Tesla　turbines　are　a　kind　of　unconventional　bladeless　turbines,　which　utilize　the　viscosity　of　working　fluid　to　rotate　the　rotor　and　realize　energy　conversion.　They　offer　an　attractive　substitution　for　small　and　micro　conventional　bladed　turbines　due　to　two　major　advantages.　In　this　study,　the　effects　of　two　influential　geometrical　parameters,　disc　thickness　and　disc　spacing　distance,　on　the　aerodynamic　performance　and　flow　characteristics　for　two　kinds　of　multichannel　Tesla　turbines　(one-to-one　turbine　and　one-to-many　turbine)　were　investigated　and　analyzed　numerically.　The　results　show　that,　with　increasing　disc　thickness,　the　isentropic　efficiency　of　the　one-to-one　turbine　decreases　a　little　and　that　of　the　one-to-many　turbine　reduces　significantly.　For　example,　for　turbine　cases　with　0.5　mm　disc　spacing　distance,　the　former　drops　less　than　7%　and　the　latter　decreases　by　about　45%　of　their　original　values　as　disc　thickness　increases　from　1　mm　to　2　mm.　With　increasing　disc　spacing　distance,　the　isentropic　efficiency　of　both　kinds　of　turbines　increases　first　and　then　decreases,　and　an　optimal　value　and　a　high　efficiency　range　exist　to　make　the　isentropic　efficiency　reach　its　maximum　and　maintain　at　a　high　level,　respectively.　The　optimal　disc　spacing　distance　for　the　one-to-one　turbine　is　less　than　that　for　the　one-to-many　turbine　(0.5　mm　and　1　mm,　respectively,　for　turbine　cases　with　disc　thickness　of　1　mm).　To　sum　up,　for　designing　a　multichannel　Tesla　turbine,　the　disc　spacing　distance　should　be　among　its　high　efficiency　range,　and　the　determination　of　disc　thickness　should　be　balanced　between　its　impacts　on　the　aerodynamic　performance　and　mechanical　stress.