In the windless place the candle flame is always established vertically up. And there is this all the habitual phenomenon quite so, but not somehow differently, because of the physical phenomenon under the name "convection".
Convection is a physical phenomenon by means of which thermal energy is transferred to liquids or gases by mixture of the substance - as in the natural way, and forcibly. natural convections phenomenon (which can be observed when burning a candle) arises spontaneously at uneven heating of substance in the field of inclination. At spontaneous convection the located substance layers after their heating are lower become easier and rise up.
This physical phenomenon can be explained by means of Archimedes's law and also the phenomenon of expansion of bodies under the influence of thermal energy. At temperature increase the volume of a certain liquid or gas increases, density, respectively, decreases. Under the influence of Archimedes force, more rarefied, heated gas or liquid rises strictly up, and colder gas or liquid substance nearby located, meanwhile, falls down.
In a case with a candle, the air heated by its flame over a candle consisting of water vapor, carbon dioxide, etc. - rises vertically up. To the place of the risen hot air from below, parallel to the candle, cold air rises. These streams of cold air flow round a candle and give the vertical pointed form of a flame. The cold air which arrived to the place of heated heats up and replaced with the arrived stream of cold air too. This process of constant replacement of air over a candle will continue all the time while the flame of a candle heats air that constantly keeps its vertical shape. However the vertical arrangement accepts a flame of a candle only indoors in which there are no foreign influencing forces. At impact on a candle of additional forces (wind, movement of a candle) or in the absence of influence of gravity (in space) the vertical column of a flame will change the form.