Outer Blade Surface Research Articles

Effect of Semi-elliptical Outer Blade-surface on the Savonius Hydrokinetic Turbine Performance: A Numerical Investigation

Effect of Semi-elliptical Outer Blade-surface on the Savonius Hydrokinetic Turbine Performance: A Numerical Investigation

On the electrical breakdown of GFRP wind turbine blades due to direct lightning strokes

Lightning puncture damage on the wind turbine blades can pose a severe threat to the safe operation of large-capacity wind turbines. We investigated its formation by performing long air gap discharge experiments under positive and negative downward leaders. Upward streamers were observed to emit from the sample blade before its electrical breakdown. To explain this phenomenon, a numerical model considering the streamer discharge in air, charge transport in GFRP laminate and surface charge accumulation on air-solid interfaces was established. It is found that streamer discharges can be triggered inside the blade hollow to generate space and surface charges, which strengthen the electric field on the outer blade surface and contribute to the upward streamer initiation. The upward streamer development leads to the accumulation of surface charges with opposite polarities on the two sides of GFRP laminate, which causes the electric field on the GFRP laminate to exceed its electrical breakdown threshold. The electrical breakdown, which occurs before the thermal effect of lightning current appears, is the initial stage of lightning puncture damage of blades. The electrical discharge inside the blade hollow and the surface charge accumulation on the GFRP blade should be suppressed to prevent the puncture damage of blades.

Application of conjugate heat transfer and fluid network analysis to improvement design of turbine blade with integrated cooling structures

A combination of fluid network analysis method with conjugate heat transfer are applied to the improvement design of the integrated cooling structures in a high-performance turbine blade, coupled with the 3D viscous solver for the gas flow field. By comparison with the experimental results of open literatures, the methodology developed is numerically validated. For a high-pressure turbine rotor blade, it is used to rapidly predict and evaluate the aerodynamic and heat transfer performances of its integrated inner cooling structures. According to the computation results, three ways are definitely proposed for the improvement design, including the adjustment of the coolant flow mass entering into the front and rear cavities in a more appropriate flow mass ratio, the improvement of the turning geometries in serpentine channels to minimize the inner coolant flow resistance, and the adjustment of the local cooling structure dimension according to the high temperature region on outer surface of blade. Through the verification of the fully 3D conjugate heat transfer simulation for the fields of gas flow, solid blade and coolant flow, it shows that the maximum temperature on rotor blade surface is reduced obviously, the temperature distribution becomes more uniform after improvement, and the inlet parameters of cooling cavities are matched more reasonably. It is concluded that in this paper the fluid network combined with conjugate heat transfer significantly shortens the aerodynamic and heat transfer design cycle for the turbine blade with integrated cooling structures.

Detailed Heat Transfer Measurements in a Model of an Integrally Cast Cooling Passage

Detailed measurements of the heat transfer coefficient (htc) distributions on the internal surfaces of a novel gas turbine blade cooling configuration were carried out using a transient liquid crystal technique. The cooling geometry, in which a series of racetrack passages are connected to a central plenum, provides high heat transfer coefficients in regions of the blade in good thermal contact with the outer blade surface. The Reynolds number changes along its length because of the ejection of fluid through a series of 19 transfer holes in a staggered arrangement, which are used to connect ceramic cores during the casting process. Heat transfer coefficient distributions on these holes surface are particularly important in the prediction of blade life, as are heat transfer coefficients within the hole. The results at passage inlet Reynolds numbers of 21,667, 45,596, and 69,959 are presented along with in-hole htc distributions at Rehole=5930, 12,479, 19,147; and suction ratios of 0.98, 1.31, 2.08, and 18.67, respectively. All values are engine representative. Characteristic regions of high heat transfer downstream of the transfer holes were observed with enhancement of up to 92% over the Dittus–Boelter level. Within the transfer holes, the average htc level was strongly affected by the cross-flow at the hole entrance. htc levels were low in these short (l/d=1.5) holes fed from regions of developed boundary layer.

Interaction Sites of the G Protein β Subunit with Brain G Protein-coupled Inward Rectifier K+ Channel

G protein-coupled inward rectifier K(+) channels (GIRK channels) are activated directly by the G protein betagamma subunit. The crystal structure of the G protein betagamma subunits reveals that the beta subunit consists of an N-terminal alpha helix followed by a symmetrical seven-bladed propeller structure. Each blade is made up of four antiparallel beta strands. The top surface of the propeller structure interacts with the Galpha subunit. The outer surface of the betagamma torus is largely made from outer beta strands of the propeller. We analyzed the interaction between the beta subunit and brain GIRK channels by mutating the outer surface of the betagamma torus. Mutants of the outer surface of the beta(1) subunit were generated by replacing the sequences at the outer beta strands of each blade with corresponding sequences of the yeast beta subunit, STE4. The mutant beta(1)gamma(2) subunits were expressed in and purified from Sf9 cells. They were applied to inside-out patches of cultured locus coeruleus neurons. The wild type beta(1)gamma(2) induced robust GIRK channel activity with an EC(50) of about 4 nm. Among the eight outer surface mutants tested, blade 1 and blade 2 mutants (D1 and CD2) were far less active than the wild type in stimulating GIRK channels. However, the ability of D1 and CD2 to regulate type I and type II adenylyl cyclases was not very different from that of the wild type beta(1)gamma(2). As to the activities to stimulate phospholipase Cbeta(2), D1 was more potent and CD2 was less potent than the wild type beta(1)gamma(2). Additionally we tested four beta(1) mutants in which mutated residues are located in the top Galpha/beta interacting surface. Among them, mutant W332A showed far less ability than the wild type to activate GIRK channels. These results suggest that the outer surface of blade 1 and blade 2 of the beta subunit might specifically interact with GIRK and that the beta subunit interacts with GIRK both over the outer surface and over the top Galpha interacting surface.

Investigation into Hub Effect of Marine Propeller by Surface Vortex Lattice Method

In this paper the hub effects of some model propellers are investigated by the surface vortex lattice method for the hub and by the ordinary vortex lattice method on the lifting surface for the blade. The surface, where the surface vortex lattices are distributed, is taken inside of the real surface of the hub in order to avoid the strong interference effect between the root vortex lattices of the blade and the surface vortex lattices of the hub. It is found that the hub effect is noticeable on the pressure distribution on the blade surface near the root but smaller on the outer blade surface toward the tip, but that the hydrodynamic forces of the propeller such as thrust and torque are scarcely affected by the existence of the hub of the normal size. The calculated pressure distributions on the blade including the hub effect show good or poor agreement with the measured results. The pressure distribution on the hub surface is calculated and assessed. Calculations also show that the hub effect is more significant for the larger hub diameter such as controllable pitch propellers, as expected,

Inverse Design of Composite Turbine Blade Circular Coolant Flow Passages

An inverse design and optimization method is developed to determine the proper size and location of the circular holes (coolant flow passages) in a composite turbine blade. The temperature distributions specified on the outer blade surface and on the surfaces of the inner holes can be prescribed a priori. In addition, heat flux distribution on the outer blade surface can be prescribed and iteratively enforced using optimization procedures. The prescribed heat flux distribution on the outer surface is iteratively approached by using the Sequential Unconstrained Minimization Technique (SUMT) to adjust the sizes and locations of the initially guessed circular holes. During each optimization iteration, a two-dimensional heat conduction equation is solved using direct Boundary Element Method (BEM) with linear temperature singularity distribution. For manufacturing purposes the additional constraints are enforced assuring the minimal prescribed blade wall thickness and spacing between the walls of two neighboring holes. The method is applicable to both single material (homogeneous) and coated (composite) turbine blades. Three different cases were tested to prove the feasibility and the accuracy of the method.

The Inverse Design of Internally Cooled Turbine Blades

A methodology is developed for the inverse design and/or analysis of interior coolant flow passage shapes in internally cooled configurations with particular applications to turbine cascade blade design. The user of this technique may specify the temperature (or heat flux) distribution along the blade outer fixed surface shape and the unknown interior coolant/blade interface. The numerical solution of the outer gas flow field determines the remaining unspecified blade outer surface quantity—surface heat flux if temperature was originally specified or vice versa. Along the unknown coolant flow passage shape the designer has the freedom to specify the desired temperature distribution. The hollow blade wall thickness distribution is then found from the solution of Laplace’s equation governing the temperature field within the solid portion of the hollow blade, while satisfying both boundary conditions of temperature and heat flux at the fixed outer blade surface, and the specified temperature boundary condition on the evolving inner surface. A first order panel method, coupled with Newton’s N-dimensional interation scheme, is used for the iterative solution of the unknown coolant/blade interface shape. Results are shown for a simple eccentrical bore pipe cross section and a realistic turbine blade cross section. The inverse design procedure is shown to be efficient and stable for all configurations that have been tested.