Jean-Claude Lecordier

The control of vortex shedding behind heated circular cylinders at low Reynolds numbers

We report some experiments undertaken to investigate the control of vortex shedding behind electrically heated cylinders at low Reynolds numbers owing to the heat input brought to the cylinder. In airflow, depending on the Reynolds number value, complete suppression or modification of the vortex shedding phenomenon can be achieved with increase of heat input. Experimental results suggest that this control could result of a slight change of the separation point location due to the increase of the dynamic viscosity of the fluid.

Frequency response of fine wire thermocouple

A theoretical and experimental study of the frequency response of fine wire thermocouples is presented. Influence of sensor geometry and flow parameters on the behaviour of transfer functions is given. Comparison between time constants obtained from internal heating technique (IHT) and external heating technique (EHT) shows significant differences due to the nonhomogeneous heating of the wire by both Joule and Peltier effects when IHT is used.

Dispersion measurements in turbulent flows (boundary layer and plane jet)

Temperature measurements concerning dispersion of heat downstream of a steady line source located successively in a boundary layer and in a plane jet are presented and discussed Temperature statistics obtained in these two turbulent flows are compared in a satisfactory way using a rescaling scheme based on the value of the temporal integral Lagrangian scale of the vertical velocity fluctuation at the source location A simple diffusion model has been developed and is qualitatively in agreement with experimental results in the first phase of the diffusion process

Correction of temperature fluctuation measurements using cold wires

It has been shown previously that the frequency response of cold wires used to measure a turbulent temperature field can be noticeably attenuated because of thermal inertia of the wire, end conduction heat loss between wire and prongs, and spatial resolution. The correction of temperature signals is, therefore, indispensable. The transfer functions of cold wires have been determined by using a home-made dynamic calibration system. A theoretical analysis is used to take into account spatial resolution. The proposed method of correction for temperature fluctuation spectra and RMS intensity accounting for these three effects is applied to the determination of temperature variance profile in the heated wake of a line source in a turbulent boundary layer.

Influence of Wollaston wire and prongs on the response of cold wires at low frequencies

Abstract This paper deals with the theoretical and experimental study of heat conduction loss for a platinum wire used as a temperature sensor when the influence of Wollaston wire is taken into account. In this case the transfer function at low frequencies can be noticeably modified. An experimental investigation of this phenomenon has been undertaken using a procedure which allows temperature fluctuations to be produced in a larger range of frequencies than has been usually made until now.

Influence de la conduction sur la fonction de transfert des fils froids dans les tres basses frequences; resultats experimentaux

Abstract This paper is devoted to the experimental study of the influence of conduction between a wire used as a sensor of temperature and its prongs on measurements of temperature variances and spectra. The difference in the behaviour of a wire of aspect ratio l /d between static conditions (calibration) and dynamical conditions (measurements in a turbulent temperature can be noticeable. This can involve an important underestimation of variances and spectra if no correction is made.

Mesure de la fonction de transfert d'un fil utilise comme capteur de temperature; Influence de la conduction

Abstract This paper deals with an experimental set-up allowing to determine frequency response of wires used as sensors of temperature fluctuations. Some spectra concerning such wires with different aspect ratios l/d are also given and influence of conduction is discussed.

Comparaison entre les methodes de determination du temps de reponse d'un fil utilise comme capteur de temperature

Several authors have noticed that values of time constants of thin wires used as a sensor of temperature fluctuations strongly depend on methods of determination. This paper deals with three different methods and proposes an explanation for the great discrepancy between time constants.

Instabilities induced in a laminar jet by acoustic hot-wires

Abstract Controlled and local excitation of a laminar flow is achieved by means of hot-wires heated periodically by Joule effect and generating acoustic waves. Some preliminary results are presented for the case of a laminar round jet.

COMPARISON OF METHODS FOR DETERMINATION OF RESPONSE-TIME OF WIRES USED AS TEMPERATURE SENSORS

Several authors have noticed that values of time constants of thin wires used as a sensor of temperature fluctuations strongly depend on methods of determination. This paper deals with three different methods and proposes an explanation for the great discrepancy between time constants.