bubbleApp

<aura:application extends="force:slds">
    <lightning:card title="bubbleApp">
    <c:bubbleGrandParent/>
    </lightning:card>
</aura:application>

bubbleChild

<aura:component>
    <aura:attribute name="message" type="String" default="Hi!"/>
    <aura:attribute name="result" type="String"/>
    <aura:registerEvent name="bubbleEvent" type="c:bubbleEvent"/>
    <aura:handler name="bubbleEvent" event="c:bubbleEvent" action="{!c.showMessage}"/> 
    <lightning:layout verticalAlign ="center">
        <lightning:layoutItem padding="around-large">
            <lightning:input type="Text" name="message" label="message" value="{!v.message}"/>
        </lightning:layoutItem>
        <lightning:layoutItem padding="around-large">
            <lightning:button label="OK" onclick="{!c.sendMessage}"/>
        </lightning:layoutItem>
        <lightning:layoutItem padding="around-large">
            Child: <ui:outputText value="{!v.result}"/>
        </lightning:layoutItem>
    </lightning:layout>
</aura:component>

({
	sendMessage : function(component, event, helper) {
		console.log('send');
        component.getEvent('bubbleEvent').setParams({'message':component.get('v.message')}).fire();
	},
	showMessage : function(component, event, helper) {
		component.set('v.result',event.getParam('message'));
	},    
})

bubbleGrandParent

<aura:component >
    <aura:attribute name="result" type="String"/>
    <aura:handler name="bubbleEvent" event="c:bubbleEvent" action="{!c.showMessage}"/>    
    <lightning:layout verticalAlign ="center">
        <c:bubbleParent/>
        &nbsp;GrandParent: <ui:outputText value="{!v.result}"/>
    </lightning:layout>
</aura:component>

({
	showMessage : function(component, event, helper) {
		component.set('v.result',event.getParam('message'));
	},   
})

bubbleParent

<aura:component >
    <aura:attribute name="result" type="String"/>
    <aura:handler name="bubbleEvent" event="c:bubbleEvent" action="{!c.showMessage}"/>    
    <lightning:layout verticalAlign ="center">
            <c:bubbleChild/>
            Parent: <ui:outputText value="{!v.result}"/>
    </lightning:layout>
</aura:component>

({
	showMessage : function(component, event, helper) {
		component.set('v.result',event.getParam('message'));
	},   
})

Component Event Bubbling

<aura:event type="COMPONENT">
    <aura:attribute name="message" type="String"/>
</aura:event>