Design of a Velocity Measurement Device for Kayak Rudders an Experimental and Numerical Approach

Kirkedal, Nicolai Hede ; Krantz, Morten

4. term

Energy Engineering, Master

2018

2018-06-01

135

Dette projekt har to formål: for det første at udvikle en avanceret numerisk metode til at undersøge hydrodynamisk modstand i stille vand for kajakskrog, og for det andet at behandle, hvordan man måler fart/effekt på kajakker. Nuværende CFD-modeller (computational fluid dynamics) for kajakskrog køres ofte i stationær tilstand, hvor skroget antages at bevæge sig uden at ændre stilling. Det betyder, at heave (lodret bevægelse) og pitch (nikning/kipning) ikke indgår. Denne undersøgelse udvider rammerne ved at tillade ændringer i heave og pitch under simuleringen. Simulationsresultaterne blev kontrolleret mod et egenudviklet eksperiment. Projektet udvikler også en hastighedsmåler, der passer ind i kajakkens ror. Den bygger på et pitot-statisk rør, som måler hastighed ved at sammenligne trykforskelle. Placeringen af stagnations- og statiske huller er fastlagt ud fra analytiske og numeriske overvejelser. Hastighedsmålingerne fra roret blev valideret gennem forsøg i en vindtunnel. CFD-simuleringerne gav præcise resultater ved et Froude-tal på 0,45, med en fejl på under 5 %. Ved et Froude-tal på 0,56 var afvigelsen større, og modellerne undervurderede den samlede modstand med cirka 18 %. Ror-sensoren leverede pålidelige hastighedsmålinger med en fejl på under 8,5 % i forhold til referenceværdien.

This project has two aims: first, to develop a state-of-the-art numerical approach to study calm-water hydrodynamic resistance of kayak hulls; second, to address how to measure a kayak’s speed/power. Current CFD (computational fluid dynamics) models for kayak hulls are typically run in steady state, which means the hull’s position is assumed not to change. As a result, heave (up-and-down motion) and pitch (tilting) are not included. This study extends the framework by allowing heave and pitch to vary during the simulation. The simulations were checked against a custom-built experiment. The project also develops a velocity sensor that fits inside the kayak’s rudder. It works as a pitot-static tube, measuring speed from pressure differences. The locations of the stagnation and static holes were set using analytical and numerical methods. Velocity readings from the rudder were validated in wind-tunnel tests. The CFD simulations were accurate at a Froude number of 0.45, with less than 5% error. At a Froude number of 0.56, the deviation grew and the models underpredicted total resistance by about 18%. The rudder sensor produced reliable speed readings, with error below 8.5% compared to the reference.

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