3.5 Coupling procedure
4.1.3 Velocity field inside the motor housing
In the electric motors, the velocity field within the motor has a character of the forced convection which is the effect of the motion of the rotating components. Moreover, the ve-locity field resulted was also affected by the heat transfer between the internal air and solid elements. For this reason, the numerical results concerning the velocity field within the mo-tor are discussed in this section.
In Fig. 4.13, the velocity vector in the rotor vicinity is illustrated. The results presented in this figure are consistent with the study results published in [109]. In the cited paper, the model domain was limited to the air within the motor. Therefore, the numerical mesh in this domain was finer. The moving components within the motor, presented in the cited study, consisted of a smooth rotor without cavities. In addition, the model was based on the settings in which solid part of the rotor was rotated. No slip boundary condition between solid and fluid domain allowed to reach the speed of the rotor by air in the air gap. The same result was achieved in the model presented in this dissertation. Therefore, the velocity vectors depicted in Fig.4.13are the effect of the rotational speed and local rotor diameter.
5.84
Figure 4.13: Velocity vectors inside the motor housing at Operating Point II
The velocity results obtained from the numerical model were validated on the basis of experimental tests conducted during Experimental Campaign I described in Section 2.1.
Therefore, in the numerical model, the obtained data were monitored in locations within the motor that were depicted as LDA1 and LDA2 in already presented Fig.2.3.
Horizontal component of the velocity vector in LDA1 section
At first, a comparison was made between the horizontal component of the velocity vec-tor for the CFD and experimental results in the LDA1 section as shown in Fig. 4.14. The line marked as continuous in red colour presents the numerical results. It is noticeable that the velocity obtained by the model and the measurements is negative in the region near the housing wall. The first value was measured at 0.001 m from the wall. That means the hori-zontal velocity component is directed to the front of the motor in this region. The numerical results show the same tendency but the maximum velocity value in the front motor direction achieved approx. 0.1 m · s−1. According to the experiments, the direction of the horizontal velocity component changes at approximately 1 cm from the wall. The same tendency can be observed in the model results. Moreover, a rapid increase of the horizontal velocity in the direction of the motor front at a distance of approximately 1 cm from the wall can be observed. The experimental results show a sudden decrease in the close shaft vicinity. How-ever, model results show continuous growth ending on the motor shaft where the horizontal velocity component decreased to zero.
0 0.005 0.01 0.015 0.02 0.025
−0.1 0 0.1
close to wall close to shaft, m
Horizontalvelocity,m·s−1 Experiment
CFD
Figure 4.14: Horizontal component of the velocity vector within motor on a height of the shaft axis (LDA1 in Fig.2.3) at Operating Point III
For the higher rotational speed of 2500 rpm defined at Operating Point IV, a more
de-tailed analysis was conducted. The results obtained from the presented numerical model covering all motor components are represented by a red line in Fig. 4.15. In this figure, the experimental results are presented using the black line. Due to overestimation of the veloc-ity in the region close to the shaft, an additional model was created which was geometrically reduced to the air zone at the back part of the motor. Therefore, the velocity field validation was also performed using the reduced model. For this model, three numerical meshes with the element range between 0.7 and 3 million were tested during the calculation process. In that model, the temperature profiles were implemented for all the investigated loads from the full model described in the previous sections. Therefore, in Fig. 4.15, the line marked as dotted in blue colour represents the results obtained from the reduced model at the loca-tion of the LDA1 line. In addiloca-tion, the second line that represents the velocity in the secloca-tion moved by 5 mm to the front of the motor is depicted in this figure and was expressed by green dotted line.
A comparison of the two positions was used to visualise the velocity field in the analysed region. The velocity obtained by the reduced model and during the experiments is negative in the region near the wall, similarly as in the full model. The first value was measured at 0.001 m from the wall. That means that the horizontal velocity component was directed to the front of the motor in this region. According to the experimental test, the direction of the horizontal velocity component was changed at approximately 1 cm from the wall. This tendency was similar for all the presented numerical and experimental results. Moreover, a rapid increase of the horizontal velocity in the direction of the motor front at a distance of approximately 1 cm from the wall was observed. The experimental results showed a sudden decrease in the direct shaft vicinity. At this location, the CFD results from the described models revealed the changes between the three presented lines. The second line (green) moved by 5 mm to the front of the motor shows better agreement with the measured values than the first line (blue) recorded in the middle of the back part of the motor. However, the results obtained from the full numerical model present tendency of the rapid velocity increase just before the shaft vicinity.
In Fig. 4.16, the results of the horizontal component of the velocity vector from the re-duced numerical model are compared with the conducted experiment at Operating Point V.
As in the previous discussion, the red line represents the results obtained from the reduced model in the LDA1 test section. Additionally, in this figure, the second line (green) represents the velocity in the section moved by 5 mm to the front of the motor. A similar tendency can be observed as in Operating Point IV. However, for the higher speed occurring at Operating Point V, the maximum and minimum values of the CFD and experimental results are more
0 0.005 0.01 0.015 0.02 0.025 0.03 0
0.2 0.4
close to wall close to shaft, m
Horizontalvelocity,m·s−1 Experiment
CFD reduced: 1st line CFD reduced: 2nd line CFD
Figure 4.15: Horizontal component of the velocity vector within motor on a height of the shaft axis (LDA1 in Fig.2.3) at Operating Point IV
intensive.
0 0.01 0.02 0.03
−0.1 0 0.1 0.2 0.3
close to wall close to shaft, m
Horizontalvelocity,m·s−1 Experiment
CFD reduced: 1st line CFD reduced: 2nd line
Figure 4.16: Horizontal component of the velocity vector within motor on a height of the shaft axis (LDA1 in Fig.2.3) at Operating Point V
Vertical component of the velocity vector in LDA1 section
In the following results, the comparison was made between the vertical component of the velocity vector for the CFD and experimental results in the LDA1 section as shown in Fig.
2.3. In Fig. 4.17, the vertical component of velocity on the height of the shaft axis (LDA1) is compared between the numerical and the experiment results at Operating Point III. In this figure, the results of the numerical model that covers all the motor components are pre-sented. In LDA1 section for the experimental and numerical results, the vertical velocity in-creases slightly from the housing wall vicinity to the distance of 0.02 m. In the distance, more than 0.022 m, the values derived from the CFD model increased rapidly to achieve the trans-lational velocity of the shaft which is of approx. 1 m · s−1. The same tendency is observed during the experimental tests in the last 3 measured points. This measurement allowed for recording the higher velocities in the shaft vicinity which are expected in this location. The values in the measured range are similar between the CFD and experimental results. More-over, for the vertical component, the full and reduced models showed the same tendency.
0.000 0.005 0.010 0.015 0.020 0.025 0
0.2 0.4 0.6 0.8 1 1.2
close to wall close to shaft, m
Verticalvelocity,m·s−1
Experiment CFD
Figure 4.17: Vertical component of the velocity vector within the motor on a height of the shaft axis (LDA1 in Fig.2.3) at Operating Point III
In Fig. 4.18, the vertical component of the velocity vector on the height of the shaft axis (LDA1) is compared between results obtained from the experiment and the numerical model at Operating Point IV. The numerical results are presented for both full and reduced model as described in the previous paragraphs. In the LDA1 section, the experimentally recorded vertical velocity component increases slightly from the wall vicinity to the shaft direction approaching the end of the recorded range. In the distance behind recorded range from
measurements, i.e., more than 0.022 m, the values derived from the CFD model increased rapidly to achieve the translational velocity of the shaft. This value from CFD model, in the end, achieves the translational velocity of approx. 1.8 m · s−1. However, the velocity range in Fig.4.18was limited to 1 m · s−1to show the obtained results more clearly. The values in the measured range are similar between the experimental and CFD results. The lack of velocity increase in the experiment series, in the shaft vicinity, can be caused by two reasons. In the direct shaft vicinity, the smoke seeding could be more dispersed resulting in the lower quality of the LDA tests. Moreover, the maximum velocity value could occur in the space between the measured points with a one-millimetre distance. In Fig. 4.18, the two lines obtained from the CFD model were also presented. The second line (green) moved by 5 mm to the front of the motor shows a similar agreement with the measured values as the first line (red) recorded in the middle of the back part of the motor. The difference between the two lines is negligible for the vertical velocity component along the height of the shaft axis.
0.000 0.005 0.010 0.015 0.020 0.025 0.030 0
close to wall close to shaft, m
Verticalvelocity,m·s−1
Experiment CFD CFD reduced
Figure 4.18: Vertical component of the velocity vector within the motor on a height of the shaft axis (LDA1 in Fig.2.3) at Operating Point IV
In Fig.4.19, the last group of the results of the vertical component on the shaft axis height is discussed. In this figure, the results from the reduced model working at Operating Point V are presented. The same tendency of the experimental and numerical velocity values are obtained as in the previous case, e.g. Operating Point IV. However, the values of the pre-sented velocity are proportionally higher, due to the shaft translational velocity of approx.
2.56 m · s−1. Both presented lines that originate from the numerical model represent similar behaviour, despite the second line (green) was moved by 5 mm to the front of the motor from the LDA1 position. Similarly, as in the previous case, the experimental values show very low values in the shaft vicinity, while the results of the model almost achieved the values of the
shaft rotational speed.
0.000 0.005 0.010 0.015 0.020 0.025 0.030 0
0.2 0.4 0.6 0.8 1
close to wall close to shaft, m
Verticalvelocity,m·s−1
Experiment CFD CFD reduced
Figure 4.19: Vertical component of the velocity vector within the motor on a height of the shaft axis (LDA1 in Fig.2.3) at Operating Point V
Horizontal component of the velocity vector in LDA2 section
The following results compared the experimental recordings with the model results in the section above the shaft. Therefore, the presented results are shown in the LDA2 position depicted in Fig.2.3.
The first results were compared at Operating Point III between the results obtained from the full CFD model and the experimental tests. In Fig.4.20, the values recorded in the exper-iment and resulting from the model are negative from the housing wall to the distance from this wall of 0.01 m. In this range, the model results show higher values directed to the motor front. The horizontal velocity component changed its direction in the distance of approx.
0.01 m from the housing wall for both the experimental and numerical results. In the further distance, the velocity increase is observed and then it rapidly decreases in the shaft vicinity.
In Fig. 4.21, the horizontal component of the velocity vector is presented at Operating Point IV on the basis of the experiment and the results similarly as in the previous paragraph for the reduced numerical model. The red line represents the LDA2 position, while the green one shows the results from the section moved by 5 mm to motor front. A similar tendency can be observed in the region close to the housing wall as in the previously described op-erating point. The horizontal velocity shows negative values to the distance of 0.01 m from
0.00 0.01 0.02 0.03
−0.10
−0.05 0.00 0.05 0.10
close to wall close to shaft, m
Horizontalvelocity,m·s−1 Experiment
CFD
Figure 4.20: Horizontal component of the velocity vector within the motor on a height above the shaft axis (LDA2 in Fig.2.3) at Operating Point III
the wall. However, the difference when compared to Operating Point III is that the veloc-ity increased to the direct shaft vicinveloc-ity. Comparing the results from the LDA2 section to the horizontal velocity component conducted in the LDA1 section, the tendency is differ-ent because the green dotted line show worse consistency than the blue one. In this case, the second line behind the distance of 0.02 m from the wall began decreasing and reached approximately 0 m · s−1in the shaft vicinity.
0.00 0.01 0.02 0.03
−0.1 0 0.1
close to wall close to shaft, m
Horizontalvelocity,m·s−1 Experiment
CFD reduced 1st line CFD reduced 2nd line
Figure 4.21: Horizontal component of the velocity vector within the motor on a height above the shaft axis (LDA2 in Fig.2.3) at Operating Point IV
In Fig. 4.22, the horizontal component of the velocity vector is presented at Operating
Point V. Similarly to the previous figure, the CFD results were presented for the two mapped lines. In the figure, the CFD results are consistent with the measured values for the entire range of the investigated section. At first, near the wall, the horizontal velocity was directed in front of the motor with negative values. The maximum value in this direction reached approx. 0.1 m · s−1. Similarly to the previously described section, the horizontal velocity changed its direction at a distance of approx. 0.01 m towards the back of the motor (positive values). From this point, the measured values began to gradually increase. The CFD re-sults of the horizontal velocity component reasonably reflected the experiment in the LDA2 section to a distance of 0.02 m from the wall. The CFD results on the first line increased according to the measured values.
0.00 0.01 0.02 0.03
−0.1 0 0.1 0.2
close to wall close to shaft, m
Horizontalvelocity,m·s−1 Experiment
CFD reduced 1st line CFD reduced 2nd line
Figure 4.22: Horizontal component of the velocity vector within the motor on a height above the shaft axis (LDA2 in Fig.2.3) at Operating Point V
Vertical component of the velocity vector in LDA2 section
The last group of the velocity results that were recorded inside the motor is the vertical component of the velocity vector in the LDA2 section located above the motor shaft as shown in Fig.2.3.
The results obtained at the motor working at Operating Point III on the basis of the full numerical model and the experimental tests are shown in Fig.4.23. In this figure, the vertical velocity component starting from 0 m · s−1at the housing wall to the values two times higher than those reported in the experimental tests can be observed. The slight velocity reduction
is reported at the distance of 0.025 m from the housing wall and moving to the shaft the verti-cal component of the velocity vector increases to the level of 0.2 m · s−1to finally decrease to zero in the shaft vicinity. That local maximum was not confirmed by the experimental data.
0.00 0.01 0.02 0.03
0.00 0.05 0.10 0.15 0.20 0.25
close to wall close to shaft, m
Verticalvelocity,m·s−1
Experiment CFD
Figure 4.23: Vertical component of the velocity vector within the motor on a height above the shaft axis (LDA2 in Fig.2.3) at Operating Point III
At Operating Point IV, the behaviour of the velocity vertical component is similar as in the previous Operating Point. In Fig. 4.24, the blue dotted line was used to present the results in the LDA2 section on the basis of the reduced numerical model. Nevertheless, the velocity values from the CFD results are approximately two times greater than those obtained from the experiments up to a distance of 0.02 m from the wall. Then this difference decreased but still, it was significant. In Fig. 4.24, the second line (green) representing the LDA2 section moved to the motor front by 5 mm, shows slightly lower values than those from the first line.
Simultaneously, these values are more similar to the experimental data. However, a similar tendency can be noted in these two lines.
In Fig. 4.25, the vertical component of the velocity vector on the line above the shaft (LDA2) is presented at Operating Point V. In this conditions, the measured velocity values increased from 0 m · s−1in the vicinity of the wall to approx. 0.2 m · s−1at a distance of 0.02 m from the wall. The CFD results showed an increasing tendency in the same section, but the values are approximately two times greater than the measured values. At distances further than 0.02 m from the wall, the velocity increased again achieving approximately 0.25 m · s−1. In this region, the velocity from the experiment and the model are similar. In the vicinity close to the shaft, the vertical velocity component significantly decreased in the CFD results that was consistent with the test results.
0.00 0.01 0.02 0.03 0
0.1 0.2 0.3 0.4
close to wall close to shaft, m
Verticalvelocity,m·s−1
Experiment CFD reduced 1st line CFD reduced 2nd line
Figure 4.24: Vertical component of the velocity vector within the motor on a height above the shaft axis (LDA2 in Fig.2.3) at Operating Point IV
0.00 0.01 0.02 0.03
−0.1 0 0.1 0.2 0.3 0.4
close to wall close to shaft, m
Verticalvelocity,m·s−1
Experiment CFD reduced 1st line CFD reduced 2nd line
Figure 4.25: Vertical component of the velocity vector within the motor on a height above the shaft axis (LDA2 in Fig.2.3) at Operating Point V