טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentYablochkin Efim
SubjectHigh-Speed Hot-Wire Anemometry Towards Independent
Characterization of Instantaneous Flow Quantities
with Minimal Calibration
DepartmentDepartment of Aerospace Engineering
Supervisor Dr. Beni Cukurel


Abstract

The present work is divided to theoretical and experimental parts. The theoretical part outlines an optimization method for selection of wire temperatures and diameters of constant temperature (CT) hot-wire anemometry probes geared towards decoupling of velocity, density and total temperature perturbations in transonic flow conditions. The experimental part focuses on developing, building and utilization of a simple lab-table sized operational calibration system and an in-house multi hotwire probes with extractable interchangeable heads manufacturing capability culminating in calibration and validation experiments.

Historically, hotwire measurements of density, velocity and temperature fluctuations in transonic flows are challenging due to the complexity of calibration and difficulties in obtaining a probe with favorably conditioned sensitivity matrix. The current theoretical study relies on evaluation of wire voltage-sensitivities to density, velocity and total temperature perturbations, based on universal empirical correlation for heated cylinders in compressible flow. In order to maximize the signal to noise ratio (SNR) of the decoupling, a two-step optimization-sifting procedure is developed. The first-step optimization maximizes a value function geared towards lower sensitivity-matrix condition-numbers, better robustness against wire temperature-setting errors and large sensitivities. From the resulting Pareto front, the second step sifts further through the candidate probes by decoupling simulated noisy voltage and ranking the probes by their decoupling quality. The performance of the optimal wire temperatures and diameters combination is contrasted against probes naively selected from the parameter space. According to the artificial data decoupling, only the optimal probes enable the decoupling with reasonable SNR. The theoretical part of the research effort culminates with proposed guidelines in order to define a probe with desirable properties, applicable across a wide range of transonic flow conditions.

In the experimental part, a detailed description of the experimental calibration-system is presented. The system is built entirely from scratch as part of the work towards this thesis. The experimental setup includes a jet calibration system with mass flux controller and a heater for temperature control, an angular probe positioning system controlled by “Arduino“, pressure and temperature sensors, “LabVIEW” based “Ni” data acquisition, a 4-wire HW probes with extractable interchangeable heads manufactured in-house, vacuum pump and a vessel for the probe to measure conduction losses and an “AALabs” Hot wire Anemometry “AN-1003” System.

Following the construction and validation of the experimental setup, calibration and decoupling experiments are presented, using probe settings close to the optimal wire diameters and temperatures suggested by the optimization.