This paper compares the results of six calculation methods on the aerodynamic characteristics of the X-Rotor, which has a special shape, and in particular examines the influence of the vertical induced velocity caused by the rotor shape. The outline and results of each model are well summarized and described, and it is considered a useful paper that other researchers can refer to.

However, the reviewer presents some questions as follows:

(1) Section 2.1.6

PFLOW simulation includes the secondary rotors. The size of the secondary rotor should be stated in the paper. In addition, it is better that information, such as the rotational speed of the secondary rotor blades and its thrust force (drag force) in the PFLOW calculation, is described in the paper. The reviewer suspects that the aerodynamic loss of the entire X-Rotor may be quite large, because the secondary rotors generate power and the propeller blades generate large drag.

(2) Section 3.1.1

line 189-190

In DMS, when the pitch angle β becomes negative, the Cp increases unlike other models. The authors think that this can be attributed to the assumption of DMS in which the downstream actuator is placed in the completely expanded (decelerated) flow field of the upwind actuator. The reviewer would like to request the authors to show and compare the flow field in the mid of the rotor between different models.  The velocity distribution of DMS which will be compared can be the completely expanded flow speed after the upwind half.

(3) Section 3.1.1

line 197-199

The authors attribute the reason, why the Cp is smaller in URANS compared to the vortex method, to the blockage due to the small size of the calculation area. However, if the distance of rotor from the inlet is small, the Cp generally increases compared to the calculation with sufficiently large distance.

Although the authors mentioned it again in lines 338-340 of Chap 4 "Conclusions", it does not seem to be reasonable to explain that the Cp of URANS is smaller than that of the vortex method because the calculation area is small.

Appearance etc.

Appendix C

line 371-372

Correct the way you write the sentence "Resolution, deltax, ....... 7.1942×10-6", please.

line 373

"2.1 Grid ------ comparison" 

Check please.

line 375

4.76×10-3 →　4.76×10^-3 　or  4.76E-3

line 377

18995 CPU hours per revolution  →　18995 CPU hours (about 40 days) per revolution (？)

Revise please.

The paper compares aerodynamic models on the singularly shaped X-Rotor, considering different fixed pitch offsets. The methodology is clear and results are useful for further research in VAWTs.

Questions and comments:

line 149: Table 2 includes twist, which is not mentioned or discussed.

line 156: 72 azimuthal discretizations per rotation big; QBlade can be sensitive to this. Did the authors consider other discretizations?

line 227: PFLOW lower blade forces are affected by the tower blade interaction but also by the secondary rotors included. There is no mention of this.