# GradientOfUnstructuredDataSet Filter versus Ansys Fluent

**URL:** https://discourse.paraview.org/t/gradientofunstructureddataset-filter-versus-ansys-fluent/3887
**Category:** ParaView Support
**Created:** [March 25, 2020, 9:24pm UTC](https://discourse.paraview.org/t/gradientofunstructureddataset-filter-versus-ansys-fluent/3887 "2020-03-25T21:24:36Z")
**Posts on this page:** 1
**Showing post:** 4

<div class="post-metadata">

### Author: ![Xabier\_Morales\_Ferez](https://discourse.paraview.org/user_avatar/discourse.paraview.org/xabier_morales_ferez/32/2890_2.png) [@Xabier\_Morales\_Ferez](https://discourse.paraview.org/u/Xabier_Morales_Ferez)
#### Post date: [March 26, 2020, 4:15pm UTC](https://discourse.paraview.org/t/gradientofunstructureddataset-filter-versus-ansys-fluent/3887/4 "2020-03-26T16:15:10Z")

</div>

Hi!  
First of all thanks for replying so fast, computing derivatives on meshes isn’t my expertise either. In principle, I’m working with 4D Flow data but I wanted to validate my WSS calculating pipeline with a simulation obtained from Ansys Fluent (which I have assumed gives corrects estimates of the WSS, maybe I’m mistaken). I used the velocity gradients to compute the stress tensor in each cell and perform the dot product with the normal of each triangular element as defined in the table below, from this [paper](https://www.annualreviews.org/doi/abs/10.1146/annurev-bioeng-100219-110055).

 ![image](https://discourse.paraview.org/uploads/default/original/2X/d/d216e8650a5353499256a2713d77d421a3c2385f.png)

I’m no expert on finite element methods, so maybe there is something wrong with this formulation. That is why I decided to compare the vorticity obtained from the `GradientOfUnstructuredDataSet` Filter and the one computed by Ansys since I assumed they both calculated the rotational of the velocity vector and should in theory be equal. To my surprise, as you can see in the image I attached on my previous post, that is not the case. Before making this thread I bumped into other posts [[1](https://discourse.paraview.org/t/why-wall-shear-stress-calculated-directly-from-my-solver-is-different-from-the-value-that-i-calculated-based-on-gradientofunstructuredgrid-from-paraview/2920), [2](https://discourse.paraview.org/t/numerics-of-gradient-of-unstructured-dataset-filter/638/16)] in which other people seem to have stumbled upon the same problem as me.

Thank you in advance!

---

_[View the full topic](https://discourse.paraview.org/t/gradientofunstructureddataset-filter-versus-ansys-fluent/3887)._