diff --git a/HySoP/hysop/operator/adapt_timestep.py b/HySoP/hysop/operator/adapt_timestep.py
index 8be591f91162d9b8f28e9405266e664e1f2f697d..b3c545633d10e02d4c9b924f98da0d79aa62f085 100755
--- a/HySoP/hysop/operator/adapt_timestep.py
+++ b/HySoP/hysop/operator/adapt_timestep.py
@@ -25,12 +25,12 @@ class AdaptTimeStep(Operator):
                  dt_adapt=None,
                  method={TimeIntegrator: RK3, SpaceDiscretisation: FD_C_4,
                  dtAdvecCrit: 'vort'},
-                 topo=None, ghosts=None, **other_config):
+                 topo=None, ghosts=None, prefix='./dt.dat', **other_config):
         """
         Create a timeStep-evaluation operator from given
         velocity and vorticity variables.
 
-        Note : If cfl is None, the computation of the adaptative time step 
+        Note : If cfl is None, the computation of the adaptative time step
         is only based on dt_advection and dt_stretching, taking the minimum
         value of the two.
 
@@ -39,9 +39,9 @@ class AdaptTimeStep(Operator):
         @param resolutions : grid resolution of velocity and vorticity
         @param dt_adapt : adaptative timestep variable
         @param method : solving method
-        default = finite differences, 4th order in space for gradU evaluation 
+        default = finite differences, 4th order in space for gradU evaluation
         (used in dt_advection computation)
-        and Runge-Kutta 3 in time (used in dt_stretching computation) and 
+        and Runge-Kutta 3 in time (used in dt_stretching computation) and
         criterion for advection time step evaluation.
         @param topo : a predefined topology to discretize velocity/vorticity
         @param ghosts : number of ghosts points. Default depends on the method.
@@ -60,6 +60,7 @@ class AdaptTimeStep(Operator):
         self.dt_adapt = dt_adapt
         ## Numerical methods for time and space discretization
         self.method = method
+        self.prefix = prefix
         assert SpaceDiscretisation in self.method.keys()
         assert TimeIntegrator in self.method.keys()
         if not dtAdvecCrit in self.method.keys():
@@ -100,7 +101,7 @@ class AdaptTimeStep(Operator):
             AdaptTimeStep_D(self.discreteFields[self.velocity],
                             self.discreteFields[self.vorticity],
                             self.dt_adapt,
-                            method=self.method,
+                            method=self.method, prefix=self.prefix,
                             **self.config)
 
         self.discreteOperator.setUp()
diff --git a/HySoP/hysop/operator/discrete/adapt_timestep.py b/HySoP/hysop/operator/discrete/adapt_timestep.py
index 93cb81ff72095935ba8b5e840132c776d365a62e..3804b7c881fa77b2614840adcd0e7a6a8e789d41 100755
--- a/HySoP/hysop/operator/discrete/adapt_timestep.py
+++ b/HySoP/hysop/operator/discrete/adapt_timestep.py
@@ -35,7 +35,7 @@ class AdaptTimeStep_D(DiscreteOperator):
                  dt_adapt=None,
                  method={TimeIntegrator: RK3, SpaceDiscretisation: FD_C_4,
                  dtAdvecCrit: 'vort'},
-                 lcfl=0.125, cfl=0.5):
+                 lcfl=0.125, cfl=0.5, prefix='./dt.dat'):
         """
         @param velocity : discrete field
         @param vorticity : discrete field
@@ -77,7 +77,7 @@ class AdaptTimeStep_D(DiscreteOperator):
         # Definition of criterion for dt_advec computation
         self.dtAdvecCrit = self.method[dtAdvecCrit]
 
-        self.prefix = './res/dt_adaptative.dat'
+        self.prefix = prefix
         if (main_rank == 0):
             self.f = open(self.prefix, 'w')
 
@@ -88,7 +88,7 @@ class AdaptTimeStep_D(DiscreteOperator):
                                          self.velocity.nbComponents)
 
         # gradU function
-        self._function = GradV(self.velocity.topology, 
+        self._function = GradV(self.velocity.topology,
                                method=self.method[SpaceDiscretisation])
         memshape = self.velocity.data[0].shape
         worklength = self.velocity.nbComponents ** 2
@@ -190,7 +190,7 @@ class AdaptTimeStep_D(DiscreteOperator):
                 self.dt_adapt.data[0] = min(dt_advec, dt_stretch, dt_cfl)
 
             self.dt_adapt.data[0] = \
-                self.velocity.topology.topo.allreduce(self.dt_adapt.data[0], 
+                self.velocity.topology.topo.allreduce(self.dt_adapt.data[0],
                                                     PARMES_MPI_REAL, op=MPI.MIN)