Define the search component for clustering in solrconfig.xml:

<searchComponent name="clustering" enable="true"
 class="solr.clustering.ClusteringComponent" >
 <lst name="engine">
 <str name="name">lingo</str>
 <str name="carrot.algorithm">org.carrot2.clustering.lingo.LingoClusteringAlgorithm</str>
 <str name="carrot.resourcesDir">clustering/carrot2</str>
 </lst>
 <lst name="engine">
 <str name="name">stc</str>
 <str name="carrot.algorithm">org.carrot2.clustering.stc.STCClusteringAlgorithm</str>
 <str name="carrot.resourcesDir">clustering/carrot2</str>
 </lst>
</searchComponent>

We can also declare cluster components as engines or a multiple clustering pipeline, which can be selected by specifying the parameter clustering.engine=<engine name> in the query URL.