# Flying hot-wire anemometry

- Received:

DOI: 10.1007/BF00266318

- Cite this article as:
- Thompson, B.E. & Whitelaw, J.H. Experiments in Fluids (1984) 2: 47. doi:10.1007/BF00266318

## Abstract

A flying hot-wire arrangement has been developed for the measurement of the velocity characteristics of the flow around airfoils, and particularly in regions where negative values of instantaneous velocity occur. The mechanism and signal processing system are described and appraised by comparing stationary and flying wire measurements obtained in the trailing edge region of a flap at an angle of attack which leads to upper-surface separation.

### List of symbols

- 〈〉
time averaged quantity

*E*voltage from hot wire anemometer

*Q*, φmagnitude and direction of cooling velocity viewed from a frame of reference on the probe: 〈

*Q*〉=〈*U*〉+〈*V*_{p}〉*q*_{1},*q*_{2},*q*_{3}cooling velocity fluctuations oriented with respect to the φ-direction

*Q*_{eff}magnitude of effective cooling velocity measured by the hot wire:

*Q*_{eff}= (*Q*_{N1}^{2}+*h*^{2}*Q*_{N2}^{2}+*k*^{2}*Q*_{T}^{2}^{1/2}*t*time

*q*_{eff}fluctuations of the effective cooling velocity

*Q*_{N1},*Q*_{N2},*Q*_{T}axial, normal and tangential components of the cooling velocity relative to the hot wire

*Q*_{eff}(Ψ= 10°)magnitude of the effective cooling velocity with

*Q*_{eff}(Ψ = 0°)*Q*_{eff}(α = 30°)magnitude of the effective cooling velocity with the wire pitched at 10 ° and 0° to the flow velocity

*Q*_{eff}(α = 45°)*Q*_{eff}(α = 30°)magnitude of the effective colling velocity with the wire yawed at 45° and 30° to the flow velocity

*U*, θmagnitude and direction of flow velocity

*u, v, w*flow velocity fluctuations (

*x, y, z*)*u*_{1},*u*_{2},*u*_{3}normalised fluctuations of cooling velocity:

*u*_{i}=*q*_{i}〈*Q*〉 for*i*=1,2,3*V*_{p}, βmagnitude and direction of probe velocity

*v*_{p}probe velocity fluctuations along the β-direction

- α
yaw angle of hot wire relative to the probe axis

- Δ
angle of mean flow velocity to the probe axis

- γ
angle of mean axial cooling component to mean cooling velocity viewed from the wire

- ψ
pitch angle of probe axis relative to tunnel coordinates (

*x, y, z*)*x, y, z*orthogonal coordinate system with the

*x*-direction aligned with the wall (boundary layer) or tunnel centre-line (wake)*x*_{w},*y*_{w},*z*_{w}orthogonal coordinate system with the

*z*_{w}-direction aligned with the wire and the probe pintels in the*x*_{w}-*z*_{w}plane