# Is the speed of sound constant?

I am reading the paper named, "DualSPHysics Open-source parallel CFD solver..." (https://www.sciencedirect.com/science/article/pii/S0010465514003397) and I am a bit surprised that they work with c*a and c*b ie. speed of sound of particle a and particle b. To my understanding DualSPHysics will provide every particle in the domain, the same constant initially set speed of sound?

Kind regards

## Comments

im a newby here but i think your question might be related to the WCSPH formulation, which mean "the speed of sound must be at least ten times faster than the maximum fluid velocity to keep density variations within acceptable levels of less than 1%". so, what i think is that the speed of sound is not the constant you write down at the xml file, but is constantly calculated in order to check the maximum velocity of the flow and keeping this density variations within the desired range to get close an incompressible approach