DETERMINING THE EFFECT OF NOZZLE GROOVE ON THE FLUID FLOW THROUGH VISCOUS 2D PLANAR FLUID

Reem Ahmed1, Obai Younis2,3*, Ali Mohammed Hamdan4, Dania Ahmed3, Ali Ahmed Ali5, Ibrahim Ahmed6 1Elgeraf sharg Technical College, Department of Mechanical Engineering, Sudan 2Prince Sattam Bin Abdulaziz University, College of Engineering at Wadi Addwaser, Department of Mechanical Engineering, Alkharj, Saudi Arabia 3University of Khartoum, Faculty of Engineering, Department of Mechanical Engineering, Khartoum, Sudan 4University of Bahri, Department of Mechanical Engineering, Bahri, Sudan 5Abdulatif Alhamad University of Technology, Faculty of Engineering, Sudan 6Sudan University of Science and Technology, Department of Nuclear Engineering, Sudan


INTRODUCTION
Nozzle device is used for controlling the characteristics and direction of flowing fluid that increases its velocity as it enters or leaves an enclosed pipe or chamber. The nozzle is configured for a bi-directional flow, where pressure decrease in one direction increases the pressure of fluid in the other direction [1]. It is just like a tube or pipe of a definite cross-sectional area used to modify or direct the fluid flow. Therefore, nozzles play an essential role in controlling the flow rate, direction, speed, shape, mass, and pressure of stream emerging from them [2]. The velocity of the fluid within a nozzle increases at the cost of its pressure energy. The primary purpose of the nozzle is to restrict flow that builds up pressure, which is used to project the water stream. One restriction in the form of correct nozzle size is maintaining fluid flow and developing optimum pressure and velocity. For instance, the spray nozzle works at high pressure as the liquid is supplied to a swirl chamber through tangential holes. The liquid in the form of a thin conical sheet is discharged from the nozzle exit orifice and empties into the ligaments [3]. There are various sizes, styles, and shapes of nozzles with a large number of combinations that can be used to encounter the hydraulics problem on the fire ground [4]. The combination of nozzles with different engineer-ing applications is used to generate sprays and jets [5]. They are also widely used as aviation systems, maritime systems, automotive systems, and industrial systems as single equipment or part of equipment [6]. The effect of nozzles on flow characteristics in the spiral nozzle was investigated by Matsuo et al. [7] using an annual slit. The study used velocity distribution downstream of the nozzle exit that was compared with the computational results. Similarly, the flow characteristics of jet expansion pipe nozzles were investigated using the flow visualizations technique [8]. A review was carried out for a free jet from the round pipe installed with a collar at the jet exit. The results demonstrated no difference in jet spreading rate of pipe nozzle with collar and the conventional jet i.e., pipe nozzle without the collar. However, the conventional jet was much smaller than the jet from pipe nozzle with collar. Another study conducted by Alam et al. [9] investigated the impact of flow parameters at nozzle exit by stimulating turbulent flow using Reynolds-averaged Navier-Stokes (RANS) equations via nozzles of different dimensions. The results showed that the dimension of nozzle significantly affected the discharge coefficient. Similarly, Mohamed et al. [10] also studied pressure influence on the flow characteristics using RANS and two transport equations for modelling turbulence. The results showed T that there is a numerical simulation of the compressible flow in a convergent-divergent nozzle. The mechanism of inflow nozzle using direct numerical simulation (DNS) on spatially evolving round jets for the laminar and turbulent jet was investigated by numerous studies [11,12]. The results showed that it is essential to allow inflow entrapment in the simulation of turbulent jets. Various studies [13,14] illustrated a shock wave position for various pressure ratios by investigating different shapes of nozzles using the numerical investigation method. The results showed a significant impact of nozzle geometry on the flow structures, including the shock wave location. The structure of spray and distribution of particle size at nozzle exit was determined by Hespel et al. [15]. The results demonstrated that the atomization process and exit of fluid from the nozzle depend on cavitation. Moreover, the significance of nozzle geometry on subsequent atomization and fluid flow was validated by Agarwal and Trujillo [16], Zhang et al. [17], and Kumar and Sahu [18]. These results may correspond to the study conducted by Satyanarayana et al. [19], showing that fluid properties significantly depend on the cross-section of the nozzle that further affects the flow within the nozzle. Experiments on two-dimensional nozzles were also performed by Mashida and Sou [20] and Sou et al. [21] for analyzing cavitation in liquid jets under different Reynolds number and cavitation condition. Another study in 1999 was conducted by Badock et al. [22], who focused on the impact of nozzle geometry and internal flow on the velocity of fuel droplets and spray characteristics. However, these studied failed to conclude some promising results. Considering these failures, Hespel et al. [15] aimed to determine particle size distribution and spray structure close to nozzle exit. The results revealed the significant role of cavitation in the process of atomization and exit of liquid and ambient gas from the nozzle. Only a few studies have mainly focused on the numerical simulation of flow within the nozzles. A recent study by Liao and Deng [23] conducted a numerical simulation of nozzle water jet to analyze exit nozzle diameter, length of the cylindrical section, and convergence angle of the nozzle water jet. The results demonstrated that there is a significant effect of hydraulic cutting on the optimal nozzle parameters. Recently, it is observed that alterations are required in building sizes and elevations in case of fire for maintaining water velocity and flow. Fire can cause loss of lives and monetary loss; therefore, it is essential to manage it with new techniques to prevent hazardous effects. It is believed that more water with increased velocity helps in eliminating obstacles on the way during firefighting. These changes are only possible by generating some new technique. Therefore, there is a need to focus on the effects of nozzle shapes on water flow characteristics in firefighting nozzles with grooves of different dimensions. The present study evaluates the impact of nozzle groove on fluid flow through the viscous 2D planar fluid.

METHODS
The main stages of study analysis were; pre-processing, simulation, and post-processing. The initial phase of modelling, i.e., the pre-processing step, mainly include; defining geometry, mesh generation, defining boundary conditions, and solver parameters. Constructed models are used at the stimulation stage; whereas, analysis and visualization of the obtained results are conducted at the post-processing stage in the form of contours.

Defining nozzle dimensions
The designing of nozzles is done using SolidWorks software that was modified to introduce groove shaped nozzles, each consisting of six different designs ( Figure  1). These figures show multiple shapes of grooves with different dimensions and locations. The dimensions and distance of grooves from the nozzle exit are illustrated in Table 1.  The nozzle base model used in this study is similar to the one used by Zhang et al. [24]. All the nozzles presented in this study had these dimensions; 141.96 mm in length, 50 mm in diameter at the inlet, and 20 mm diameter at the outlet. The flow field considered in this case is steady, incompressible, and possess turbulent isothermal flow, with tensor form as follows in equation (1);

Type
shows the formula to calculate the equation of incompressible viscous fluid motion; The different geometries of nozzles set in ANSYS FLU-ENT-Design Modeler platform specify the physical boundaries of the fluid. The present study selected type 2D, and each dimension for every nozzle were defined according to the model. The nozzle models for grooves are shown in Figure 2; whereas, the geometries are illustrated in Table 2.

Meshing and Boundary
The nozzle structure is axisymmetric, which comprises

Model 2a
One groove with dimensions of 1×1 mm and distance from nozzle exit 10 mm.

Model 2b
One groove with dimensions of 1×1 mm and distance from nozzle exit 15 mm.

Model 1c
One groove with dimensions of 2×2 mm and distance from nozzle exit 10 mm.

Model 2d
One groove with dimensions of 2×2mm and distance from nozzle exit 15 mm.

Model 2e
Double grooves with dimensions of 1×1 mm, 7mm distance for first ring and 15mm for second ring from nozzle exit.

Model 2f
Double grooves with dimensions of 2×2 mm, 7mm distance for first ring and 15 mm for second ring from nozzle exit.  The velocity of the fluid at nozzle entrance is maintained at 20m/s; whereas, the boundary condition is axisymmetric on the axis and outflow is measured accordingly. Appropriate boundary conditions that describe the physics of the fluid flow need to be defined in the CFD solver. It is considered that the nozzle has an inlet and an outlet. The inlet pressure is eight par for the first case, 10 bar for the second case and 12 bar for the third case. The nozzle outlet pressure is 1.10235 bar. For walls condition, the nozzle, rings, and grooves walls are considered hydraulically smooth, so the boundary condition at the wall is described by the 'no-slip condition', which is the relative velocity between the wall and the fluid is set to zero. Flow analysis was conducted in the steady-state mode for all models.

Mesh dependence study and validation
For the mesh dependence study, three different number of mesh were tested, coarse, medium and fine as shown in Table 3. Figure 3 shows the volume flow rate computed at three different pressure values (8, 10 and 12 bar) for using the three different types of mesh mentioned in Table 1. It can be noticed that the results achieved by medium and fine mesh are almost identical. Therefore, the medium mesh is selected as a reference mesh number for all cases in this study. Validation is the primary mean for evaluating the accuracy and reliability in computational simulations. A well-documented benchmark experimental or numerical data must be used to validate the process that assesses modelling uncertainty. To validate the numerical approach utilized in this study, the obtained CFD results were compared with the numerical data of Zhang and Zhu [24]. Figure 4 presents the comparison between the current study and Zhang and Zhu [24] for axial velocity component. It is clear that a very good agreement between the results of current study and Zhang and Zhu [24] is obtained.

RESULTS AND DISCUSSION
The effect of groove dimensions 1×1 (mm) and location 10 mm at 8 bar, 10 bar and 12 bars, in velocity of water during flow in the nozzle is depicted in Figure 5. The figure shows that velocity increased with increasing in pressures proportion relationship, which clearly explains that the groove has no effect on velocity as it increases due to increase in pressure. This is because the groove reduces the velocity by increasing surface area. Figure 6 shows the effect of groove dimensions 1×1 (mm) and location 15 mm at 8 bar, 10 bar and 12 bars, in velocity of water during flow in the nozzle. The representation shows that velocity increased with increase in pressures proportion relationship. Therefore, it can be stated that the groove has no effect and velocity mainly increases due to increasing pressure as the groove reduces the velocity by increasing surface area.  Figure 7 illustrates the effect of groove dimensions 2×2 (mm) and location 10 mm at 8 bar, 10 bar and 12 bars, in velocity of water during flow in the nozzle. The velocity and pressure increase in a proportional relationship. The figure clearly shows that groove has no effect on the velocity because the groove reduces the velocity by increasing surface area. Figure 8 shows the effect of groove dimensions 2×2 (mm) and location 15 mm at 8 bar, 10 bar and 12 bars, in velocity of water during flow in the nozzle. This figure shows no effect on velocity because the groove reduces the velocity by increasing surface area.  Figure 9 illustrates the effect of double rings dimensions 1×1 (mm) and location 7 mm for the first and 15mm for second ring from the exit at 8 bar, 10 bar and 12 bars, in velocity of water during flow in the nozzle. The velocity increased with increasing pressures in a proportional relationship. There was no effect of increasing pressure on the velocity because the groove reduces the velocity as the surface area increased. Similar to the previous settings, Figure 10 also shows proportional relationship between increasing velocity and pressure. The results clearly demonstrate that there is negative effect of all dimensions and distance of groove location on the velocity of water during flow, at different pressure 8, 10, and 12 bar. This might be due to increase in surface area that decreases the velocity. There is no significant effect of groove on the velocities and turbulence intensities, as observed by comparing the corresponding plots because of experiencing much stress across the nozzle all the way up to the ringed nozzle exit. These results are in agreement with Yu et al. [5] as the study reported little effect of groove extending or exit the nozzle on the characteristics of fluid flow. It is of significance, as understanding it will help in considering its effect in firefighting, so that necessary changes in the model can be suggested. The aerodynamic performance of micro lobed nozzles ejectors of different dimensions was compared in an experimental and numerical study by Shan et al. [25]. The study used the k-ε standard turbulence model based on Reynolds-Averaged Navier-Stokes (RANS) simulations and showed significant impact of nozzle shape on the fluid downstream. Another similar study by Babu and Mahesh [26] studied the impact of inflow condition on the ambient fluid exiting the nozzle in a jet. The study failed to emphasize on the significance of initial conditions as the fluid exits the nozzle. On the contrary, the present study has drawn numerous findings and conclusions regarding certain physical and methodological aspects of fluid flow through a nozzle. The study also showed significant impact of nozzle shape on the exit conditions in the post-contraction region. A similar study by Yu et al. [5] compared the experimental data to investigate the impact of nozzle geometry on the turbulence characteristics of fluid flow through the nozzles. It is also likely that the analytical model of the pressure attributes is authentic and beneficial to obtain an insight of the physical mechanism [27]. Moreover, the passive control device can control the base pressure, which result in an improvement in the base pressure and mitigating the base drag. In addition, passive control is very effective and efficient whenever there is preferable pressure gradient at the nozzle exit [28,29]. The results demonstrated that presence of ring required increased inlet pressure for moving fluid through the nozzle as it increases the mean velocity and turbulence at the exit. These results are somewhat consistent with the present study that showed rings modifying the nozzle shape have significant impact on velocity. The present study has investigated the effect of different nozzle shapes on fluid flow characteristics in firefighting nozzles. There was no effect of groove design with dimensions 1×1 (mm) and location 15 mm at 8 bar, 10 bar and 12 bar because increase in surface area reduces the fluid velocity. These results demonstrate that there is no effect of the nozzle modified with grooves on the fluid velocity. These results exhibit good expectations about the use of rings to increase velocity of water that further improve nozzles operation in the same dimension.
The study has demonstrated that flow quantities in any region were not changed by extending the nozzle by one nozzle exit diameter. Slight change in the wall pressure is likely to be observed by cutting groove in the proximity of exit. This is clearly explained by the present study as addition of ring changes the pressure field in the post-contraction zone. The baseline nozzle with same flow rate imposed on nozzle was not effective in increasing the mean velocity of fluid in the jet. These findings suggest that inserting grooves without rings do not present promising results in achieving higher mixing efficiencies in the baseline nozzle, as it creates exit flow that is conducive to mixing. However, the future studies need to use the model developed in this study to assess the effect of water separations on velocity with inclusion of more grooves along with rings.