Advanced Instrumentation and Measurements Techniques for Near Surface Flows

Cadel, Daniel R.

Advanced Instrumentation and Measurements Techniques for Near Surface Flows

dc.contributor.author	Cadel, Daniel R.	en
dc.contributor.committeechair	Lowe, K. Todd	en
dc.contributor.committeemember	Borgoltz, Aurelien	en
dc.contributor.committeemember	Devenport, William J.	en
dc.contributor.committeemember	Paterson, Eric G.	en
dc.contributor.committeemember	Ng, Wing Fai	en
dc.contributor.department	Aerospace and Ocean Engineering	en
dc.date.accessioned	2016-09-21T08:00:44Z	en
dc.date.available	2016-09-21T08:00:44Z	en
dc.date.issued	2016-09-20	en
dc.description.abstract	The development of aerodynamic boundary layers on wind turbine blades is an important consideration in their performance. It can be quite challenging to replicate full scale conditions in laboratory experiments, and advanced diagnostics become valuable in providing data not available from traditional means. A new variant of Doppler global velocimetry (DGV) known as cross-correlation DGV is developed to measure boundary layer profiles on a wind turbine blade airfoil in the large scale Virginia Tech Stability Wind Tunnel. The instrument provides mean velocity vectors with reduced sensitivity to external conditions, a velocity measurement range from 0ms^-1 to over 3000ms^-1, and an absolute uncertainty. Monte Carlo simulations with synthetic signals reveal that the processing routine approaches the Cramér-Rao lower bound in optimized conditions. A custom probe-beam technique is implanted to eliminate laser flare for measuring boundary layer profiles on a DU96-W-180 wind turbine airfoil model. Agreement is seen with laser Doppler velocimetry data within the uncertainty estimated for the DGV profile. Lessons learned from the near-wall flow diagnostics development were applied to a novel benchmark model problem incorporating the relevant physical mechanisms of the high amplitude periodic turbulent flow experienced by turbine blades in the field. The model problem is developed for experimentally motivated computational model development. A circular cylinder generates a periodic turbulent wake, in which a NACA 63215b airfoil with a chord Reynolds number Re_c = 170, 000 is embedded for a reduced frequency k = (pi)fc/V = 1.53. Measurements are performed with particle image velocimetry on the airfoil suction side and in highly magnified planes within the boundary layer. Outside of the viscous region, the Reynolds stress profile is consistent with the prediction of Rapid Distortion Theory (RDT), confirming that the redistribution of normal stresses is an inviscid effect. The fluctuating component of the phase- averaged turbulent boundary layer profiles is described using the exact solution to laminar Stokes flow. A phase lag similar to that in laminar flow is observed with an additional constant phase layer in the buffer region. The phase lag is relevant for modeling the intermittent transition and separation expected at full scale.	en
dc.description.degree	Ph. D.	en
dc.format.medium	ETD	en
dc.identifier.other	vt_gsexam:9022	en
dc.identifier.uri	http://hdl.handle.net/10919/72968	en
dc.publisher	Virginia Tech	en
dc.rights	In Copyright	en
dc.rights.uri	http://rightsstatements.org/vocab/InC/1.0/	en
dc.subject	Doppler global velocimetry	en
dc.subject	particle image velocimetry	en
dc.subject	wind turbine aerodynamics	en
dc.subject	unsteady boundary layers	en
dc.title	Advanced Instrumentation and Measurements Techniques for Near Surface Flows	en
dc.type	Dissertation	en
thesis.degree.discipline	Aerospace Engineering	en
thesis.degree.grantor	Virginia Polytechnic Institute and State University	en
thesis.degree.level	doctoral	en
thesis.degree.name	Ph. D.	en