Surface following nozzle, observation device for moving object surface, and observation method for moving object surface

A surface following system, comprising:

• a cooling water supplying part configured to supply cooling water to a surface of a moving object;
• and
• a surface following nozzle configured to inject gas toward the surface of the moving object, the surface following nozzle comprising:
• a nozzle having a tip end as a first end and a base end as a second end and configured to inject the gas from the tip end thereof;
• a separating part configured to close the base end of the nozzle;
• and
• an extending and contracting part that is provided at the base end of the nozzle via the separating part, and configured to extend and contract along an axial direction of the nozzle in response to changes in pressure inside the nozzle depending on a gap between the tip end of the nozzle and the surface of the moving object,
• wherein,
• the extending and contracting part includes an elastic body configured to apply a forward force with respect to the nozzle,
• when a spring constant of the elastic body is set as k [N/m], a necessary followed distance changing amount is set as xr[m], a maximum pressure of the gas that can be supplied is set as Pmax [Pa], a minimum pressure of allowable gas is set as Pmin [Pa], a nozzle discharge area is set as SN [m2], a maximum velocity of the cooling water in a vicinity of the tip end of the nozzle is set as Vmax, and a density of the cooling water is set as ρW [kg/m3], the spring constant k of the elastic body satisfies following formulas (1) and (2), and
• a contraction amount x[m] of the elastic body is within a range from xmin to xmax indicated by following formulas (3) and (4) to obtain the gas having a momentum that exceeds a momentum of the cooling water,
• k<(Pmax−Pmin)SN/xr (1)
• Pmin=ρWVmax2/2 (2)
• xmin=PminSN/k (3)
• xmax=PmaxSN/k (4).