Numberical Research On A New Type Vertical Axis Lift-drag Hybrid Wind Turbine

As regarded as a renewable energy, wind energy has the advantage ofnon-polluting, abundant storage, less investment but quick profit. Depletion of thefossil fuels and other non-renewable energy, enables countries to intensify the windpower technology’s study. The share of wind power generation occupies anincreasingly important position in the energy market. Because the running ofvertical axis wind turbines isn’t affected by wind flow direction, researchers take moreinteresting in the vertical axis wind turbine in the field of small wind power.Therefore, the numerical study of this wind turbine is a very important issue.The Lift-drag hybrid wind turbine this essay mentioned is installed two kinds ofwind wheel blade, one is resistance difference power type which placed close to therotation shaft,the other one is lift force type in the outer circle. One of the main themeof this essay work is to verify if the combination of these two known wind wheelscan make out additive effect. Lift force vertical axis wind turbine blade has H typeand Ф type without connecting rod, generally its blade profile is airfoil section profile.There are many kinds of resistance difference power wind wheel, and the commonstyle is Savonious type (or S shape) and other derived types based on it. The twokinds of vertical axis wind wheel both have their respective advantages anddisadvantages. Lift force type turbine owns relatively higher rotating speed, thus candirectly drive some small magneto electric generator sometime. But its startingperformance isn’t good enough, so usually it needs external equipment to drive up tothe running speed. The resistance difference wind wheel always has broaderwindward area, so make it easy to getting start with bigger initial torque,unfortunately the most suitable tip speed ratio usually less than1.0, therefore couldn’twidely be applied in electricity generation. The question this essay discussed anddemonstrated is verifying if the combination of inner resistance type and outside lifttype can produce complementary advantage, which means if the hybrid wind turbinecan have relative bigger starting torque and higher running rotate speed. To achievethis target, this essay begins from the computer simulation of the resistance differencewind wheel blade, creates the two-dimensional model of a S shape blade which has piece thickness, and then designs a new double S shape resistance difference windwheel owns same rotation radius as the S shape (there are two blades, each single hasS shape outline, and between them placed a guide vane).I select the RNG k-ε turbulence model and the corresponding calculation settings,to support my verification and design work. The main work begins from the computeand contrast of the two resistance type blade. Then place the same rotational annularfluid zones of4lift type blades outside the outline of inner rotational round zones ofresistance type blade, and make the comparison of the two hybrid wind wheel sampleslater. Comprehensive comparison shows the new designed double-S shape resistancetype blade in group with4lift type blades have better performance than the former Sshape blade’s combination plan, while the output power has obviously elevated after acertain speed and the best running tip speed ratio already bigger than1.0.Followed by the fact, I work on several other groups of two dimension Fluentsimulation. In these hybrid wind wheel groups, the chord lengths of the lift type bladeare different, and the calculations share same CFD settings. The obtained torque-tipspeed ratio profile and power-tip speed ratio profile of these groups both show the550mm chord length can get the best combined effect while using with the double-Sshape resistance type blade, as the effective working range of rotation speed is wider.Thus I make this conclusion as the basis of further optimization of the design. Whileat this time, I have already used to the manipulation of every software involved inmodeling and simulation, so I set up an isight-FD optimization platform to integrateall these software creating an automatic execution of process. I select three geometricvariables as the optimization design variables, including the match angle between thedouble-S shape resistance type blade and the lift type blade, and the offset distancesbetween two inner resistance blades in X axis direction and Y axis direction. In thisisight-FD platform, I take advantage of the MIGA(Multi-Island Genetic Algorithm),and set the average torque as the design objective, thus make the optimization workbe in progress.After that, I construct the three dimension solid model on the basis of the twodimensional optimized hybrid wind wheel, and then build up the flow field model inthree dimension space, in purpose to study the wind wheel’s aerodynamicperformance better close to the actual situation. The numerical simulation in threedimension applies CFX, relying on the moving mesh technique I create the sliding interface to achieve the unsteady simulation of rotational motion just as the sameprinciple as in two dimensional situation. The study work in three dimension, besidesthe straight blade directly stretched by the plane leaves, I also have a try of internalresistance blade’s twisting design, it means stacking the profiles deflected into a spiralconfiguration. To verify if this new design can play to improve the power outputcharacteristics or enhance the effect of performance, I do some numerical calculationwork. After that, I continue the three-dimensional optimization way, test the sweptblade design which rotating the lift blade’s cross-sections a certain angle alongcircumference to stack up. In the same calculation conditions, compare with thepreceding straight blade hybrid wind wheel, and assess its improved results. Thecomplete design process discussed in this paper will provide useful experience andilluminate the direction of future vertical axis wind wheel’s innovations andimprovements.