The present paper investigates drag reduction on a rectangular bluff body by employing base flaps and controlling flow separation with fluidic oscillators. Wind tunnel experiments are conducted to assess the influence of various parameters. The flap length has to be sufficiently long to shift the wake structures far enough downstream away from the base plate. Any additional increase in flap length does not yield any further benefits. The flap angle has to be large enough to provide a sufficient inward deflection of the outer flow. If the angle is too large, actuation becomes inefficient due to the pressure gradient imposed by the opposite side of the base perimeter. Furthermore, the flaps at high deflection angles provide additional area for low pressure to act in the streamwise direction and therefore negate the positive effects of actuation. The required actuation intensity is best governed by the ratio between jet and freestream velocity for varying oscillator spacing. For a flap angle of 20°, the smallest net drag is obtained at a velocity ratio of 4.5. Furthermore, the optimal velocity ratio for the most efficient drag reduction changes linearly with flap angle. Smaller flap deflections require a smaller velocity ratio for optimal control at different oscillator spacing. A net drag reduction of about 13 % is measured at a flap angle of 20° when the drag is corrected by the momentum input. Even if the measured drag is conservatively corrected by the energy coefficient, a net improvement of 7 % is achieved. For the current setup, the most efficient drag reduction is still obtained at smaller flap angles with a lower momentum input. However, the presented results support the general feasibility of this drag reduction approach with significant room left for optimization.
Experiments in Fluids – Springer Journals
Published: Jul 15, 2015
It’s your single place to instantly
discover and read the research
that matters to you.
Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.
All for just $49/month
Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly
Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.
Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.
Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.
All the latest content is available, no embargo periods.
“Hi guys, I cannot tell you how much I love this resource. Incredible. I really believe you've hit the nail on the head with this site in regards to solving the research-purchase issue.”Daniel C.
“Whoa! It’s like Spotify but for academic articles.”@Phil_Robichaud
“I must say, @deepdyve is a fabulous solution to the independent researcher's problem of #access to #information.”@deepthiw
“My last article couldn't be possible without the platform @deepdyve that makes journal papers cheaper.”@JoseServera