Time Domain Modeling of Propeller Forces due to Ventilation in Static and Dynamic Conditions
Round 1
Reviewer 1 Report
This is quite interesting paper and useful for readers.
Following are not so important questions which will affect the story, but I would like to ask the author to reply kindly.
(1) As for eq.(9), βT should be replaced by βcv or should be removed?
(2) I wonder whether βT for Q is not zero when βT for T is zero in Fig.1 because the drag component is not zero when the lift is zero.
(3) What is a difference of definition among thrust loss βT, Kt/Ktu and thrust ratio Kt/Kt0 ? Please use the same definition and letters if the meanings are the same.
These characters appear in the Fig.19 and Fig.20 etc..
In seems that the data shown in Fig.19 is thrust coefficient itself, and not βT.
Please confirm the title of vertical axis.
Author Response
Please find the reply to the reviewer in the attatchement
Best Regards
Anna Maria Kozlowska
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Summary: The paper presents the results of a method developed to estimate propeller forces and losses in different operating conditions, considering ventilation effects. In particular, the effect of blade force decay due to ventilation is taken into account by means of lift coefficient reduction. The results of the proposed method are compared both with experimental data and CFD results in order to validate the model accuracy and to analyze the limits of the method.
General comments: The Authors have proposed an interesting method in order to face the lack of simple yet reliable methods able to predict the blade force reduction in ventilation conditions for propellers. Moreover, such efforts have been made in order to also take into account complex phenomenon, such as hysteresis, in time-varying conditions. However, I feel like there are some parts of the paper that should be written better. Please see in the following some detailed comments:
1) Page 2 - 2.2 Submerged, vortex ventilation, line 8
“for fully ventilated propellers assuming that the suction side of the propeller blade is fully ventilated and the pressure on the pressure side of the propeller blade section is equal to the static pressure”
In my opinion, static pressure, static pressure always operates on both sides of the blade (pressure and suction sides) for all operating conditions, while is the static pressure that assumes particular values.
2) Page 6
“The relation presented... model presented in Kozlowska et.al. [11].”
Please better highlight the differences between 2016 and 2018 versions
3) Page 8 – Figure 3
If possible, please indicate experiments with dots and numerical results with lines. This help to evaluate the experimental sampling rate.
4) Page 8 – Figure 4 and comments
Even if the 2018 version is better for thrust loss magnitude, the temporal extension of the perturbation is better predicted by 2016 version. In addition, if the thrust loss is evaluated by a integral point of view, both solutions are quite different from experiments (2016 overestimates, while 2018 underestimates). Please comment.
5) Page 8 – comments on Figure 5
Please highlight the differences between case presented in Fig 4 and that presented in Fig. 5. Moreover, it seems that for 2018 model the value of beta_t is equal to 1 for all the simulated time. Probably the values are close to unit, even if locally different from 1. Please comment.
6) Page 11 – Caption of Table 2
Please add the comments in caption of the table within the text.
7) Page 11 – Figure 8
The blue line for “go up” behavior can't be seen in the picture. Probably is under the black line. Please try to improve the quality of the Figure or comment.
8) Page 13 – line 10-16 and Figure 11
“During measurements different... hysteresis effect discussed above.”
All this paragraph is quite difficult to be understood. From Figure 11, it is quite difficult to understand how the experimental results could be employed for CFD and proposed method validation.
9) Page 13 – Figure 12
The behavior computed by proposed method seems to be perfectly cyclic on the 360 degrees of the revolution, while the CFD results present a “non-symmetric” behavior with respect to the middle of the revolution (180 degrees). Please comment.
10) Page 14 – Figure 14
The results form proposed method seem provide a constant profile of thrust ratio, equal to one, without variations in the cycle. Please comment.
11) Page 15 – Line 1-2
The trends in Figure 16 are different. The experimental results show a peak at around 150 degree, while the maximum value computed by proposed method is at 270 degree. Moreover, the proposed method seems to compute a value equal to zero from 0 to 90 and from 280 to 360 degree. Please comments
12) Page 15 – Lime 3 under Figure 16
“Figure 17 and Figure 18 show good agreement between experimental results and calculations”. This is, in my opinion, not true. The differences between experiments and numerical results are quite evident: the behavior of the coefficient, the position and magnitude of the peak and the integral value that can be obtained by the two curves are very different.
Some other minor concerns:
1) Page 7 – line 1
“The same propeller model (P1374) was used for these experiments, the propeller has a diameter of
250mm, design pitch ratio of 1.1 and expanded area ratio of 0.595.”
Substitute the comma with ; or with :
2) Page 9 – Line 1 after eq 11
“One, which corresponds with time, which is required for ventilation to establish and the other, which correspond with time, which is desired for ventilation to disappear.”Please substitute correspond with corresponds
3) Page 17 – Conclusions
The sentence “The hysteresis effect is caused by the fact that it takes a while for ventilation of a submerged propeller to be established, so in a situation with decreasing submergence or increasing propeller loading, there is less thrust loss than for the same condition in static operation, while when ventilation disappears, it takes time for thrust to build up, due to what is called Wagner effect, so then thrust loss is larger than the corresponding static operation.” is, in my opinion, too long. Please try to rewrite in more understandable way.
Author Response
Please find the reply to the reviewer in the attatchement
Best Regards
Ann Maria Kozlowska
Author Response File: Author Response.pdf
