A conservative immersed boundary method for the multi-physics urban large-eddy simulation model uDALES v2.0

Owens, Sam Oliver; Majumdar, Dipanjan; Wilson, Christopher Edward; Bartholomew, Paul; van Reeuwijk, Maarten

doi:https://doi.org/10.5194/egusphere-2024-96

Preprints

https://doi.org/10.5194/egusphere-2024-96

Preprints

20 Feb 2024

| 20 Feb 2024

A conservative immersed boundary method for the multi-physics urban large-eddy simulation model uDALES v2.0

Sam Oliver Owens, Dipanjan Majumdar, Christopher Edward Wilson, Paul Bartholomew, and Maarten van Reeuwijk

Abstract. uDALES is an open-source multi-physics microscale urban modelling framework, capable of performing large-eddy simulation (LES) of urban airflow, heat transfer, and pollutant dispersion. We present uDALES v2.0, which has two main new features: 1) an improved parallelisation that prepares the codebase for conducting exascale simulations; and 2) a conservative immersed boundary method (IBM) suitable for an urban surface that does not need to be aligned with the underlying Cartesian grid. The urban geometry and local topography are incorporated via a triangulated surface with a resolution that is independent of the fluid grid. The IBM developed here includes the use of wall functions to apply surface fluxes, and the exchange of heat and moisture between the surface and the air is conservative by construction. We perform a number of validation simulations, ranging from neutral, coupled internal-external flows and non-neutral cases. Good agreement is observed, both in cases in which the buildings are aligned with the Cartesian grid and when they are at an angle. We introduce a validation case specifically for urban applications, for which we show that supporting non grid-aligned geometries is crucial when solving surface energy balances, with errors of up to 20 % associated with using a previous version of uDALES.

Received: 11 Jan 2024 – Discussion started: 20 Feb 2024

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Sam Oliver Owens, Dipanjan Majumdar, Christopher Edward Wilson, Paul Bartholomew, and Maarten van Reeuwijk

Status: closed

RC1:
'Comment on egusphere-2024-96', Anonymous Referee #1, 30 Mar 2024
This paper presents enough materials to describe the upgraded key features from uDALES v1.0 to uDALES v2.0 (LES), as well as the crucial technique details. Four cases were tested and validated against the data in the literature, showing the success of the upgrading. I am very pleased to see that the authors have published the uDALES v2.0 codebase and user manual for open access.
The MS is concise and is well prepared. I would recommend ‘accept’ for publication, subject to addressing some minor comments below:
Lns 8-9. Please rephrase this sentence ‘Good agreement …’

2, in the convection term u_i to change to u_j. Give a bit more details about K_h (it should be SGS eddy diffusivity).

Ln 112, change ‘transported’ to ‘convected’.

5, define RH, q_{sat}

Lns 142-144. “Note that the surface energy balance is generally evolved using a larger timestep than the LES, therefore these fluxes are time averaged”. This is not clear enough. These fluxes are constant during the LES, or vary slowly in a quasi-steady manner?

Section 3 title ‘Improvements’ to change to ‘Upgraded key features from uDALES v1.0 to v2.0

3.2. As in the inlet-outlet direction (streamwise), only the Neumann BC can be used. Therefore, the constant pressure boundary condition cannot be used. Given all boundary conditions for pressure are Neumann, any specific treatment is given to settle down a unique solution?

Ln 228. Non-slip boundary condition means non-zero shear, which is wall-normal momentum flux. Please comment.

Lns 245-246. Please describe a bit more of the interpolation here, is it a 2^nd-order accuracy linear interpolation?

Lns 335-338. The ‘real’ turbulence generated by the driver simulations using periodic lateral boundary conditions is governed by the upper and lower boundaries, which are just a simplified condition (but not 100% ‘real’). Please comment.

Ln 374. ‘These differences are most likely caused by differences in the inflow conditions above z/hm = 5 (Fig. 8c)’. The upper boundary conditions in the LES might be one more reason to cause the discrepancy? Please comment.

Section 4.2. Please give the dimensions of the LES domain in the text, although they are shown in Fig. 9.

Section 4.3. The Ri number is kept the same as in Richards et al (2006) and Boppana et al (2013), whereas the Reynolds number is increased by 100 times (or kept the same as Richards et al (2006))? If not, please comment on this.

Section 4.4. Please give the Ri number in the current problem, with a discussion on the capability of uDALES for larger Ri flows.
Citation: https://doi.org/10.5194/egusphere-2024-96-RC1
- AC1:
  'Reply on RC1', Sam O. Owens, 01 May 2024
  
  1. Done - changed to 'We observe good agreement...'
  2. We prefer to use the usual form for advection, i.e. the first velocity component (u_j) is advecting and the second is being advected (u_i). Also, we have added an explanation that K_h is (like K_m) calculated using the Vreman subgrid model.
  3. We propose changing to 'advected', as 'convected' has connotations of vertical motion/heat transfer.
  4. Clarification needed - these are defined in lines 126-127. If the reviewer means we should give formulae for RH and q_sat, we would argue that this is not necessary as they are commonplace, and the aim is to keep the form of the wall functions general (as they are given fully in the referenced uDALES v1 paper).
  5. Changed to 'Note that the turbulent fluxes (H and E) are calculated at every LES timestep, but the surface energy balance is generally evolved using a larger timestep than the LES. The fluxes used to solve for the facet temperatures are therefore the time-average of the fluxes at LES timesteps.'
  6. Done.
  7. The boundary conditions for the Poisson equation are given in Appendix A. In summary: to make the problem well-posed, a Dirichlet condition is used for the zero mode (plane-averaged pressure) at the top.
  8. We thank the reviewer for this point, which was indeed slightly ambiguous in our original phrasing. We do initially impose a free-slip (zero flux) boundary condition by negating any diffusion, and then add shear stress according to the wall function (thus making it no slip). This is hopefully explained clearly later in the section. We have changed this line to ‘uDALES assumes the geometry is non-porous and stationary, which are modelled using no-slip and no-penetration boundary conditions, with the only flux of momentum and scalars across boundaries given by wall functions.'
  9. We don't actually do this interpolation, so we argue further detail is not necessary.
  10. We use 'real' to contrast with synthetic turbulence generation methods - the flow is consistent with the Navier-Stokes equations. The flow is indeed also influenced by the boundary conditions; the bottom boundary condition is of course entirely crucial in determining the flow, and the top boundary condition is not real but its influence tends to be limited and it does not influence the flow near the surface (which is where the focus is). In the text we can perhaps rephrase to 'the turbulence develops naturally'?
  11. Changed to 'These differences are most likely for the same reasons discussed in Xie et. al., namely that the experimental and numerical studies each use a different domain height.
  12. Done - added on line 386.
  13. The Reynolds number for urban flows is typically sufficiently large for the viscous stresses to be negligible compared to the turbulent stresses and pressure, i.e. the flow is essentially independent of Re. This means we can change the geometry scale while keeping flow velocity constant (and thus changing Re) and obtain similar results, as in Sect. 4.1. However, the Richardson number is a measure of the relative strength of buoyancy to the mean kinetic energy of the flow, and this ratio needs to stay the same otherwise the character of the flow will change. We can add an explanation along these lines to the text if the reviewer thinks it would benefit from it.
  14. Clarification needed, as the facet temperature varies - the maximum Richardson number perhaps? With discussion stating that this larger than in Sect. 4.3?
  
  Citation: https://doi.org/10.5194/egusphere-2024-96-AC1
  - RC4: 'Reply on AC1', Anonymous Referee #1, 09 May 2024
    
    I am happy with most of the replies. Some followup comments for the authors to consider,
    4. ok. I might have missed the text above the equation 5.
    10. I suggest "They typically use periodic inlet-outlet boundary conditions, and their advantage is that the technique is simpler to implement requiring less prescribed information, as opposed to the more sophasticated methods, such as the synthetic turbulence generation (e.g. Xie and Castro, 2008)."
    13. Yes, it would be good to include this explanation in the revised MS.
    14. To be consistent with Sect. 4.3, use the facet-average temperature to estimate the Ri number please.
    
    Citation: https://doi.org/10.5194/egusphere-2024-96-RC4
    
    AC2: 'Reply on RC4', Sam O. Owens, 24 May 2024
    
    Given the reviewer’s suggestion, we suggest “They typically use periodic boundary conditions, and their advantage is that the turbulence develops naturally, as opposed to the common alternative approach of quantities being prescribed (on the inlet) and turbulence being generated synthetically (e.g. Xie and Castro, 2008). The precursor technique therefore can be simpler to implement as it requires less prior information, though given the flow is strongly determined by the bottom boundary condition, trial and error is often required to obtain the desired turbulence statistics.”
    
    Added the explanation text to Ln 425.
    
    We suggest adding “The temperature difference between the surface of the leeward face and background air temperature is approximately 16 times higher than in Sect. 4.3, thus yielding Ri = -10. This indicates that buoyancy is more significant for this case.”
    
    Citation: https://doi.org/10.5194/egusphere-2024-96-AC2
- AC7: 'Reply on RC1', Sam O. Owens, 30 May 2024
  
  After making changes to the manuscript having received further reviews, we have decided to amend our responses to the following points:
  6. Changed to 'Upgraded features', as we thought the reviewer's suggestion too verbose.
  10. Changed to "They typically use periodic boundary conditions, and their advantage is that all spatial and temporal statistics of the eddies (e.g. two-point correlations) are representative of real turbulence provided the precursor simulation has an appropriate aspect ratio domain. This is in contrast to the common alternative approach of quantities being prescribed (on the inlet) and turbulence being generated synthetically (Xie et al. 2008). The precursor technique can be simpler to implement as it requires less prior information, though given the flow is strongly determined by the bottom boundary condition, trial and error with respect to the geometry is often required to obtain the desired turbulence statistics."
  Also, we apologise for any confusion caused by mis-numbering the points on AC2 (https://doi.org/10.5194/egusphere-2024-96-AC2).
  
  Citation: https://doi.org/10.5194/egusphere-2024-96-AC7
RC2:
'Comment on egusphere-2024-96', Anonymous Referee #2, 09 Apr 2024

I found the presentation to be clear, and the topic is definitely appropriate. I am not qualified to review the technical aspects of the manuscript.

Citation: https://doi.org/10.5194/egusphere-2024-96-RC2
- AC6: 'Reply on RC2', Sam O. Owens, 30 May 2024
  
  We thank the reviewer for this comment.
  
  Citation: https://doi.org/10.5194/egusphere-2024-96-AC6
RC3:
'Comment on egusphere-2024-96', Anonymous Referee #3, 09 May 2024

see attached report

Citation: https://doi.org/10.5194/egusphere-2024-96-RC3
- AC5: 'Reply on RC3', Sam O. Owens, 30 May 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-96/egusphere-2024-96-AC5-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-96-AC5
RC5:
'Comment on egusphere-2024-96', Anonymous Referee #4, 13 May 2024

Review of " A conservative immersed boundary method for the multi-physics urban large-eddy simulation model uDALES v2.0 "
This study shows result from uDALES v2.0. model which is an upgraded version uDALES v1.0, and compared results with the previous version of uDALES v2.0. and existing literatures. The upgraded version (i.e., uDALES v2.0.) results are consistent with the previous version (i.e., uDALES v1.0) and literatures, and have flexibility to study larger urban areas and run longer simulations. I found this manuscript well written and explain, although, I am not much expert on the technical aspects of the manuscript. I believe this manuscript is suitable for publication in GMD but I have few minor comments that I think would improve the manuscript:
I noticed in the tile that author refers to uDALES v2.0. as a model, whereas in the abstract and rest of the manuscript, author refers to uDALES v2.0 as a framework, which is a bit confusing to me. Therefore, I would suggest stick with one of them to be consistent.
In line 13, it is not clear to me what trend author is referring there.
Line 36-39, I would suggest splitting the sentence, as it is a very long one to follow what information author wants to convey.

Citation: https://doi.org/10.5194/egusphere-2024-96-RC5
- AC3: 'Reply on RC5', Sam O. Owens, 27 May 2024
  
  We thank the reviewer for these comments, and accept the suggested changes:
  
  We have changed 'framework' to 'model' throughout the text.
  
  We have removed 'If current trends continue' on Ln 13, as it is not in fact necessary to the point being made.
  
  We also agree that Lns 36-39 contain unnecessary detail, and have changed the sentence to: "Examples include ENVI-met (Huttner, 2012), SOLENE-Microclimate  (Musy et al., 2015, 2021), urbanMicroclimateFoam (Kubilay et al., 2018), and the model described in Wong et al. (2021)"
  
  Citation: https://doi.org/10.5194/egusphere-2024-96-AC3
RC6:
'Comment on egusphere-2024-96', Anonymous Referee #5, 17 May 2024

General Comments
In the present study , the authors have taken advantage of the existing knowledge to produce a new version (v2.0) of the uDALES code, demonstrating in addition the positive impact of the changes on prediction capabilities.
The effort here is to present the improvements on uDALES 1,0 to become uDALES 2.0. Therefore common descriptions are better to be limited and give more emphasis in the differences.
It is assumed that each application selected serves a specific objective. It is good this specific objective to be described and at the end of the specific exercise, conclusions need to be drawn in relation tothis objective. A generic objective is to compare results of uDALES v2.0 and uDALES v1.0 and commenting on the differences and their causes. Please make sure that those principles are kept to a large degree, for all applications presented.
It is most probable that some limitations still persist in the v2.0 version. It would be helpful, in a separate chapter, such limitations are discussed including the way forward.
Specific Comments
Lines 41- 43 “RANS only resolves the mean flow, and entirely relies on turbulence modelling to incorporate the effect of fluctuating components. As a result, RANS often fails to accurately reproduce transient flow features and quantities such as turbulent kinetic energy (van Hooff et al., 2017).” . It is not evident that the RANS characteristics prevent them to reproduce transient flow features. Do you mean unsteady flow features ? . Concerning turbulent kinetic energy predictions with RANS Models probab;y there are models that claim they can do this. See for example : Bartzis, J,G , Boundary-Layer Meteorology (2005) 116: 445–459 ,DOI 10.1007/s10546-004-7404-y
Lines 45 -46 : “… LES is inherently more accurate than RANS….” . It would be better to say “… LES is expected to be more accurate than RANS”. We should not forget that we have to apply LES correctly and this not always easy for open flows such as the atmospheric boundary layer.
Lines 105-107 : Concerning horizontal grid, it seems that there is a different treatment for x- and y -directions. In real problems this might impose limited degree of freedom in selecting x- and y- directions. In other words is this selection application dependent ?
Lines 110 -113 ; The inlet flow conditions are briefly discussed. The key problem here is how the upwind large eddies are introduced into the computation domain, keeping in mind that any introduced error persists downwind. Please expand.

Citation: https://doi.org/10.5194/egusphere-2024-96-RC6
- AC4: 'Reply on RC6', Sam O. Owens, 30 May 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-96/egusphere-2024-96-AC4-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-96-AC4

Status: closed

RC1:
'Comment on egusphere-2024-96', Anonymous Referee #1, 30 Mar 2024
This paper presents enough materials to describe the upgraded key features from uDALES v1.0 to uDALES v2.0 (LES), as well as the crucial technique details. Four cases were tested and validated against the data in the literature, showing the success of the upgrading. I am very pleased to see that the authors have published the uDALES v2.0 codebase and user manual for open access.
The MS is concise and is well prepared. I would recommend ‘accept’ for publication, subject to addressing some minor comments below:
Lns 8-9. Please rephrase this sentence ‘Good agreement …’

2, in the convection term u_i to change to u_j. Give a bit more details about K_h (it should be SGS eddy diffusivity).

Ln 112, change ‘transported’ to ‘convected’.

5, define RH, q_{sat}

Lns 142-144. “Note that the surface energy balance is generally evolved using a larger timestep than the LES, therefore these fluxes are time averaged”. This is not clear enough. These fluxes are constant during the LES, or vary slowly in a quasi-steady manner?

Section 3 title ‘Improvements’ to change to ‘Upgraded key features from uDALES v1.0 to v2.0

3.2. As in the inlet-outlet direction (streamwise), only the Neumann BC can be used. Therefore, the constant pressure boundary condition cannot be used. Given all boundary conditions for pressure are Neumann, any specific treatment is given to settle down a unique solution?

Ln 228. Non-slip boundary condition means non-zero shear, which is wall-normal momentum flux. Please comment.

Lns 245-246. Please describe a bit more of the interpolation here, is it a 2^nd-order accuracy linear interpolation?

Lns 335-338. The ‘real’ turbulence generated by the driver simulations using periodic lateral boundary conditions is governed by the upper and lower boundaries, which are just a simplified condition (but not 100% ‘real’). Please comment.

Ln 374. ‘These differences are most likely caused by differences in the inflow conditions above z/hm = 5 (Fig. 8c)’. The upper boundary conditions in the LES might be one more reason to cause the discrepancy? Please comment.

Section 4.2. Please give the dimensions of the LES domain in the text, although they are shown in Fig. 9.

Section 4.3. The Ri number is kept the same as in Richards et al (2006) and Boppana et al (2013), whereas the Reynolds number is increased by 100 times (or kept the same as Richards et al (2006))? If not, please comment on this.

Section 4.4. Please give the Ri number in the current problem, with a discussion on the capability of uDALES for larger Ri flows.
Citation: https://doi.org/10.5194/egusphere-2024-96-RC1
- AC1:
  'Reply on RC1', Sam O. Owens, 01 May 2024
  
  1. Done - changed to 'We observe good agreement...'
  2. We prefer to use the usual form for advection, i.e. the first velocity component (u_j) is advecting and the second is being advected (u_i). Also, we have added an explanation that K_h is (like K_m) calculated using the Vreman subgrid model.
  3. We propose changing to 'advected', as 'convected' has connotations of vertical motion/heat transfer.
  4. Clarification needed - these are defined in lines 126-127. If the reviewer means we should give formulae for RH and q_sat, we would argue that this is not necessary as they are commonplace, and the aim is to keep the form of the wall functions general (as they are given fully in the referenced uDALES v1 paper).
  5. Changed to 'Note that the turbulent fluxes (H and E) are calculated at every LES timestep, but the surface energy balance is generally evolved using a larger timestep than the LES. The fluxes used to solve for the facet temperatures are therefore the time-average of the fluxes at LES timesteps.'
  6. Done.
  7. The boundary conditions for the Poisson equation are given in Appendix A. In summary: to make the problem well-posed, a Dirichlet condition is used for the zero mode (plane-averaged pressure) at the top.
  8. We thank the reviewer for this point, which was indeed slightly ambiguous in our original phrasing. We do initially impose a free-slip (zero flux) boundary condition by negating any diffusion, and then add shear stress according to the wall function (thus making it no slip). This is hopefully explained clearly later in the section. We have changed this line to ‘uDALES assumes the geometry is non-porous and stationary, which are modelled using no-slip and no-penetration boundary conditions, with the only flux of momentum and scalars across boundaries given by wall functions.'
  9. We don't actually do this interpolation, so we argue further detail is not necessary.
  10. We use 'real' to contrast with synthetic turbulence generation methods - the flow is consistent with the Navier-Stokes equations. The flow is indeed also influenced by the boundary conditions; the bottom boundary condition is of course entirely crucial in determining the flow, and the top boundary condition is not real but its influence tends to be limited and it does not influence the flow near the surface (which is where the focus is). In the text we can perhaps rephrase to 'the turbulence develops naturally'?
  11. Changed to 'These differences are most likely for the same reasons discussed in Xie et. al., namely that the experimental and numerical studies each use a different domain height.
  12. Done - added on line 386.
  13. The Reynolds number for urban flows is typically sufficiently large for the viscous stresses to be negligible compared to the turbulent stresses and pressure, i.e. the flow is essentially independent of Re. This means we can change the geometry scale while keeping flow velocity constant (and thus changing Re) and obtain similar results, as in Sect. 4.1. However, the Richardson number is a measure of the relative strength of buoyancy to the mean kinetic energy of the flow, and this ratio needs to stay the same otherwise the character of the flow will change. We can add an explanation along these lines to the text if the reviewer thinks it would benefit from it.
  14. Clarification needed, as the facet temperature varies - the maximum Richardson number perhaps? With discussion stating that this larger than in Sect. 4.3?
  
  Citation: https://doi.org/10.5194/egusphere-2024-96-AC1
  - RC4: 'Reply on AC1', Anonymous Referee #1, 09 May 2024
    
    I am happy with most of the replies. Some followup comments for the authors to consider,
    4. ok. I might have missed the text above the equation 5.
    10. I suggest "They typically use periodic inlet-outlet boundary conditions, and their advantage is that the technique is simpler to implement requiring less prescribed information, as opposed to the more sophasticated methods, such as the synthetic turbulence generation (e.g. Xie and Castro, 2008)."
    13. Yes, it would be good to include this explanation in the revised MS.
    14. To be consistent with Sect. 4.3, use the facet-average temperature to estimate the Ri number please.
    
    Citation: https://doi.org/10.5194/egusphere-2024-96-RC4
    
    AC2: 'Reply on RC4', Sam O. Owens, 24 May 2024
    
    Given the reviewer’s suggestion, we suggest “They typically use periodic boundary conditions, and their advantage is that the turbulence develops naturally, as opposed to the common alternative approach of quantities being prescribed (on the inlet) and turbulence being generated synthetically (e.g. Xie and Castro, 2008). The precursor technique therefore can be simpler to implement as it requires less prior information, though given the flow is strongly determined by the bottom boundary condition, trial and error is often required to obtain the desired turbulence statistics.”
    
    Added the explanation text to Ln 425.
    
    We suggest adding “The temperature difference between the surface of the leeward face and background air temperature is approximately 16 times higher than in Sect. 4.3, thus yielding Ri = -10. This indicates that buoyancy is more significant for this case.”
    
    Citation: https://doi.org/10.5194/egusphere-2024-96-AC2
- AC7: 'Reply on RC1', Sam O. Owens, 30 May 2024
  
  After making changes to the manuscript having received further reviews, we have decided to amend our responses to the following points:
  6. Changed to 'Upgraded features', as we thought the reviewer's suggestion too verbose.
  10. Changed to "They typically use periodic boundary conditions, and their advantage is that all spatial and temporal statistics of the eddies (e.g. two-point correlations) are representative of real turbulence provided the precursor simulation has an appropriate aspect ratio domain. This is in contrast to the common alternative approach of quantities being prescribed (on the inlet) and turbulence being generated synthetically (Xie et al. 2008). The precursor technique can be simpler to implement as it requires less prior information, though given the flow is strongly determined by the bottom boundary condition, trial and error with respect to the geometry is often required to obtain the desired turbulence statistics."
  Also, we apologise for any confusion caused by mis-numbering the points on AC2 (https://doi.org/10.5194/egusphere-2024-96-AC2).
  
  Citation: https://doi.org/10.5194/egusphere-2024-96-AC7
RC2:
'Comment on egusphere-2024-96', Anonymous Referee #2, 09 Apr 2024

I found the presentation to be clear, and the topic is definitely appropriate. I am not qualified to review the technical aspects of the manuscript.

Citation: https://doi.org/10.5194/egusphere-2024-96-RC2
- AC6: 'Reply on RC2', Sam O. Owens, 30 May 2024
  
  We thank the reviewer for this comment.
  
  Citation: https://doi.org/10.5194/egusphere-2024-96-AC6
RC3:
'Comment on egusphere-2024-96', Anonymous Referee #3, 09 May 2024

see attached report

Citation: https://doi.org/10.5194/egusphere-2024-96-RC3
- AC5: 'Reply on RC3', Sam O. Owens, 30 May 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-96/egusphere-2024-96-AC5-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-96-AC5
RC5:
'Comment on egusphere-2024-96', Anonymous Referee #4, 13 May 2024

Review of " A conservative immersed boundary method for the multi-physics urban large-eddy simulation model uDALES v2.0 "
This study shows result from uDALES v2.0. model which is an upgraded version uDALES v1.0, and compared results with the previous version of uDALES v2.0. and existing literatures. The upgraded version (i.e., uDALES v2.0.) results are consistent with the previous version (i.e., uDALES v1.0) and literatures, and have flexibility to study larger urban areas and run longer simulations. I found this manuscript well written and explain, although, I am not much expert on the technical aspects of the manuscript. I believe this manuscript is suitable for publication in GMD but I have few minor comments that I think would improve the manuscript:
I noticed in the tile that author refers to uDALES v2.0. as a model, whereas in the abstract and rest of the manuscript, author refers to uDALES v2.0 as a framework, which is a bit confusing to me. Therefore, I would suggest stick with one of them to be consistent.
In line 13, it is not clear to me what trend author is referring there.
Line 36-39, I would suggest splitting the sentence, as it is a very long one to follow what information author wants to convey.

Citation: https://doi.org/10.5194/egusphere-2024-96-RC5
- AC3: 'Reply on RC5', Sam O. Owens, 27 May 2024
  
  We thank the reviewer for these comments, and accept the suggested changes:
  
  We have changed 'framework' to 'model' throughout the text.
  
  We have removed 'If current trends continue' on Ln 13, as it is not in fact necessary to the point being made.
  
  We also agree that Lns 36-39 contain unnecessary detail, and have changed the sentence to: "Examples include ENVI-met (Huttner, 2012), SOLENE-Microclimate  (Musy et al., 2015, 2021), urbanMicroclimateFoam (Kubilay et al., 2018), and the model described in Wong et al. (2021)"
  
  Citation: https://doi.org/10.5194/egusphere-2024-96-AC3
RC6:
'Comment on egusphere-2024-96', Anonymous Referee #5, 17 May 2024

General Comments
In the present study , the authors have taken advantage of the existing knowledge to produce a new version (v2.0) of the uDALES code, demonstrating in addition the positive impact of the changes on prediction capabilities.
The effort here is to present the improvements on uDALES 1,0 to become uDALES 2.0. Therefore common descriptions are better to be limited and give more emphasis in the differences.
It is assumed that each application selected serves a specific objective. It is good this specific objective to be described and at the end of the specific exercise, conclusions need to be drawn in relation tothis objective. A generic objective is to compare results of uDALES v2.0 and uDALES v1.0 and commenting on the differences and their causes. Please make sure that those principles are kept to a large degree, for all applications presented.
It is most probable that some limitations still persist in the v2.0 version. It would be helpful, in a separate chapter, such limitations are discussed including the way forward.
Specific Comments
Lines 41- 43 “RANS only resolves the mean flow, and entirely relies on turbulence modelling to incorporate the effect of fluctuating components. As a result, RANS often fails to accurately reproduce transient flow features and quantities such as turbulent kinetic energy (van Hooff et al., 2017).” . It is not evident that the RANS characteristics prevent them to reproduce transient flow features. Do you mean unsteady flow features ? . Concerning turbulent kinetic energy predictions with RANS Models probab;y there are models that claim they can do this. See for example : Bartzis, J,G , Boundary-Layer Meteorology (2005) 116: 445–459 ,DOI 10.1007/s10546-004-7404-y
Lines 45 -46 : “… LES is inherently more accurate than RANS….” . It would be better to say “… LES is expected to be more accurate than RANS”. We should not forget that we have to apply LES correctly and this not always easy for open flows such as the atmospheric boundary layer.
Lines 105-107 : Concerning horizontal grid, it seems that there is a different treatment for x- and y -directions. In real problems this might impose limited degree of freedom in selecting x- and y- directions. In other words is this selection application dependent ?
Lines 110 -113 ; The inlet flow conditions are briefly discussed. The key problem here is how the upwind large eddies are introduced into the computation domain, keeping in mind that any introduced error persists downwind. Please expand.

Citation: https://doi.org/10.5194/egusphere-2024-96-RC6
- AC4: 'Reply on RC6', Sam O. Owens, 30 May 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-96/egusphere-2024-96-AC4-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-96-AC4

Sam Oliver Owens, Dipanjan Majumdar, Christopher Edward Wilson, Paul Bartholomew, and Maarten van Reeuwijk

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Short summary

Designing cities that are resilient, sustainable, and beneficial to health requires an understanding of urban climate and air quality. This article presents an upgrade to the multi-physics numerical framework uDALES, which can model microscale airflow, heat transfer and pollutant dispersion in urban environments. This upgrade enables it to resolve realistic urban geometries more accurately, and to take advantage of the resources available on current and future high-performance computing systems.


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