[adiraman9]

A long time lurker of this community, all my questions and issues were already solved by searching through this vast community ! I however have an issue that seems rather strange to me, so i was hoping you guys might help shed some light on this.
I am using a solver modified from pimpleDyMFoam to solve for passive scalar in the domain (it's a generic jet in crossflow problem) and using the dynamicFvRefineMesh to adapt the mesh to the vorticity magnitude. I used snappyHexMesh to generate the mesh. Here's the checkMesh results before starting the simulation:-

Checking geometry...
    Overall domain bounding box (-0.03999999911 -0.02000255726 -0.3199999928) (0.2800000012 0.6399999857 0.3199999928)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (-6.060718881e-14 1.291685911e-13 -2.303600518e-14) OK.
    Max cell openness = 5.400546049e-16 OK.
    Max aspect ratio = 24.14037861 OK.
    Minimum face area = 2.946087816e-09. Maximum face area = 0.0005165836257.  Face area magnitudes OK.
    Min volume = 6.73982538e-13. Max volume = 1.175411952e-05.  Total volume = 0.1310735564.  Cell volumes OK.
    Mesh non-orthogonality Max: 64.79991779 average: 3.047065537
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 1.625462248 OK.
    Coupled point location match (average 0) OK.
    Face tets OK.
    Min/max edge length = 1.592653958e-05 0.02254557784 OK.
   *There are 92 faces with concave angles between consecutive edges. Max concave angle = 32.20257068 degrees.
  <<Writing 92 faces with concave angles to set concaveFaces
    Face flatness (1 = flat, 0 = butterfly) : min = 0.9117923961  average = 0.9999967098
    All face flatness OK.
    Cell determinant (wellposedness) : minimum: 0.001550385698 average: 6.801338517
    Cell determinant check OK.
 ***Concave cells (using face planes) found, number of cells: 8402
  <<Writing 8402 concave cells to set concaveCells
    Face interpolation weight : minimum: 0.03132999624 average: 0.4940655109
 ***Faces with small interpolation weight (< 0.05) found, number of faces: 16
  <<Writing 16 faces with low interpolation weights to set lowWeightFaces
    Face volume ratio : minimum: 0.02173256797 average: 0.9794945019
    Face volume ratio check OK.

Failed 2 mesh checks.

The max non-orthogonality here is about 65, However after about a thousand time steps, the non-orthogonality increases. Here's the checkMesh result for the next time directory :-

Checking geometry...
    Overall domain bounding box (-0.03999999911 -0.02000255726 -0.3199999928) (0.2800000012 0.6399999857 0.3199999928)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (-1.020092674e-14 1.188726109e-13 -3.679502457e-14) OK.
    Max cell openness = 5.508432446e-16 OK.
    Max aspect ratio = 24.14037859 OK.
    Minimum face area = 7.546356897e-10. Maximum face area = 0.0005165836257.  Face area magnitudes OK.
    Min volume = 1.232590365e-13. Max volume = 1.175411952e-05.  Total volume = 0.1310735564.  Cell volumes OK.
    Mesh non-orthogonality Max: 83.10049294 average: 4.794040349
   *Number of severely non-orthogonal (> 70 degrees) faces: 44534.
    Non-orthogonality check OK.
  <<Writing 44534 non-orthogonal faces to set nonOrthoFaces
    Face pyramids OK.
    Max skewness = 1.893790671 OK.
    Coupled point location match (average 0) OK.
 ***Error in face tets: 40 faces with low quality or negative volume decomposition tets.
  <<Writing 40 faces with low quality or negative volume decomposition tets to set lowQualityTetFaces
    Min/max edge length = 7.963269329e-06 0.02254557784 OK.
   *There are 100 faces with concave angles between consecutive edges. Max concave angle = 32.20257105 degrees.
  <<Writing 100 faces with concave angles to set concaveFaces
    Face flatness (1 = flat, 0 = butterfly) : min = 0.9015482556  average = 0.9999956346
    All face flatness OK.
    Cell determinant (wellposedness) : minimum: 0.002197372934 average: 8.207526567
    Cell determinant check OK.
 ***Concave cells (using face planes) found, number of cells: 25810
  <<Writing 25810 concave cells to set concaveCells
    Face interpolation weight : minimum: 0.0144084187 average: 0.4932446695
 ***Faces with small interpolation weight (< 0.05) found, number of faces: 56
  <<Writing 56 faces with low interpolation weights to set lowWeightFaces
    Face volume ratio : minimum: 0.006704875336 average: 0.9756846993
 ***Faces with small volume ratio (< 0.01) found, number of faces: 2138
  <<Writing 2138 faces with low volume ratio cells to set lowVolRatioFaces

Failed 4 mesh checks.

The solution eventually blows up, i think it is because of this increasing non-orthogonality. I am going to try improve the initial mesh quality and try to see if this problem persists but in the meanwhile any insight into this erroneous behavior is highly appreciated !