LIQUID WATER AND FLOW TURBULANCE CHARACTERIZATION OF THE PENN STATE ICING WIND TUNNEL

Open Access
- Author:
- Landge, Ameya S
- Graduate Program:
- Aerospace Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- April 26, 2018
- Committee Members:
- Jose Palacios, Thesis Advisor/Co-Advisor
- Keywords:
- Icing wind tunnel calibration
Turbulence intensity
Flow Angularity
Cloud uniformity
Median Volume Diameter (MVD)
SAE ARP 5905 - Abstract:
- Supercooled liquid water droplets present in clouds pose a threat to safety of aircraft. The water droplets impact on the surface and freeze, distorting the shape of the airfoil. The distortion of the airfoil shape increases drag and decreases lift. An event of unsymmetrical shedding can induce vibrations. Ice accretion on fuel vents prevents regular airflow and an increase in pressure may cause the fuel sacks to implode. Ice accretion on control surfaces may change the response of the surfaces. Ice accretion to sensors such a velocity probes is also extremely dangerous. Above issues create a need for Ice Protection Systems (IPS) to be installed onboard any aircraft. Design of Ice Protection System (IPS) is a complex iterative procedure and current modeling tools do not accurately predict the behavior of any particular system. The models can be tested in flight, on the ground and in icing wind tunnels. Inflight tests pose a risk to human life and ground icing tests may not be representative of in-flight icing conditions. Icing wind tunnels are a reduced cost option to test IPS prior to mandatory flight testing for certification purposes. To ensure the data collected for IPS and icing research is accurate it is of importance to ensure certain aerodynamic parameters of the wind tunnel are within pre-established guideline limits. The goal of this research is to calibrate the liquid water content (LWC) and flow turbulence in the vertical test section of the newly built Penn State Icing Tunnel (PSIT) for Appendix C conditions. The calibration was performed following the guidelines and limits specified in SAE Aerospace Recommended Practices (ARP) 5905. Initially, nozzle locations were identified to give a uniform cloud in the cross-section. A uniform cloud of 11 inch by 11 inch was obtained in the center of the tunnel section. Four NASA standard nozzles are used to get the even cloud. It was demonstrated that as the speed of air increased in the cross-section the uniformity decreased from 18 inch by 18 inch to 11 inch by 11 inch. The uniformity tests were followed by LWC calibration tests. Supercooled water was sprayed only for two different airline pressures of 15 and 20 psig. For higher air pressures the water droplets froze on exiting the nozzle and fully glaciated ice crystals were obtained at location of evaluation (demonstrating the capability of the tunnel to generate both supercooled clouds and fully glaciated frozen droplets). The objective of the presented work focuses on the calibration of supercooled clouds only (14 FAR Part 25 Appendix C conditions). Initial particle size calibration was conducted in the cross-section and further tests were carried out in the AERTS chamber to test the ability of the nozzles to produce different MVD particles sizes. Droplet sizes within and well beyond appendix C conditions were produced from 15 to 200 microns. Particle sizes below 30 microns were reproduced within ± 3 microns. Particle sizes beyond 30 microns and up to 200 microns were produced within 15 percent. Turbulence intensity tests were conducted at three different velocities 0 m/s, 17 m/s and 34 m/s. It was found that as speed increased, the centerline turbulence intensity decreased. Speed increase from 17 m/s to 34 m/s dropped the turbulence by 31.25 percent at centerline from 3.84 percent to 2.64 percent. At 17 m/s, an average increase in turbulence intensity in the cross-section was observed of about 25 percent when air flow through the nozzle was turned on. At 34 m/s, 0.5 percent average increase was observed. The turbulence intensity on average in the cross-section is within guideline limit but certain locations have turbulence intensities higher than the limits. However, as no tests are expected to be performed so close to the walls of the cross-section, it is of little concern. Flow angularity tests were carried out at 17 m/s. The measurement locations were limited due to length of the probe. The yaw angle was read from the protractor installed on the instrument. It has a least count of 0.2 degrees and was recorded less than 0.2 degrees at all the points. The average flow angle for the cross-section is 2.7 degrees and increased by about 13 percent to 3.05 degrees when air flow through the nozzle was turned on. The guidelines prescribe a limit of 3 degrees. As the case with turbulence intensity, some locations showed higher flow angularity but are not of grave concern.