select explicitly the main kernel in SphereGPU App

apps/gpu/SphereGPU/Sphere.cpp

@@ -70,6 +70,7 @@
 #include "VirtualFluids_GPU/Factories/GridScalingFactory.h"
 #include "VirtualFluids_GPU/PreCollisionInteractor/Probes/PointProbe.h"
 #include "VirtualFluids_GPU/PreCollisionInteractor/Probes/PlaneProbe.h"
+#include "VirtualFluids_GPU/Kernel/Utilities/KernelTypes.h"
 
 int main(int argc, char *argv[])
 {
@@ -170,6 +171,8 @@ int main(int argc, char *argv[])
         para->setTimestepOut(timeStepOut);
         para->setTimestepEnd(timeStepEnd);
 
+        para->setMainKernel(vf::CollisionKernel::Compressible::K17CompressibleNavierStokes);
+
         //////////////////////////////////////////////////////////////////////////
         // set boundary conditions
         //////////////////////////////////////////////////////////////////////////