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Bajracharya et al. (2008) did a field setting research and laboratory research to reveal the empirical relation between loss of efficiency due to sand particle led erosion of Pelton turbine. The authors measured the eroded needle profile after fixed operational hours of the runner (see Fig. 2). Figure 2: Erosion of Pelton turbine needle at Chilime HPS, Nepal (Adapted from Bajracharya et al. 2008)

Figure 2 Bajracharya et al. (2008) did a field setting research and laboratory research to reveal the empirical relation between loss of efficiency due to sand particle led erosion of Pelton turbine. The authors measured the eroded needle profile after fixed operational hours of the runner (see Fig. 2). Figure 2: Erosion of Pelton turbine needle at Chilime HPS, Nepal (Adapted from Bajracharya et al. 2008)

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Fig. 1 summarizes the erosion from two hydro power plants. Figure 1: Typical erosion in Pelton turbine parts (On left: Mel Norway On Right: Bucket of Khimti Powerplant, Nepal) Image Courtesy: Neopane et al. 2011.
Fig. 1 summarizes the erosion from two hydro power plants. Figure 1: Typical erosion in Pelton turbine parts (On left: Mel Norway On Right: Bucket of Khimti Powerplant, Nepal) Image Courtesy: Neopane et al. 2011.
Figure 3: Needle damage due to erosion at Chilime HPS, Nepal
Figure 3: Needle damage due to erosion at Chilime HPS, Nepal
Figure 4: Erosion in nozzle and needle (On left, erosion in nozzle ring of Andhi Khole HPP, Nepal and needle erosion in Khimti HPP, Nepal (Adapted from Neopane et al. 2011) Neopane et al. (2011), in review of erosion of hydraulic turbines have revealed the images of eroded nozzle and needle of Andhikhola HPS and Khimti HPS of Nepal. From the Fig. 4, it can be observed that there is uniform wear of the nozzle (in the needle seat) and scaly erosion is seen in the Needle surface.
Figure 4: Erosion in nozzle and needle (On left, erosion in nozzle ring of Andhi Khole HPP, Nepal and needle erosion in Khimti HPP, Nepal (Adapted from Neopane et al. 2011) Neopane et al. (2011), in review of erosion of hydraulic turbines have revealed the images of eroded nozzle and needle of Andhikhola HPS and Khimti HPS of Nepal. From the Fig. 4, it can be observed that there is uniform wear of the nozzle (in the needle seat) and scaly erosion is seen in the Needle surface.
Figure 5: Erosion study in coated needle (Image Courtesy: Andritz Hydro) Morales et al. (2017) experimentally studied about the erosion of Pelton turbine injector of Chivor hydroelectric plant, Columbia. The authors have also developed a test rig to study and develop empirical relation of nozzle-needle coatings and wear. The needle erosion of Chivor hydropower station has in depth erosion and is similar to that observed by Bajracharya et al. 2008. ANDRITZ hydro (Karandikar, 2015° performed the field test of HVOF Coatings to combat hydro abrasive erosion. The study reveals images (see Fig. 5) of coated and uncoated needles in a two nozzle Pelton turbine and concludes that the coated needle has four times longer life than the coated needle.
Figure 5: Erosion study in coated needle (Image Courtesy: Andritz Hydro) Morales et al. (2017) experimentally studied about the erosion of Pelton turbine injector of Chivor hydroelectric plant, Columbia. The authors have also developed a test rig to study and develop empirical relation of nozzle-needle coatings and wear. The needle erosion of Chivor hydropower station has in depth erosion and is similar to that observed by Bajracharya et al. 2008. ANDRITZ hydro (Karandikar, 2015° performed the field test of HVOF Coatings to combat hydro abrasive erosion. The study reveals images (see Fig. 5) of coated and uncoated needles in a two nozzle Pelton turbine and concludes that the coated needle has four times longer life than the coated needle.
Figure 6: Flow domain. The flow region (flow domain) is modeled in Three-Dimensional Computer Aided Design (3D CAD) software and then discretized (meshed) using ICEM. The structured mesh was then exported to a commercial CFD code where, the boundary condition and solver settings for fluid and flow properties, convergence criterion were defined. The numerical simulation was carried out using SIMPLE algorithm for pressure velocity coupling, realizable k epsilon model for modeling turbulence. The realizable k epsilon model is modification to the traditional k epsilon model by giving a benefit of better performance in simulation of planar and round jets (ANSYS Inc, 2013), rotation, recirculation and streamline curvature (Wasserman, 2021). The Pelton turbine jet has streamline curvature in at nozzle exit and is expanding Jet (Bajracharya et al. et al., 2019; Zhang, 2016).
Figure 6: Flow domain. The flow region (flow domain) is modeled in Three-Dimensional Computer Aided Design (3D CAD) software and then discretized (meshed) using ICEM. The structured mesh was then exported to a commercial CFD code where, the boundary condition and solver settings for fluid and flow properties, convergence criterion were defined. The numerical simulation was carried out using SIMPLE algorithm for pressure velocity coupling, realizable k epsilon model for modeling turbulence. The realizable k epsilon model is modification to the traditional k epsilon model by giving a benefit of better performance in simulation of planar and round jets (ANSYS Inc, 2013), rotation, recirculation and streamline curvature (Wasserman, 2021). The Pelton turbine jet has streamline curvature in at nozzle exit and is expanding Jet (Bajracharya et al. et al., 2019; Zhang, 2016).
As the flow simulation results were converged, then 77000 sand particles from were introduced normally from inlet to the flow. In the validated flow model, particles with maximum diameter 2 mm were introduced and nature of its flow along with the jet was studied for three different condition. The particle size distribution of the sand sample used for the study is shown in Fig. 9. Table 1: Summary of solver settings
As the flow simulation results were converged, then 77000 sand particles from were introduced normally from inlet to the flow. In the validated flow model, particles with maximum diameter 2 mm were introduced and nature of its flow along with the jet was studied for three different condition. The particle size distribution of the sand sample used for the study is shown in Fig. 9. Table 1: Summary of solver settings
Figure 7: Boundary and boundary conditions Fig. 6 is the flow domain, the dimensions of the injector are those of a 2 kW model Pelton turbine test rig (Bajracharya et al., 2007) located at Center for Energy Studies, Institute of Engineering. To better capture the viscous layer effects, the fine mesh was used in the needle wall and in the nozzle wall. The axially symmetric nature of the flow domain made the choice of O-grid optimum in this case. Fig. 7 and 8 give the boundary conditions and longitudinal section of the mesh.
Figure 7: Boundary and boundary conditions Fig. 6 is the flow domain, the dimensions of the injector are those of a 2 kW model Pelton turbine test rig (Bajracharya et al., 2007) located at Center for Energy Studies, Institute of Engineering. To better capture the viscous layer effects, the fine mesh was used in the needle wall and in the nozzle wall. The axially symmetric nature of the flow domain made the choice of O-grid optimum in this case. Fig. 7 and 8 give the boundary conditions and longitudinal section of the mesh.
Figure 8: Meshing details
Figure 8: Meshing details
Figure 9: Particle size distribution of sand sample (Rosin Rammler Fitted Curve)
Figure 9: Particle size distribution of sand sample (Rosin Rammler Fitted Curve)
Figure 11: Jet geometry for half open injector (Right image courtesy of Staubli et al. 2004) An ideal jet is supposed to have uniform velocity distribution in each cross section and the jet diameter is constant without any contraction or expansion (Zhang, 2016). Experimental investigations of the jet (Staubli & Hauser, 2004; Zhang & Casey, 2007) reveal that the real jet deviates from this ideal form. The real jet first contracts after it exits from the nozzle and then it expands. The geometry of jet flow obtained also matches with the experimental observation. Fig. 11 shows the jet geometry for half open injector. The jet contraction ahead of the nozzle exit can be seen. This contraction is associated with jet energy loss.
Figure 11: Jet geometry for half open injector (Right image courtesy of Staubli et al. 2004) An ideal jet is supposed to have uniform velocity distribution in each cross section and the jet diameter is constant without any contraction or expansion (Zhang, 2016). Experimental investigations of the jet (Staubli & Hauser, 2004; Zhang & Casey, 2007) reveal that the real jet deviates from this ideal form. The real jet first contracts after it exits from the nozzle and then it expands. The geometry of jet flow obtained also matches with the experimental observation. Fig. 11 shows the jet geometry for half open injector. The jet contraction ahead of the nozzle exit can be seen. This contraction is associated with jet energy loss.
Figure 12: Particle motion for fully open injector
Figure 12: Particle motion for fully open injector
Figure 13: Particle Trajectories for fully open injector
Figure 13: Particle Trajectories for fully open injector
Fig. 14 shows the motion of the sand particles in quarter closed injector. The particles in addition to hitting the needle seat partly hits the needle surface just upstream of the tip. The impingement angle is seen to be between 0 to 20 degrees. The simplified representation of the trajectories is presented in Fig.15. Figure 14: Particle motion for quarter closed injector
Fig. 14 shows the motion of the sand particles in quarter closed injector. The particles in addition to hitting the needle seat partly hits the needle surface just upstream of the tip. The impingement angle is seen to be between 0 to 20 degrees. The simplified representation of the trajectories is presented in Fig.15. Figure 14: Particle motion for quarter closed injector
Figure 15: Simplified particle trajectories for quarter closed injector
Figure 15: Simplified particle trajectories for quarter closed injector
In case the injector is half closed, the particle strikes in region between the needle tip and nozzle exit not uniformly but randomly on a specific region (see Fig.16 and 17). The needle surface-sand particle interaction increases more in comparison to the quarter closed condition. This shows that more erosion can be expected if the turbine is operated on partial load. This supports the findings of Bajracharya et al. (2008) who stated that erosion is directly related to the loading condition of the machine and it is dangerous with regards to erosion to operate the machine in part load. Figure 16: Particle motion for half-closed injector
In case the injector is half closed, the particle strikes in region between the needle tip and nozzle exit not uniformly but randomly on a specific region (see Fig.16 and 17). The needle surface-sand particle interaction increases more in comparison to the quarter closed condition. This shows that more erosion can be expected if the turbine is operated on partial load. This supports the findings of Bajracharya et al. (2008) who stated that erosion is directly related to the loading condition of the machine and it is dangerous with regards to erosion to operate the machine in part load. Figure 16: Particle motion for half-closed injector
Figure 17: Simplified particle trajectories for half-closed injector
Figure 17: Simplified particle trajectories for half-closed injector
3.3 Erosion Table 2: Summary of particle — wall interactions for different cases
3.3 Erosion Table 2: Summary of particle — wall interactions for different cases
Figure 18: Flow velocity and particle motion
Figure 18: Flow velocity and particle motion
Figure 19: Erosion behavior of materials (Hutchings, 1981) Table 2 summarizes the number of particles (among 100 particles) that hit selected surfaces. For fully open injector, the particles hit only the nozzle at exit only. The region is also maximum velocity region (see Fig. 18), these high speed particles when hit the nozzle at the exit, cause mass of nozzle to erode. Among 100 particles, 15 particles hit the nozzle at exit area. The number of particles hitting nozzle is fairly constant for other two cases with slight increase for partially open injectors. For the case of needle, no particles hit the needle for fully open injector while with partial opening, some particles that hit the nozzle and rebound towards needle were hitting the needle before leaving the injector domain. The number of particles hitting the needle has increased with partial opening and for half open injector, 22 particles were found to be hitting the needle. The hitting area was area ahead of nozzle exit. The impact angle of the particle was around 10 to 30 Degrees for region near tip and was greater than 30 Degrees for region farther from the tip. Hence as seen from field setting researches (Neopane et al., 2011; Thapa, 2004) more erosion can be expected at near tip reoion with less erosion upstream of the needle tin.
Figure 19: Erosion behavior of materials (Hutchings, 1981) Table 2 summarizes the number of particles (among 100 particles) that hit selected surfaces. For fully open injector, the particles hit only the nozzle at exit only. The region is also maximum velocity region (see Fig. 18), these high speed particles when hit the nozzle at the exit, cause mass of nozzle to erode. Among 100 particles, 15 particles hit the nozzle at exit area. The number of particles hitting nozzle is fairly constant for other two cases with slight increase for partially open injectors. For the case of needle, no particles hit the needle for fully open injector while with partial opening, some particles that hit the nozzle and rebound towards needle were hitting the needle before leaving the injector domain. The number of particles hitting the needle has increased with partial opening and for half open injector, 22 particles were found to be hitting the needle. The hitting area was area ahead of nozzle exit. The impact angle of the particle was around 10 to 30 Degrees for region near tip and was greater than 30 Degrees for region farther from the tip. Hence as seen from field setting researches (Neopane et al., 2011; Thapa, 2004) more erosion can be expected at near tip reoion with less erosion upstream of the needle tin.
Development of Axial Velocity of Jet for Fully Open Injector
Development of Axial Velocity of Jet for Fully Open Injector
Development of Axial Velocity of Jet for Quarter Open Injector At 5mm Ahead of Needle Tip
Development of Axial Velocity of Jet for Quarter Open Injector At 5mm Ahead of Needle Tip
At 20 mm Ahead of Needle Tip At 80 mm Ahead of Needle Tip
At 20 mm Ahead of Needle Tip At 80 mm Ahead of Needle Tip
Development of Axial Velocity of Jet for Half Open Injector
Development of Axial Velocity of Jet for Half Open Injector
At 40 mm Ahead of Needle Tip
At 40 mm Ahead of Needle Tip
At 5mm Ahead of Needle Tip
At 5mm Ahead of Needle Tip
At 20 mm Ahead of Needle Tip At 80 mm Ahead of Needle Tip
At 20 mm Ahead of Needle Tip At 80 mm Ahead of Needle Tip
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MechanicsInjector Nozzle
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