Numerical Investigation on Handling Stability of a Heavy Tractor Semi-Trailer under Crosswind
Round 1
Reviewer 1 Report
This study deals with a numerical investigation on handling stability of heavy tractor semi-trailer under crosswind. First, aerodynamic characteristics were calculated by CFD, and then, the analysis of the multi-body dynamics considering aerodynamic characteristics was carried out and analyzed to handle the stability of a heavy tractor with a semi-trailer. The effect of a deflector on the lateral acceleration and yaw rate was performed numerically. Thus, the claimed issue regarding this approach may be important for readers in this journal.
However, to improve the quality of the manuscript, major revisions are needed, as detailed in the follows:
- In the introduction, the proposed issues were that the aerodynamic characteristics under different crosswinds were computed by CFD, and a mathematical model was constructed to describe the relationship between aerodynamic forces and crosswind.
Basically, in this work, aerodynamic characteristics were steady-state results and multi-body dynamics was a transient approach. So, the proposed approach seems to be not considered the interaction with two analysis. It seems to be a one-way approach. More comments for the originality of this work are needed in the introduction.
- The description of the equations and units is not clear. (In the line 119~120, 180 and 181, etc.)
- In the line 190, what is the mean of non-stationary?
- In the numerical method and validation, CCM+ seems to be used in this work. Comments about the commercial code and reference need and added.
- In paragraph 4.5, there are no explanations of the optimized wind deflector. Does the wind deflector optimized from aerodynamics characteristics or from vehicle dynamics?
Author Response
The point-by-point response to the reviewer’s comments is list below in the pdf file.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Paper deals with investigation of aerodynamics effects on handling stability of semi-trailer heavy tractor. Authors made thorough overview of actual state of given problematic declared with references. Analytical model for flow field environment was defined. Numerical CFD methods was used to solve this models. First part is dedicated to validate numerical model with experiments and also other author’s research results on the same model.
Next part consists calculations of aerodynamics coefficients as function of yaw angle. After the CFD calculations, distribution pressure due to aerodynamics is discussed.
The aim is to define aerodynamics characteristics in function form where independent variable is yaw angle and accordingly use it in dynamical multibody model simulations to judge the particular vehicle crosswind handling stability and influence of wind deflector on it.
Authors concluded, that wind deflector can improve crosswind stability of heavy tractor.
I have following remarks:
Governing equations of flow field are defined but the method of their solution should be better described so the reader has clear idea how the numerical discretized model was defined and conditioned. Author just concluded that analytical equations was discretized using a vertex centered unstructured finite volume method but didn’t mention how and what software was used for model definition and solution.
Authors declared, that numerical model is the same as that used in the work of Xu Gong [19], but results in Figure 6. slightly differ from Gong`s results. This should be justify in the text.
Multi body dynamical model should be better described, so the reader can have better image of it. Schematics could be included.
In Table 1. Terms damping stiffness is not correct, it should be just damping
All over the text gaps are missing between parenthesis of citations and text.
Figures should be referenced as Figure x. not Figure. x in some part of the text.
Line 107,113 – math characters are not aligned with text.
Line 108 – all scalar variables should be in italic form such as in the equations.
Line 119, 120 – scalars in italic and indexes should be in smaller font.
Pros: Work is clear and logical. All the results a discussed and concluded. Methodology of calculation aerodynamics coefficients as function of yaw angle can bring more accurate heavy truck multibody system simulations including aerodynamic effects.
Cons: Numerical models both CFD and multi body should be better described. Text should be revised due to a lot of formal mistakes.
Author Response
The point-by-point response to the reviewer’s comments is list below in the pdf file.
Author Response File: Author Response.pdf
Reviewer 3 Report
This is an interesting paper presenting a set of useful engineering results. I was particularly interested in reading your paper as I must be one of the few academics who have driven these vehicles.
Line 35 - a sequence of scenes... rather than sequential.
Line 40 aerodynamics.
Line 41 aerodynamics.
Line 43 field.
Line 47 replace 'the driver's manipulative behaviour' (totally the wrong phrase) with 'the driver's handling of the vehicle. The following sentence 'beyond all question...crosswind stability' needs rephrasing or dropping, as it reads as a self-evident statement.
Line 66 This sentence reads badly in its present state especially the 'decrease the total lift'. Please rephrase and clarify.
Line 100 The role of the turbulence model is more limited than the computation of the flow field as suggested by the sentence. On this matter still, the authors focus on a deeply separated flow regime with a turbulence model that is notorious for its underprediction of separation. Do you care to comment, please, on why this turbulence model was employed?
Line 107 - 108 The mean and fluctuating quantities should be presented as in Equation 2 exactly in the same italic font.
Line 128 A flat surface was added.
Line 160 This sentence which starts 'Due to the geometrical similarity...' is grammatically incorrect in its current state. It has no verb.
The following sentence starting on line 161, 'The deflector has been removed...' needs rewriting probably by replacing 'and' with 'to'.
Line 170 The blockage ratio with respect to the cross section area...
Line 171 Replace typically with typical. A note on the use of the word 'yaw' for the inflow direction: In wind turbines, as indeed in good vehicle publications, the expression 'yaw' is reserved for the angular variation of the body in relation to some datum referential. Cars yaw by a very few degrees under crosswind conditions. The flow, in my book, does not yaw. I think it is safer and clearer to talk about relative inflow angular orientation and restrict the use of the word 'yaw' to the angular displacement of the vehicle in relation to the longitudinal direction.
Line 179 Is the surface corresponding to the ground stationary? I think it should be moving in relation to a stationary domain with the same velocity as that of the speed of the vehicle.
Line 179 The word 'density' is written twice.
Line 180 The Reynolds Number is, drop 'amounted to'.
Line 181 10 to the power 7, not 107.
Line 185 Drop the word 'which'. Line 192 I suggest you describe the meshes as coarse, medium and fine, not coarse, fine and finer.
Line 199 replace the word 'drive' with 'drives'. Line 199 There is the problem with the yaw angle. The reader will be left wondering if you are talking about the orientation of the vehicle or the direction of the relative flow.
Re Figure 8 and elsewhere, nobody calls the surface of the road 'floor'. It is better to use the words 'road surface'.
Still on Figure 8, I would align the vectors on the freestream inlet longitudinally and the crosswind vectors orthogonally to the freestream.
Line 200 The Beaufort scale numbers are more commonly designated as 'levels' rather than 'grades'.
Line 217 Replace 'synthetic' with 'relative' or 'resultant'.
Line 225 Replace 'tires' with 'tyres'.
Line 239 Replace 'to get the change rule' with 'to identify the mathematical relationship...'.
Figure 11 You should really replace 'yaw angle' with 'relative inflow angle' because you talk about 'yawing moment', which referred to the vehicle, and this is a sure way to confuse the reader.
Before we go any further, on page 7 the authors jumped straight from the computational grid discussion to the results section. Please can you add a small section describing the solution parameters (solver, discretization scheme, convergence criterion etc). Personally after rereading the paper several times, I am not sure if the solutions were obtained with steady state or transient simulations. If they are unsteady, clarification regarding the time step as well as post processing details are required.
Page 271 replace 'complicated vortexes' with 'complex vortices'.
Figure 12 and elsewhere, the choice of the Beaufort Scale is understandable but most engineers would prefer, and expect, to see the flow field around the truck described by SI units ie metres per second, m/s.
Line 325 What is meant by 'attitude of the vehicle'? Do you mean angular variation?
Line 348 The authors write, 'In the simulation, the driving speed was set at 30 m/s, and a constant crosswind with different strength is added in the vertical direction of the vehicle driving direction.' This is a highly puzzling sentence. What do you mean ' a constant crosswind with different strength'? I suggest you drop the 'constant'. The bit about 'vertical direction of the vehicle driving direction' is wholly obscure to me and I would expect to most readers.
Line 350 This sentence makes no sense in its present state. I suggest, 'at some stage... ...could indicate a lowering of the handling stability...'
Table 1 Replace 'tire' with 'tyre' here and elsewhere throughout the paper.
Also in Table 1 you have two different unit representations for moments of inertia.
Line 353 I don't understand why you have two different units for the driving speed and the crosswind speed. You should use only SI units, m/s.
Figure 14 The legends are incomplete, no units.
Still on Figure 14 These results are plotted as a function of time over a ten second period. That is not explained fully in the text. Please clarify.
Line 375 Figure 15 mentioned twice.
Line 377 I couldn't see alpha defined anywhere.
Line 404 Comparing the two results...
Line 419 replace 'change rule' with 'mathematical relationship' or equivalent.
Line 414 Conclusions. This section is very poor. Essentially, it is a recap of the work not a presentation of the key findings which is what a Conclusions section should focus mostly on. It is fine to have a small recap section but the key findings, qualitatively and quantitatively, should be prominent in the Conclusions section.
Author Response
The point-by-point response to the reviewer’s comments is list below in the pdf file.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The revised manuscript has improved considerably and so, I agree to publish as applied science after minor revision.
In the governing equation, the flow field in CFD is expressed as three-dimensional, turbulent, unsteady, and incompressible flow.
However, the proposed approach with eq(1) seems to be steady-state. Some comments are needed.
Author Response
Dear reviewer,
Thank you very much for you comments and suggestions. We appreciate for your warm work earnestly, and hope that corrections will meet with approval. The response is listed in the PDF file below.
Author Response File: Author Response.pdf
