Numerical Prediction of the Aerodynamics and Acoustics of a Tip Leakage Flow Using Large-Eddy Simulation^†

Round 1

Reviewer 1 Report

Mandatory Request Changes:Mandatory Changes: Requested changes which are essential for the understanding and completeness of the paper. Paper of author(s) who have not complied with these requests may be rejected.:
no

Recommended Requested Changes:Recommended Changes: Changes will improve the quality of the paper. Authors are strongly encouraged to comply with these requests.:
In this article, both RANS and wall-modeled LES have been performed on blade tip flows in a simplified geometry. The simulation has been compared with experimental measurements at incoming velocity profile, airfoil pressure distribution, tip leakage flows and tip-region pressure fluctuations. The detachment of tip leakage flow is identified as the origin of the peak frequency in the tip pressure spectra. The simulation is of good quality, but the analysis is a bit preliminary for the moment. I recommend it to be accepted for conference presentation and suggest more analysis on unsteady characteristics of tip leakage flows and its relation to noise generation when considered for journal publication.
There are some specific comments list below:
(1) P4, “the inlet is one chord upstream” Is it enough to avoid numerical reflection?
(2) wall model is used in the simulation, it might not be capable of predicting separated flows, especially in tip region.
(3) P4, what methods are used to generate inlet turbulence for LES? What is the turbulence intensity?
(4) Figure 4, why LES is higher than EXP near the tip? Is it because the flow is separated and wall model cannot cope with it?
(5) Figure 5, (e) and (f), why the simulation of axial velocity is so far away from PIV measurement? What physical process is missing in the simulation for both LES and RANS? Is it also due to the wall model?
(6) Figure 6, normally, LES predicted spectra are cut off at high frequencies, however, this result shows the opposite trend – higher than EXP spectra?

Author Response

Please kindly find the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

Mandatory Request Changes:Mandatory Changes: Requested changes which are essential for the understanding and completeness of the paper. Paper of author(s) who have not complied with these requests may be rejected.:
none

Recommended Requested Changes:Recommended Changes: Changes will improve the quality of the paper. Authors are strongly encouraged to comply with these requests.:
pg 2 change "...often used to compute the mean flow-field and fed analytical modelling..." to "...feed..."
pg 4 change "...cells is about
28x106, splitted into 622 structured..." to "...split..."

Author Response

Please kindly find the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Mandatory Request Changes:Mandatory Changes: Requested changes which are essential for the understanding and completeness of the paper. Paper of author(s) who have not complied with these requests may be rejected.:
The information in Figure 4b and associated caption on z/s should be reconciled.

Recommended Requested Changes:Recommended Changes: Changes will improve the quality of the paper. Authors are strongly encouraged to comply with these requests.:
The paper is a nice comparison between CFD based on statistical turbulence modelling (RANS) and turbulent scales resolving LES with measurements based on PIV of the mean flow field of an isolated airfoil between two horizontal plates and a gap. Furthermore, mean pressures and pressure spectra on the airfoil surface for characterising the blade tip flow are discussed between the simulation results and available measured data.

In the paper, the numerical simulations are highlighted as the main focus. The quality of the work could further be improved by providing more information on the numerics used. This includes in particular more detailed representations of the mesh, such as the distribution of points in the gap and around the airfoil. It would also be helpful to have information on the order in time and space of the LES solver, the expected cut-off frequency, the synthetic turbulence in connection with the degree of turbulence of simulation and measurement. Further information on the formation of the statistics (for example, the length of the initial transients) and the approaches used to evaluate statistical convergence is also helpful information.

In addition, the reviewer is particularly interested in whether the authors have made an angle of attack correction to match the cp data.

Author Response

Please kindly find the attachment.

Author Response File: Author Response.pdf