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Article

Experimental Investigation of Runback Water Flow Behavior on Aero-Engine Rotating Spinners with Different Wettabilities

by
Kuiyuan Ma
1,
Guiping Lin
1,2,
Haichuan Jin
2,*,
Xiaobin Shen
1 and
Xueqin Bu
1
1
School of Aeronautic Science and Engineering, Beihang University, Beijing 100191, China
2
Hangzhou International Innovation Institute, Beihang University, Hangzhou 311115, China
*
Author to whom correspondence should be addressed.
Aerospace 2024, 11(7), 591; https://doi.org/10.3390/aerospace11070591
Submission received: 19 June 2024 / Revised: 12 July 2024 / Accepted: 17 July 2024 / Published: 20 July 2024
(This article belongs to the Special Issue Deicing and Anti-Icing of Aircraft (Volume III))
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Abstract

:
The accumulation of ice on the aero-engine inlet compromises engine safety. Traditional hot air anti-icing systems, which utilize bleed air, require substantial energy, decreasing engine performance and increasing emissions. Superhydrophobic materials have shown potential in reducing energy consumption when combined with these systems. Research indicates that superhydrophobic surfaces on stationary components significantly reduce anti-icing energy consumption by altering runback water flow behavior. However, for rotating aero-engine components, the effectiveness of superhydrophobic surfaces and the influence of surface wettability on runback water flow remain unclear due to centrifugal and Coriolis forces. This study investigates the runback water flow behavior on aero-engine rotating spinner surfaces with varying wettabilities in a straight-flow spray wind tunnel. The results demonstrated that centrifugal force reduces the amount of runback water on the rotating spinner compared to the stationary surface, forming rivulet flows deflected opposite to the direction of rotation. Furthermore, wettability significantly affects the flow characteristics of runback water on rotating surfaces. As the contact angle increases, the liquid water on the rotating spinner transitions from continuous film flow to rivulet and bead-like flows. Notably, the superhydrophobic surface prevents water adhesion, indicating its potential for anti-icing on rotating components. In addition, the interaction between rotational speed and surface wettability enhances the effects, with both increased rotational speed and larger contact angles contributing to higher liquid water flow velocities, promoting the rapid formation and detachment of rivulet and bead-like flows.

1. Introduction

Under icing weather conditions, ice will accumulate on the surface of the aero-engine inlet components, obstructing the intake passages, reducing engine intake flow, and adversely affecting its efficiency [1,2]. In high-bypass-ratio aero-engines, common icing components include the rotating spinner, fan blades, splitter ring, booster stage blades, outer bypass stator blades, and inlet sensors [3]. The rotating spinner, located at the forefront of the engine, is typically the most severely affected by icing. The ice accumulation process and ice shape on the rotating spinner surface differ significantly from those on stationary surfaces, leading to the formation of unique ice structures such as needle ice and ice features [4]. Large ice chunks breaking off during flight have caused severe fan blade damage [5] and unbalanced rotor dynamics, leading to costly repairs and extensive maintenance.
The scientific literature contains few studies on the ice accumulation and anti-icing characteristics of aero-engine rotating spinners. For experimental research, in 1986, Belz et al. [6] utilized a high-sensitivity video imaging system to observe ice accumulation and ice shedding on the surface of a rotating spinner, providing the images of surface ice shape at different times. In the same period, the Central Institute of Aviation Motors (CIAM) in Russia conducted icing tests on the spinner of the Д-90A engine without anti-icing measures, analyzing the physical processes and characteristics of ice formation [7]. Chen et al. [8] investigated the impact of rotational speed on ice accretion, analyzing the causes of needle ice and ice feathers and their effects on the ice accumulation process. Hu et al. [9] conducted experiments on ice formation and thermal anti-icing on rotating spinners, obtaining surface temperature distributions and relatively rough water film coverage areas. Li et al. [5] experimentally studied the icing characteristics of scaled rotating spinners with three different shapes (conical, conical–elliptical, and elliptical). Using high-speed phase-locked and PIV techniques, they observed the dynamic icing process and the external flow field of the spinners, discovering that shape alteration changed the impact characteristics of liquid water, resulting in different icing properties, with the conical spinner accumulating the most ice.
In numerical simulations, various models have been developed to evaluate water film flow and icing, such as the Messinger model, Myers model, and SWIM model [10,11,12,13,14]. However, these models were developed for icing processes on stationary components and do not consider the effects of rotation. Some researchers have attempted to incorporate the influence of centrifugal force, caused by rotation, into the mathematical description of thin water film flow on the surfaces of icing components [15,16,17,18]. This approach aims to provide a more accurate depiction of thin water film behavior during the icing process on rotating surfaces, thereby enabling the simulation of icing on rotating components. Nevertheless, due to various assumptions and simplifications, most simulation results yield relatively smooth ice shapes that significantly differ from the actual ice shapes on rotating spinners, and the needle-like or feather-like ice formations in actual icing are challenging to replicate through simulations. This is because the flow behavior of runback water on rotating surfaces, influenced by the coupling of centrifugal and aerodynamic drag forces, differs from that on stationary surfaces.
Due to the unique geometric structure of the rotating spinner, aerospace engine companies such as GE, PW, and RR are increasingly considering the use of structural anti-icing technologies for the intake rotating spinners and fan blades of civilian high-bypass-ratio turbofan engines. Assisted by water-repellent coatings, these technologies leverage centrifugal forces to reduce ice accretion or facilitate ice shedding into the outer bypass duct for anti-icing purposes. Superhydrophobic surfaces, due to their unique wettability, are considered potential candidates for structural anti-icing. The superhydrophobic surface is defined as the surface with a contact angle greater than 150°. Various methods have been developed to create superhydrophobic surfaces, including deposition methods [19,20,21,22], spraying methods [23,24], sol-gel methods [25,26], etching methods [27,28,29], and template methods [30,31,32]. Researchers have studied the properties of superhydrophobic surfaces under static or quasi-static conditions, such as accelerating droplet shedding [33,34], delaying icing [35,36,37], and reducing ice adhesion [38,39,40]. However, the effectiveness of using superhydrophobic surfaces alone remains controversial due to their poor durability and tendency to fail [41,42,43]. In recent years, technologies combining superhydrophobic surfaces with heated anti-icing systems have gained attention [44,45,46,47,48], offering a new direction for achieving low-energy anti-icing in aero-engines [49,50]. To understand the performance and mechanisms of superhydrophobic surfaces for anti-icing, several studies have been conducted under static conditions, focusing on delaying ice formation [35,36,37] and reducing adhesion [38,39,40]. Overall, research on the anti-icing mechanisms of superhydrophobic surfaces has predominantly been conducted under static or quasi-static conditions, with the resulting data insufficient to fully validate the effectiveness of these surfaces in aero-engine anti-icing systems, particularly on rotating components. Our previous research [48] has demonstrated the feasibility of applying superhydrophobic surfaces to aircraft wings, showing that surface wettability primarily influences low-energy anti-icing by affecting runback water flow patterns [51]. For hydrophobic and superhydrophobic rotating surfaces, the involvement of wettability may cause unique behaviors in the flow, spreading, and shedding of runback water, significantly altering the icing and anti-icing characteristics of rotating spinners. Therefore, it is essential to study the runback water flow behavior on rotating spinners with different wettabilities to understand the icing characteristics and anti-icing mechanisms of superhydrophobic rotating spinners.
To address these limitations, we conducted an experimental investigation on the runback water flow behavior on aero-engine rotating spinners with different wettabilities in a straight-flow spray wind tunnel. The flow patterns of runback water on both stationary and rotating spinners were observed, and the influence of rotational speed and wettability on the runback water flow patterns was compared and analyzed.

2. Experimental Setup

2.1. Rotating Spinner Model

The structure of the rotating spinner model used in the experiment is shown in Figure 1. It is a 1/2 scale model of a spinner from a specific aero-engine, with a tail diameter of approximately 295 mm. Due to the size constraints of the spray wind tunnel test section, it is not possible to conduct experiments on the entire spinner model. Considering that when the spinner size is large, the areas of water droplet impact and ice accretion are mainly concentrated on the front section of the spinner, a simplified model is used. To ensure an appropriate blockage ratio while fitting within the test section dimensions, the front section of the spinner with a diameter of 150 mm is selected as the test specimen. The spinner has a conical shape with a cone angle of 72° and a blunt radius of 3 mm at the stagnation point on the front end. This simplified model allows for focused study on the relevant areas of ice formation and water droplet impact.

2.2. Surface Treatment

In this study, the runback water flow behavior on surfaces with significantly different wettabilities is investigated on hydrophilic (HPL), hydrophobic (HPB), superhydrophilic (SHPL), and superhydrophobic (SHPB) surfaces. As shown in Figure 2, rotating spinners with different surface wettabilities are prepared using various methods. The HPL rotating spinner is made from polished 2A12 aluminum alloy, and the subsequent preparation of the other three surfaces also uses this as the original substrate material. The HPB rotating spinner is obtained by spraying black thermoplastic acrylic resin paint (SANO, J2A39, Shenzhen, China) on the surface of the 2A12 aluminum alloy spinner, which dries at room temperature with a coating thickness controlled between 40 and 60 μm. The SHPL rotating spinner is created by forming a black porous oxide layer on 2A12 aluminum alloy at room temperature through a solution immersion method [52]. The main components of the blackening solution are sodium sulfate and sodium carbonate. After surface treatment, the contact angle of the surface is about 10°, resulting in a superhydrophilic surface. The specific steps are as follows. The specimen is soaked in a metal cleaner for 2 min to remove surface oil, rinsed with clean water three times, soaked in the blackening solution for 5 min, and then rinsed with clean water three times. The SHPB rotating spinner is prepared by ultrafast laser ablation. The polished 2A12 aluminum alloy surface was ultrasonically cleaned for 10 min and dried using compressed air. After the pretreatment, periodic microgroove structures with a spacing of 30 μm were ablated by a femtosecond laser (Edgewave, FX200, North Rhine-Westphalia, Germany). The microstructures were designed using bionic wheat leaves. Subsequently, the processed surfaces are soaked in a 1 wt.% solution of fluoroalkylsilane (1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane) in ethanol for 1 h, and then dried in an oven at 60 °C for 3 h to obtain superhydrophobic properties.
The surface wettabilities were evaluated by the contact, and the results are shown in Table 1.

2.3. Straight-Flow Spray Wind Tunnel and Phase-Locked Observation Technology

The experiments were conducted in a self-built open-loop low-speed straight-flow wind tunnel at the Human–Machine and Environmental Engineering Laboratory of Beihang University. The wind tunnel included an aerodynamic system, water spray atomization system, and test section. Figure 3 shows the experimental setup used to investigate the runback water behavior on the rotating spinner. An air atomizing nozzle was installed in the stable section of the wind tunnel to generate microscale droplet spray impinging on the spinner with airflow to form the water film. The nozzle was connected to a water tank and an air compressor to form a continuous spray. The test section was composed of transparent acrylic panels with dimensions of 1000 mm × 400 mm × 300 mm (length × width × height), and the rotating spinner was fixed in the test section and driven by the brushless motor (QIWO, 650W-6000R, Taizhou, China). The rotational speed can be adjusted from 0 to 3000 rpm by the transducer.
Observing high-speed rotating surfaces presents significant challenges. Conventional observation methods, such as standard cameras, cannot capture the dynamic processes effectively. High-speed cameras are typically required, but their continuous recording is limited by buffer size, resulting in short monitoring durations and low post-processing and data transmission efficiency. Therefore, this chapter proposes a high-speed phase-locked observation technique for rotating components to dynamically observe the liquid water flow behavior on rotating surfaces. As shown in Figure 3, a laser tachometer (Monarch, PLT200, Brookfield, WI, USA) is used for non-contact measurement of the rotational speed of the spinner. It detects a reflective tape (Monarch, T5) placed on the rotating body, receiving a pulsed reflected laser signal from each rotation cycle and generating the TTL pulse digital signal. This TTL pulse signal is sent to the trigger port of a high-speed camera (Pco.dimax, HS4, Pittsburgh, PA, USA), which triggers the camera to capture images at the same phase of the rotating spinner, achieving phase-locked image acquisition. This method allows for time-series recording of the liquid water flow or icing process on the surface of the rotating spinner as it reaches the same position during each rotation.

2.4. Experimental Conditions

The experimental conditions are listed in Table 2. The wind speed is achieved by directly controlling the motor frequency using a drive (Asea Brown Boveri, Ltd., ACS510, Zurich, Switzerland). The wind speeds utilized in this study can be adjusted between 8 and 20 m/s while ensuring experimental safety and maintaining flow field quality. Therefore, the maximum wind speed of 20 m/s is selected for this study. The median volumetric diameter (MVD) of 30 μm, which is typical for icing conditions, is achieved by controlling the nozzle pressure. The liquid water content (LWC) is adjusted by varying the nozzle flow rate and can be set between 2 and 10 g/m3. For this study, a relatively high LWC of 3 g/m3, representative of icing conditions, is selected. The procedure involves initially adjusting the flow rate of the atomizing nozzle and the airflow speed in the wind tunnel to ensure that the wind speed and liquid water flow rate inside the tunnel reach the preset values and remain stable. Next, the high-speed camera is turned on, and both the light source and camera parameters are adjusted accordingly. The rotational speed is then set to the preset value, and the exposure time of the high-speed camera is adjusted to obtain a clear image, allowing for the recording of experimental data to commence. Once the atomizing nozzle valve and the compressor valve are opened, the spray is generated. After 60 s of data acquisition with the high-speed camera, the spray is stopped, the camera recording is halted, and the motor and centrifugal fan are turned off. This procedure is repeated for other rotational speeds or different wettability surfaces under the same environmental conditions.

3. Results and Discussions

3.1. Flow Patterns of Runback Water on the Stationary Spinner

In the experiments conducted in this study, it can be approximated that the flow pattern of runback water on the spinner is dynamically stable over extended spray periods, disregarding the microscopic features such as surface fluctuations. This assumption aligns with related research on stationary surfaces [53].
The runback water flow pattern on the stationary spinner is first examined for the control group. As shown in Figure 4, the stable runback water flow patterns on four different spinner surfaces at zero rotational speed are presented. In Figure 4a, on the superhydrophilic surface (SHPL), the liquid water uniformly spreads into a continuous film, covering the entire spinner surface. Figure 4b shows that on the hydrophilic surface (HPL), the water film is partially discontinuous, with dry patches, yet it still generally covers the surface. The thickness of the liquid film is thicker relative to the SHPL, as can be roughly judged from the images. As shown in Figure 4c, on the hydrophobic surface (HPB), runback water is distributed as discrete droplets adhering to the spinner surface without forming a continuous film. In Figure 4d, the superhydrophobic surface (SHPB) exhibits no observable liquid water and droplet adhesion, indicating that the water droplets rapidly shed away from the surface due to airflow drag force. The experimental phenomena are markedly distinct between groups, making quantitative data comparison challenging. Overall, as the surface contact angle increases, the coverage area of runback water decreases, and the water is more likely to form bead-like flows. Due to the relatively low wind speed in the experiments, no significant rivulet flow is observed on the stationary surfaces.

3.2. Flow Patterns of Runback Water on the Rotating Spinner

When the spinner rotates, the behavior of runback water on its surface changes due to rotational effects, significantly different from those in Section 3.1. As shown in Figure 5, the random single-frame images from the observation of liquid water flow on the HPL surface at different rotational speeds are extracted to analyze the flow patterns. As shown in Figure 5b–d, the centrifugal force generated by rotation causes the previously continuous water film on the HPL surface to form noticeable rivulets. These rivulets deflect opposite to the direction of rotation, indicating that the flow behavior is influenced by rotational effects. As the rotational speed increases, the rivulet phenomenon becomes more pronounced, with an increased number of finer rivulets and larger deflection angles, which is related to the increased centrifugal force. The deflection angle of the rivulets can be theoretically analyzed using velocity vector analysis and compared with experimental results, as discussed in Section 3.3. Additionally, it is observed that the runback water spreads to form a continuous film in the front edge region on the rotating spinner surface. As the rotational speed increases, the area covered by the continuous liquid film becomes smaller. The possible reasons for these observations include the centrifugal force generated by the rotation, which makes the runback water more prone to being shed away, thereby reducing the amount of liquid water on the surface and facilitating the transition of the liquid film into rivulet flows. Furthermore, the increase in rotational linear velocity enhances the relative velocity of the runback water to the airflow, increasing the airflow drag force and promoting the formation of finer and more numerous rivulets.

3.3. Effect of Rotational Speed on the Flow Path and Velocity of Runback Water

To understand the influence of rotation on the behavior of runback water, a theoretical analysis was conducted. The deflection of the rivulet flow is primarily attributed to the resultant velocity vector of the local tangential speed and the flow direction speed when droplets impact the surface. For a droplet impacting the spinner at a rotational speed n , the angle between the droplet’s velocity and the spinner axis θ u can be expressed as:
tan θ u = u r u g = 2 π n r x u g
where u r is the local tangential velocity, u g is the incoming airflow speed, and r x is the local radius of rotation. tan θ u represents the direction of the rivulet velocity, which corresponds to the slope of its trajectory. Thus, the flow path can be described by:
y l = ∫ − tan θ u tan 36 ° d x = − 0.019 n x 2
where y l represents the y-coordinate of the rivulet path corresponding to the x-coordinate.
The Gaussian mixture model is used to process the experimental time-series images of the flow to determine the rivulet flow paths at different rotational speeds. Taking the leading edge of the spinner as the coordinate origin, the points on the rivulet path with a starting point near y = 0 are extracted and fitted with a quadratic curve, as depicted in Figure 6. The dotted lines represent the theoretically estimated paths through the coordinate origin. If the slope changes of the experimental fitting curve match those of the theoretical curve, it indicates a good fit. Comparative analysis of the two sets of curves reveals that the experimentally observed circumferential deflection angles of the rivulet flows closely match the angles estimated using the velocity vectors, thereby validating the theoretical analysis and the experimental results. It is evident that as rotational speed increases, the centrifugal force also increases, leading to a greater deflection angle of the resultant velocity vector. This results in an increase in the absolute value of the coefficients in Equation (2), producing a larger deflection angle of the rivulet path. In addition, it should be noted that for the HPL surface analyzed here, although the increased centrifugal force results in a greater deflection angle, the surface energy remains high. Consequently, the centrifugal force does not overcome the surface adhesion force, and most of the runback water continues to flow along the surface without shedding away.
Through image recognition and analysis of high-speed phase-locked images, the displacement sizes of rivulet flow at various positions within the frame difference time range are statistically measured using frame differencing, and velocity values were obtained. As shown in Figure 7, the surface liquid water flow speeds within the x-coordinate range of 30 to 40 mm are statistically determined. It is observed that higher rotational speeds are associated with greater liquid water flow velocities. Specifically, at 1000 rpm, the flow speed is approximately 0.2 m/s; at 2000 rpm, it increases to approximately 0.4 m/s; and at 2500 rpm, it further rises to approximately 0.6 m/s. Curve fitting indicates that the relationship between rotational speed and flow velocity is nonlinear and proportional to the square of the flow velocity. As rotational speed increases, the rate of increase in flow velocity decreases. It suggests that the primary impact of rotation on flow behavior is manifested in both the magnitude and direction of velocity changes. The faster the rotational speed, the greater the change in both the direction and magnitude of the resultant velocity.

3.4. Effect of Wettability on the Flow Behavior of Runback Water on the Rotating Spinner

Figure 8 illustrates the flow patterns of runback water on the rotating spinners with different wettabilities at a rotational speed of 2000 rpm. Compared to stationary conditions in Figure 4, there is a noticeable reduction in the amount of surface liquid water and a decrease in droplet diameter, accompanied by the appearance of rivulet flows. The comparative analysis of the flow patterns across the four surfaces reveals that larger contact angles correspond to reduced observed quantities of surface liquid water. Comparing Figure 8b,c, it is evident that increasing surface contact angle causes the initiation and termination positions of rivulet flows induced by rotation to be closer to the front edge. For example, on the HPB surface, rivulet flow termination and detachment occur approximately 4 cm from the front edge stagnation point. This is because, as the contact angle increases, the adhesion force of the runback water on the surface decreases. Consequently, during the runback flow process, the water detaches from the surface under centrifugal force, reducing the observed amount of surface liquid water and shifting the appearance and termination of rivulet flows closer to the front edge. As shown in Figure 8d, under the combined influence of rotational effects and wettability, the superhydrophobic spinner surface shows no observable adhesion of liquid water. On rotating components, reducing surface wettability not only promotes the breakup of continuous liquid films in the flow direction but also facilitates the centrifugal shedding of runback water in the normal direction to the surface, further reducing the amount of water on the surface.
Using the same processing methods as described in Section 3.3, the liquid water flow velocities on different surfaces are obtained, as shown in Figure 9. For the SHPL surface, no distinct flow initiation point could be identified. Therefore, the propagation speed of surface waves is used as the flow velocity in the analysis. For the SHPB, no liquid water adhesion is observed, and thus, no data points are extracted. It is observed that flow velocity exhibits an exponential increase with the contact angle. Compared to the effect of rotational speed shown in Figure 7, the contact angle has a more significant effect on flow velocity. At lower contact angles (10°), the flow velocity remains relatively low, around 0.2 m/s. When the contact angle increases to approximately 90°, the flow velocity rises significantly to about 0.8 m/s. It is important to note that for rotating surfaces, the impact of wettability on the flow velocity along the surface is just one aspect; its influence on the detachment of liquid water in the normal direction is also significant. This aspect warrants further investigation using more advanced experimental or simulation methods.
Overall, the experimental results demonstrate that the rotational effect and surface wettability exert a mutually reinforcing influence on one another. Both an elevated rotational speed and a greater contact angle are conducive to a greater liquid water flow velocity, thereby accelerating the formation and detachment of rivulet and bead-like flows. Moreover, the increase in contact angle enhances the effect of the centrifugal force generated by rotation on the detachment of runback water, further reducing the quantity of surface liquid water. In terms of anti-icing, this results in a reduced heat transfer time for liquid water on the anti-icing surfaces and a decreased coverage of liquid water. Consequently, more liquid water can be shed away from the surface before freezing, thereby lowering the thermal load required by the anti-icing system and achieving effective anti-icing with reduced energy consumption.

4. Conclusions

An experimental investigation is conducted to analyze the runback water flow behavior on aero-engine rotating spinners with different wettabilities in a straight-flow spray wind tunnel. The stationary and rotating spinners with hydrophilic, hydrophobic, superhydrophilic, and superhydrophobic surfaces are examined. Dynamic images are captured using high-speed phase-locked observation techniques to reveal the influence of rotational speed and surface wettability on water flow patterns. The key findings are as follows:
(1)
On stationary spinners, continuous water films form on superhydrophilic surfaces, while no water adhesion is observed on the superhydrophobic surface.
(2)
On rotating spinners, rivulet flows start to appear on hydrophilic and hydrophobic surfaces. Increased rotational speeds lead to finer and more numerous rivulet flows. These rivulet flow paths exhibit circumferential deflection due to centrifugal and aerodynamic drag forces. The deflection angle primarily depends on the magnitude and direction of the resultant velocity. Additionally, the square of the rivulet flow velocity is proportional to the rotational speed.
(3)
Surface wettability affects runback water flow behavior in two ways. In the flow direction, an increase in contact angle leads to higher flow velocities, with runback water more likely to form rivulet and bead-like flows. In the normal direction, an increased contact angle allows centrifugal force to overcome surface adhesion more easily, promoting the detachment of runback water.
Future research can expand the parameter range and employ experimental or simulation methods to study the effects of surface wettability on runback water behavior under higher wind speeds and rotational speeds, to confirm the efficacy of superhydrophobic surfaces in rotating component anti-icing systems.

Author Contributions

Conceptualization, G.L.; Methodology, G.L., H.J. and X.B.; Software, X.S.; Investigation, K.M.; Resources, G.L. and X.S.; Data curation, X.S.; Writing—original draft, K.M.; Writing—review & editing, H.J.; Supervision, X.B.; Funding acquisition, H.J. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Key Laboratory of Icing and Anti/De-icing of CARDC (IADL 20230101), the National Natural Science Foundation of China (No. 12172029), Fundamental Research Funds for the Central Universities and 111 Project (B18002).

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

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Aerospace 11 00591 g001
Figure 1. Rotating spinner model.
Figure 1. Rotating spinner model.
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Figure 2. Rotating spinners with different surface wettabilities: (a) HPL surface, polished 2A12 aluminum alloy, which serves as the substrate material for the other surfaces; (b) HPB surface; (c) SHPL surface; (d) superhydrophobic surface.
Figure 2. Rotating spinners with different surface wettabilities: (a) HPL surface, polished 2A12 aluminum alloy, which serves as the substrate material for the other surfaces; (b) HPB surface; (c) SHPL surface; (d) superhydrophobic surface.
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Figure 3. Experimental setup of the runback water behavior on the rotating spinner investigation system.
Figure 3. Experimental setup of the runback water behavior on the rotating spinner investigation system.
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Figure 4. Extracted single-frame images to characterize the flow pattern of runback water on the stationary spinner (zero rotational speed): (a) formation of a continuous water film on SHPL surface; (b) water film with dry patches on HPL surface; (c) bead-like flow on HPB surface; (d) no droplets on SHPB surface.
Figure 4. Extracted single-frame images to characterize the flow pattern of runback water on the stationary spinner (zero rotational speed): (a) formation of a continuous water film on SHPL surface; (b) water film with dry patches on HPL surface; (c) bead-like flow on HPB surface; (d) no droplets on SHPB surface.
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Figure 5. The flow pattern of runback water on the rotating spinner at different rotational speeds: (a) stationary; (b) 1000 rpm; (c) 2000 rpm; (d) 2500 rpm. The rotation induces the rivulet flow on the surface, with the direction of deflection being opposite to the direction of rotation.
Figure 5. The flow pattern of runback water on the rotating spinner at different rotational speeds: (a) stationary; (b) 1000 rpm; (c) 2000 rpm; (d) 2500 rpm. The rotation induces the rivulet flow on the surface, with the direction of deflection being opposite to the direction of rotation.
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Figure 6. Flow paths on the spinner surface at different rotational speeds.
Figure 6. Flow paths on the spinner surface at different rotational speeds.
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Figure 7. Flow velocity of rivulets on the spinner surface at different rotational speeds.
Figure 7. Flow velocity of rivulets on the spinner surface at different rotational speeds.
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Figure 8. The flow pattern of runback water on the rotating spinner at 2000 rpm with different wettabilities: (a) SHPL; (b) HPL; (c) HPB; (d) SHPB.
Figure 8. The flow pattern of runback water on the rotating spinner at 2000 rpm with different wettabilities: (a) SHPL; (b) HPL; (c) HPB; (d) SHPB.
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Figure 9. Flow velocity of rivulets on the spinner surface at rotational speed of 2000 rpm.
Figure 9. Flow velocity of rivulets on the spinner surface at rotational speed of 2000 rpm.
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Table 1. Contact angle of four surfaces (mean ± standard deviation).
Table 1. Contact angle of four surfaces (mean ± standard deviation).
SurfacesSHPLHPLHPBSHPB
Contact Angle (°)Aerospace 11 00591 i001Aerospace 11 00591 i002Aerospace 11 00591 i003Aerospace 11 00591 i004
10.2 ± 571.8 ± 288.4 ± 2151.3 ± 2
Table 2. Summary of experimental conditions.
Table 2. Summary of experimental conditions.
Case No.Wind Speed (m/s)LWC (g/m3)Rotating Speed (rpm)Surface
120 ± 13 ± 0.50HPL
21000HPL
32000HPL
42500HPL
50SHPL
62000SHPL
70HPB
82000HPB
90SHPB
102000SHPB
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Ma, K.; Lin, G.; Jin, H.; Shen, X.; Bu, X. Experimental Investigation of Runback Water Flow Behavior on Aero-Engine Rotating Spinners with Different Wettabilities. Aerospace 2024, 11, 591. https://doi.org/10.3390/aerospace11070591

AMA Style

Ma K, Lin G, Jin H, Shen X, Bu X. Experimental Investigation of Runback Water Flow Behavior on Aero-Engine Rotating Spinners with Different Wettabilities. Aerospace. 2024; 11(7):591. https://doi.org/10.3390/aerospace11070591

Chicago/Turabian Style

Ma, Kuiyuan, Guiping Lin, Haichuan Jin, Xiaobin Shen, and Xueqin Bu. 2024. "Experimental Investigation of Runback Water Flow Behavior on Aero-Engine Rotating Spinners with Different Wettabilities" Aerospace 11, no. 7: 591. https://doi.org/10.3390/aerospace11070591

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