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Simulating Small VAWT
Hi
As part of my final year individual project, I’m tasked with recreating VAWT wind tunnel experiments by simulating them with QBlade. I’ve attached screenshots of the experimental model and the model I have recreated in QBlade. Looking at the example projects and other uses of QBlade, they tend to be on a much larger scale than that of the model I am using. The blades on my VAWT model are only 16cm and with a 4cm chord.
I was just curious if there is anything I should be considering due to my model being on a much smaller scale. I appreciate that sometimes just being able to create something within a software isn’t an indication that it is valid and will produce useable results.
Thanks,
Luke
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Hi Luke,
in general, turbines of any size can be simulated in QBlade. However, the small scale of your design introduces a few specific considerations:
- Reynolds Number:
The Reynolds number for your design will be significantly lower compared to conventional turbines (in the order of 1e3, compared to 1e6 for large turbines) . This presents challenges in obtaining high-quality polar data, as low Reynolds numbers can lead to effects such as laminar separation bubbles that influence performance. Additionally, the airfoils glide ratio will likely be quite low compared to airfoils operating at high Reynolds numbers.When using XFoil for simulations, I recommend setting both the “Forced Top Transition” and “Forced Bottom Transition” values to zero. This enforces a turbulent boundary layer originating from the leading edge, which is crucial for more realistic modeling at low Reynolds numbers.
- Rotational Rate and Time Step:
Due to the small rotor radius, your design will require a high rotational rate to achieve a given Tip Speed Ratio (TSR). Consequently, when performing time-domain simulations, you will need to use very small timesteps to sufficiently resolve each rotor revolution.
Aside from these specific points, the turbine can be treated like any other turbine design within QBlade.
BR,
David
