• M SIVAPRAGASAM

      Articles written in Sadhana

    • Effect of leading-edge geometry on the aerodynamics and heat transfer in the stagnation region of uncooled turbine blades

      A AROCKIA FENIL M SIVAPRAGASAM

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      The flow in the leading-edge stagnation region of uncooled turbine aerofoils is studied. The stagnation region is modelled based on the Hiemenz flow solution, following Holley and Langston (J. Turbomach. 130: 021001, 2008). These results are applied to the JT9D turbine blade and confirmed by computations. It is also shown that the heat transfer at the stagnation point is bounded by the Hiemenz flow and plane stagnation-point potential flow heat transfer solutions. The computations are further extended for a range of Reynolds numbers and freestream turbulence intensities. It is seen that for a wide range of these parameters considered in the present study and data collected from published literature, a majority of the data points are within these bounds. The leading-edge geometry of the JT9D turbine blade is modified with elliptical geometries.Blunter-leading-edge geometries have lower values of heat transfer at the stagnation region; however, their blade profile loss coefficients are higher. The off-design performance characteristics of the turbine blades are also computed. The results presented in this paper will be useful in designing leading-edge geometries for reduced heat transfer in the stagnation region of uncooled turbine blades.

    • Negative lift characteristics of NACA 0012 aerofoil at low Reynolds numbers

      C PRANESH M SIVAPRAGASAM M D DESHPANDE H K NARAHARI

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      Numerical investigations on the flow over NACA 0012 aerofoil are carried out to provide better understanding of the unusual lift characteristics exhibited by this aerofoil at low Reynolds numbers. Computations are carried out at Re = 10,000–100,000, for different values of angles of attack and freestream turbulenceintensity. There exists a narrow range of these parameters where the net circulation around this symmetrical aerofoil is negative, leading to the generation of negative lift at positive angles of attack. Different flow regimes are identified and physical explanations are given for this unusual behaviour of negative lift, andthe influence of different flow parameters is discussed.

    • Aerodynamic shape optimization of airfoils at ultra-low Reynolds numbers

      MEEDHU GEOGY UKKEN M SIVAPRAGASAM

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      The flow over NACA 0008 airfoil is studied computationally in the ultra-low Reynolds number regime Re ∈ [1000, 10000] for various angles of attack α ∈ [0°, 8°]. The laminar flow separation occurs even atlow angles of attack in this Reynolds number regime. The lift curve slope is far reduced from the inviscid thin airfoil theory value of Clα = 2π Significant increase in the values of drag coefficient is seen with a decrease in Re. Lift-to-drag ratios are consequently very low. An adjoint-based aerodynamic shape optimization methodology is employed to obtain improved aerodynamic characteristics in the ultra-low Re regime. Three differentobjective functions are considered, namely, (i) minimization of drag coefficient, Cd, (ii) maximization of lift coefficient, Cl, and (iii) maximization of lift-to-drag ratio, (Cl/Cd). Significant improvement in each of the objective functions is obtained.

    • An efficient miniature air suction system for chemical sensors for micro air vehicle application

      M D DESHPANDE M SIVAPRAGASAM S UMESH

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      This paper describes the design of a miniature air suction system to house a chemical sensor. It has been designed to improve the aerodynamic chemical sensing efficiency and to have a low weight since it is meant to be mounted on a micro air vehicle. The design is done around a readily available miniature axial flow fan by computational methods. A converging-diverging shape for the air suction system with the sensor disc having a central hole and mounted at the throat is proposed as good design concept. The systematic approach hasled to a light weight system with high aerodynamic efficiency even under extreme flow conditions that may be caused by MAV manoeuvre or cross winds.

    • Multi-fidelity surrogate model-based airfoil optimization at a transitional low Reynolds number

      R PRIYANKA M SIVAPRAGASAM

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      The aerodynamic design optimization of an airfoil is carried out at a transitional low Reynolds number in the framework of multi-fidelity surrogate modeling. Two multi-fidelity surrogate-based optimization methodologies are proposed. The first method involves the co-Kriging surrogate model with prediction-basedhigh-fidelity model update strategy. The second method uses the Kriging model of the low-fidelity function, and subsequent co-Kriging modeling with high-fidelity infills done using the gradient-free trust-region approach. The high-fidelity solutions are obtained by solving the Reynolds-averaged Navier-Stokes equations with the flow transition modeled by the γ-Reθ model. The low-fidelity solutions are obtained by a panel code in conjunction with the eN method. The proposed optimization methodologies are applied to two different objective functions in the transitional low Reynolds number regime, namely, (i) maximization of lift coefficient, and (ii) maximization of endurance factor. Significant improvements in each of the objective functions are obtained using both thesemethodologies.

    • Multi-objective design optimization of turbine blade leading edge for enhanced aerothermal performance

      M TEJASWINI M SIVAPRAGASAM

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      A multi-objective design optimization is carried out to minimize the heat transfer in the leading edge region of an uncooled turbine blade and the blade profile loss. These objectives pose conflicting requirements. The leading edge of Pratt and Whitney JT9D turbine blade is parameterized by Béizer curves. TheLatin hypercube sampling plan is used to sample the design space. Several turbine blade geometries are created and their heat transfer and aerodynamic characteristics are evaluated using high-fidelity Reynolds-averaged Navier–Stokes (RANS) simulations. Kriging surrogate models are constructed using these datasets. The surrogate models are used in a genetic algorithm optimization framework to obtain optimal designs. The maximumheat transfer in the leading edge region is reduced by 5.9%. The blade profile loss is reduced by 18.1%. The surrogate models are then subject to multi-objective genetic algorithm optimization to reduce both the maximumheat transfer and the blade profile loss. A Pareto-optimal front is obtained which contains the optimal solutions. Some optimal solutions in the Pareto front are chosen and the trade-off between the competing objective functions is presented.

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