Time rotor

The time rotor was a component in the central column of the TARDIS console. While the TARDIS was in flight, the rotor rose and fell, stopping when the TARDIS reached a destination. It was associated with the 'whooshing' noise heard when the TARDIS was in flight.

The Doctor's TARDIS
As with the rest of the Doctor's TARDIS, the aesthetic design of the Time Rotor occasionally changed throughout the Doctor's travels. The Time Rotor was considered to be connected to the lower engines; hence as the TARDIS moved the rotor moved accordingly. As well as signifying the TARDIS' movement, the rotor was also known to stop working when something went wrong, e.g. the rotor stopped moving as the TARDIS engines stalled. This could be rectified thumping the console. (DW: Doctor Who)

The rotor, as it varied through designs, alternated between being a single column and a series of components that moved into each other from above and below. From the start it usually took the shape of a short transparent cylinder containing an assortment of various components, which rose, fell, and illuminated during flight, red/orange in colour. (DW: An Unearthly Child, et al.) The Fourth Doctor occasionally placed his hat atop the time rotor.

Sometime during the Doctor's seventh life, he reconfigured the TARDIS to a design in which the Time Rotor was a tall transparent tube which attached to the ceiling as well as the console, inside which were a pair of glowing opaque blue-white tube assemblies which would rise and fall opposite to each other during flight, meshing and unmeshing in the centre. (DW: Doctor Who)

The Ninth and Tenth Doctors' time rotor also reached the ceiling, and contained a glowing green transparent inner assembly of tubes. (DW: Rose) When that console room was destroyed and a new one regenerated by the TARDIS, the Eleventh Doctor was greeted by a time rotor which contained transparent bulbous inner components resembling blown glass. (DW: The Eleventh Hour)

The console in the TARDIS' secondary console room lacked a visible time rotor; in its place on the secondary console was a shaving mirror. (DW: The Masque of Mandragora)

Other TARDISes
The design of time rotor and console of the Master's TARDIS tended to mirror the Doctor's. (DW: The Ultimate Foe)

The time rotor in the Rani's TARDIS was a pair of bare rotating metallic rings rather than a cylinder. (DW: The Mark of the Rani)

The Junk TARDIS built by the Eleventh Doctor and Idris featured a short time rotor salvaged from a dead TARDIS, which was plugged into a similarly salvaged console. It contained various lights and metal components, and glowed pink when activated with a touch by Idris. (DW: The Doctor's Wife)

Behind the scenes

 * In the non-canon Dalek movie spin-offs, Dr. Who and the Daleks and Daleks' Invasion Earth 2150 A.D., the TARDIS lacked the time rotor or even a central console.