Lift and Drag of Kayak Rudders
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AbstractThis master's thesis studies the kayak rudder flow phenomena and uses analytic, numerical and experimental methods to describe the force coefficients of kayak rudders. Also an analysis of the sport of flatwater kayaking is conducted – amongst others with regard to the motion of the kayak hull and with regard to the propulsion. The former is based on measurement data of a K1 kayak. Further the focus is put on the rudder, and the gained knowledge finds e.g. utilization in modeling of the dynamic angle of attack.
Simulations based on CAD-data of a kayak rudder type are conducted (mostly RANS models) and discussed. Assumptions in this framework are that the boundary layer of the kayak hull is not accounted for and that possible effects of a transitional flow are not incorporated. Naturally, also the process and the solutions used to face the challenges of the grid development are described. Furthermore, a comparative analysis of different simulations (meshes, turbulence models and two sizes of the rudder) is undertaken. The main outcome are force coefficients and lift-to-drag ratios. They are based on angles of attack: 0o ≤ α ≤ 7.5o and found for three different Reynolds numbers.
These force coefficients are compared to analytical methods and discussed in the context of general flow phenomena and its modeling. The mainly discussed and derived analytical methods are slender body and lifting line theory (SBT & LLT). If the known error of LLT at small aspect ratios is empirically taken into account, the simulation results are in excellent agreement with the LLT. However, all of the studied sizes of the kayak rudder exceed the slenderness approximation of SBT. The simulation results are combined with the study of the kayak-hull motion, and the approximate dynamic power loss caused by the rudder is deduced. For the smallest rudder that is approximately 1.2 W.
In addition, an experiment is designed and build up to measure lift and drag of kayak rudders. First runs are conducted. They deliver a reasonable preliminary result for the drag force at zero angle of attack (compared with the simulations), but could unfortunately not be pursued further.
This master's thesis was not part of any ongoing project, and one can conclude that a further study in the field of kayak rudders most certainly could benefit from the achievements of this work.