An experimental study on the characteristics of wind-driven surface water film flows by using a multi-transducer ultrasonic pulse-echo technique

Abstract

An experimental study was conducted to investigate the characteristics of surface water film flows driven by boundary layer winds over a test plate in order to elucidate the underlying physics pertinent to dynamic water runback processes over ice accreting surfaces of aircraft wings. A multi-transducer ultrasonic pulse-echo (MTUPE) technique was developed and applied to achieve non-intrusive measurements of water film thickness as a function of time and space to quantify the transient behaviors of wind-driven surface water film flows. The effects of key controlling parameters, including freestream velocity of the airflow and flow rate of the water film, on the dynamics of the surface water runback process were examined in great details based on the quantitative MTUPE measurements. While the thickness of the wind-driven surface water film was found to decrease rapidly with the increasing airflow velocity, various surface wave structures were also found to be generated at the air/water interface as the surface water runs back. The evolution of the surface wave structures, in the terms of wave shape, frequency and propagation velocity of the surface waves, and instability modes (i.e., well-organized 2-D waves vs. 3-D complex irregular waves), was found to change significantly as the airflow velocity increases. Such temporally synchronized and spatially resolved measurements are believed to be very helpful to elucidate the underlying physics for improved understanding of the dynamics of water runback process pertinent to aircraft icing phenomena.

Separation Control on a Bridge Box Girder Using a Bypass Passive Jet Flow

“…This kind of particle seeding has been a long established method. Identical fog machines, oils, and set-ups have been used in a number of previous studies (e.g., [18,[24][25][26][27]). In addition, as proposed in Samimy and Lele [28], that particle response could be well characterized by τ , the ratio of particle response time to the flow time scale (Stokes' number), and only particles with τ > 0.05 were found to misrepresent the flow features.…”

“…At positive attack angles, Case 5 was close to Case 0, while the other control cases achieved a distinct decrease. Figure 6 25.22%] for the lift, drag, and moment coefficient RMSs, respectively. Control cases 2-4 had a large decrease in the RMSs of the aerodynamic coefficients, while Case 4 had the best control effectiveness.…”

A Comparison Study on AC-DBD Plasma and Electrical Heating for Aircraft Icing Mitigation

“…Glaze icing is considered to be more dangerous since it usually leads to much more dramatic increases in drag and decreases in lift 3 . Although many efforts have been made in recent years [4][5][6][7][8][9][10][11] , aircraft icing remains an important unsolved problem that is threatening the aviation safety.…”

Experimental Study of the Dynamics of Water Film on an Aluminum Substrate under Wind Shear

“…The interfacial wavy structure of a gas-sheared liquid film was observed, and the droplet entrainment mechanism was investigated [28]. Zhang et al [29] measured the water flow over an airfoil by using a digital image projection technique under impinging aerosol droplet conditions (10~25m/s). Liu et al [30] quantified the transient behavior of the surface water transport process and clearly represented the relationship between the film thickness and the wind speed by using an empirical scaling law in low-speed situations.…”

“…There are several characteristics of shear-driven water film, such as micro-scale thickness, complex interfacial waves, high reflective surface, fast variation in time space and easiness of disturbution, which make the measurement of thickness complicated. Although with so many challenges, extensive research has been done on liquid film problems using various techniques, such as optical measurement method [27,29], planar laser-induced fluorescence imaging [28], laser focus displacement meter [31], and capacitance probe [32]. Although many experimental and theoretical studies were carried out to investigate the water film flowing, most of them considered the gravity driven films or the two-phase flow in a vertical or horizontal tube.…”