lightning:select selected value is not set

I am very new to Aura component and Salesforce, I am trying to have a drop down which allow the user to pick from the list. the values of the list come from sobject. I looked into many online examples on how to do the LIghtning:Select, but I always get undefined for the selected value. Can anyone help me to figure out how?

—- aura component code —

<div>
    <lightning:select aura:id="lstProjectEpic" name="lstProjectEpic" label="Project Epics"    >
  <aura:iteration items="{!v.lstProjectEpic}" var="epic">
         <option value="{!epic.Name}" selected="{!epic.selectedValue}" > {!epic.Name}</option>
   </aura:iteration>
  </lightning:select>
</div>

—- in the controller i have this code to get the selected value, and then pass it as the parameter to the Apex code method —

    var selectedEpic =component.find("lstProjectEpic").get("v.value"); 
     console.log("selected Project Epic " + selectedEpic);

Console log shows the value is always undefined. Do i need to do anything extra?

I also want to set the Select a default value when the page is first loaded and then when the value is selected, it calls the apex codes to retrieve and display the data based on the selected option and display the data back. I don’t know how to set default value either. I put such action in the init handler. Please advise.

—- updated

I realized the lightning:select cannot be used for multi options. I changed to use DualListBox. I tried to reload the page with the list of projects based on the selected criteria, so i put it the handleChange event, and call the helper which will set the parameter of the apex code using the selected values from the duallistbox, and then page gets reloaded with new list of projects. I am not quite sure how to pass the selected values to the apex code and where to set the page reload. I got helper.getProjectAndTasks(component, event, helper) in the handleChange event.

—Aura Component code —

  <aura:attribute name="options" type="List" default="[]"/>
<aura:attribute name="values" type="List" default="[]"/>



<lightning:dualListbox name="multipleOptions"  
                       label= "Departments" 
                       sourceLabel="Available" 
                       selectedLabel="Selected" 
                       options="{!v.options}" 
                       value="{!v.values}" 
                       onchange="{! c.handleChange }"/>

—- controller —

({
      doInit : function(component, event, helper) {
      helper.getProjectAndTasks(component, event, helper);
      // helper.getNotes (component, event, helper);
      // helper.getProjectEpics(component, event, helper);

      //  helper.getNewEpicValue (component,event,helper);
      helper.getUserProfile(component, event, helper);
      helper.getDepartments(component, event, helper); 
   },

   handleChange: function (cmp, event) {
       // This will contain an array of the "value" attribute of the selected options
       var selectedOptionValue = event.getParam("value");
       // alert("Option selected with value: '" + selectedOptionValue.toString() + "'");

    console.log("Option selected with value: '" + selectedOptionValue.toString() + "'"); 

    helper.getProjectAndTasks(component, event, helper);
   }
  })

— helper —

  ({
        getProjectAndTasks : function(component, event, helper) {


            var selectedOptionValue = event.getParam("value");

      var   action = component.get('c.getProjectWithTaskAndNotesByEpic');
         action.setParams({ "Departments" : selectedOptionValue });


            action.setCallback(this,function(response)
                       {
                           var state= response.getState();
                           if(state == "SUCCESS")
                           {
                               console.log('reponse : ' + response.getReturnValue());
                               var proj = response.getReturnValue();



                               component.set('v.lstProject',response.getReturnValue());
                           }
                       });
                       $A.enqueueAction(action);
},
getDepartments : function  (component, event, helper){

                var action = component.get('c.getDepartments');
            action.setCallback(this,function(response)
                       {
                           var state= response.getState();
                           if(state == "SUCCESS")
                           {
                                var departments =response.getReturnValue();
                               console.log('Departments are : ' + departments);                         
                                var items =[];
                               for(var d in departments)
                               {
                                             var item = {
            "label":  departments[d] ,
            "value":  departments[d]   
        };
                                               items.push(item);
                               }
                               component.set('v.options',items);

                           }
                       });
                       $A.enqueueAction(action);    


   }
})

— apex controller —

@AuraEnabled
public static List<String> getDepartments(){
           List<department__c> departments = new List<department__c>();
        departments = [select  name  from  department__c  ]; 
    System.debug(departments.size());
    List<String> deptName = new List<String>();
    for(department__c d : departments){
        deptName.add(d.Name);
    }
    return  deptName ;
}

     public static List<ProjectWrapper> getProjectWithTaskAndNotesByEpic( ){
      ------logic to pull the proejct related coe
  }

<aura:attribute name="selectedEpic" type="String" />

<lightning:select aura:id="lstProjectEpic" value="{!v.selectedEpic}" name="lstProjectEpic" label="Project Epics" >

console.log("selected Project Epic " + component.get("v.selectedEpic"));

component.set("v.lstProjectEpic",[
            {Name:'qwe'},{Name:'asd',selectedValue:true},{Name:'zxc'}
        ]);

<aura:component>
    <aura:attribute name="status" type="String" default="open"/>
    <aura:handler name="change" value="{!v.status}" action="{!c.handleChange}"/>
    <lightning:select aura:id="select" name="select" label="Opportunity Status" value="{!v.status}">
        <option value="">choose one...</option>
        <option value="open">Open</option>
        <option value="closed">Closed</option>
        <option value="closedwon">Closed Won</option>
    </lightning:select>
    <lightning:button name="selectChange" label="Change" onclick="{!c.changeSelect}"/>
</aura:component>

handleChange: function (cmp, event, helper) {
    //Do something with the change handler
    alert(event.getParam('value'));
}