To study the effect of dimple on the flow separation, dimple has been positioned at different axial location on the suction side. It was found that shifting the dimple downstream results in controlled flow and reduced loss coefficient as compared to the case when no dimple is applied.Copyright

Flow controlling on low pressure turbine using passive methods

Flow control in low pressure turbine using passive devices is efficient technique to raise the efficiency of engine. In this study T106A LP Turbine geometry is used for controlling the flow separation using passive device. A lot of work is done for flow controlling using different kind of passive devices like dimples, bumps, riblets etc. Work on the backward step geometry for controlling the flow separation is not done effectively. Fine structured mesh is created with boundary layer (y + <; 1) an unstructured meshing in the rest of the domain. Unsteady RANS are solved using the Gamma-Theta Model Transitional Model for capturing the laminar separation bubble. In this study a smooth backward step of different height to length ratios (h/1) are applied on the 65% axial chord length for the reduction of loss coefficient which is another way to specify the efficiency of turbine using pressure values. After specifying the best h/1 ratio at 65% axial chord where the losses are minimum, this specific h/1 ratio step is shifted at different axial locations to And out the optimal location where the maximum losses are reduced. By making the coefficient of pressure plots and boundary layer profiles, it has been confirmed that backward step completely control the laminar separation bubble and also reduce the loss coefficient.

Effect of turbulence intensities and passive flow control on LP turbine

Flow controlling of boundary layers separation of low-pressure (LP) turbine blade is still a high leverage area for advent of high lift and ultra-high lift LP turbines. At cruising conditions, the Reynolds number in the LP turbine reduces (due to the decrease in air density) to the critical value that flow starts to separate from the blade suction surface. In the present study, cascade T106A is used to control the laminar separation bubble on the suction side of the blade. Fluent® commercial CFD code with gamma theta transition model has been employed to study the boundary layer separation at various different turbulent intensities. Numerical results are validated with the available experimental data and are in good agreement. An optimize dimple is used to control the boundary layer separation at low and intermediate turbulent intensities. Normalized loss coefficient is reduced to about 5% with the help of optimal dimple size and location, which increase the LP turbine efficiency. Cp plots and boundary layers profiles are made for flow visualization.

Element-Free Galerkin Method Based on Block-Pulse Wavelets Integration for Solving Fourth-Order Obstacle Problem

We introduce improved element-free Galerkin method based on block pulse wavelet integration for numerical approximations to the solution of a system of fourth-order boundary-value problems associated with obstacle, unilateral, and contact problems. Moving least squares (MLS) approach is used to construct shape functions with optimized weight functions and basis. Numerical results for test problems are presented in this article to elaborate the pertinent features for the proposed technique. Comparison with existing techniques shows that our proposed method based on integration technique provides better approximation at reduced computational cost.

Simulation of First Mode Crack Propagation in a Viscoelastic Solid System Fuel Structure Using Crack Length-Temperature Superimposition

Fractures in Solid system fuel structure pose a huge risk to structural integrity of the system. Ansys APDL scripting language has been used to analyze fractures with different geometry, material and loading. Parameterization of simulations resulted in developing a tool for solid fuel system designers to perform a quick fracture analysis during their design iterations. Numerical simulation results have been compared with the experimental data and a good agreement between the two has been found, ascertaining our numerical approach for the assessment of the problem. Crack length-Temperature superimposition has been performed to obtain master curves for the data, which can be used to predict stress intensity factor at different crack lengths.

Study of Flow Controlling on LP Turbine at Different Reynolds Number

Active and passive techniques have been used in the past, to control flow separation. Numerous studies were published on controlling and delaying the flow separation on low pressure turbine. In this study, a single dimple (i.e. passive device) is engraved on the suction side of LP turbine cascade T106A. The main aim of this research is to find out the optimum parameters of dimple i.e. diameter (D) and depth (h) which can produce strong enough vortex that can control the flow either in transition or fully turbulent phase. Furthermore, this optimal dimple is engraved to suppress the boundary layer separation at different Reynolds number (based on the chord length and inlet velocity). The dimple of different depth and diameter are used to find the optimal depth to diameter ratio. Computational results show that the optimal ratio of depth to diameter (h/D) for dimple is 0.0845 and depth to grid boundary layer (h/δ) is 0.5152. This optimized dimple efficiently reduces the normalized loss coefficient and it is found that the negative values of shear stresses found in uncontrolled case are being removed by the dimple. After that, dimple of optimized parameters are used to suppress the laminar separation bubble at different Re∼25000, 50000 and 91000. It was noticed that the dimple did not reduce the losses at Re∼25000. But at Re∼50000, it produced such a strong vortex that reduced the normalized loss coefficient to 25%, while 5% losses were reduced at Re∼91000. It can be concluded that the optimized dimple effectively controlled flow separation and reduced normalized loss coefficient from Re 25000 to 91000. As the losses are decreased, this will increase the low pressure turbine efficiency and reduce its fuel consumption.© 2012 ASME

Novel Aerodynamic Compensation Pitot - Static Tube for Application in Subsonic and Supersonic Flight Regimes

An aerodynamic compensation pitot -static tube has been developed for the flight regime of modern fighter aircraft ( Mach < 2). The pitot -static tube profile has been designed so th at in the subsonic regime it aerodynamically compensates for the position error in pressure coefficient (Cp) due to presence of the aircraft, while in the supersonic regime it gives the desired zero compensation. The unique aspect of the new design is that it is able to provide the desired compensation in both subsonic (negative Cp) and supersonic (zero Cp) re gimes at same axial location. At this axial location the local Cp gradient is small in the subsonic regime and is close to zero in the supersonic regi me so that in practical application this pitot static tube would be less sensitive to manufacturing tolerances. The new design pitot -tube can be used effectively to compensate for Cp position errors of up to + 0. 1 in the subsonic regime by non -dimensional “ stretching” of the basic profile while maintaining zero Cp in the supersonic regime. Computational Fluid Dynamics tools have been used in the design and analysis of the new pitot -static tub e. The effect of turbulence model and grid size on compute d results has been evaluated. The complete Mach number regime (Mach < 2) has been computationally explored for different profiles resulting for m “stretching” of the basic profile in order to validate the new design’s capability to compensate position errors in Cp o f up to + 0. 1. In the end a design methodology is also presented where a specific pitot -static tube profile can be extracted from the general non -dimensional profile in order to aerodynamically compensate a known position error in Cp.