Time-mean Velocity Measurements Research Articles

Jet flow issuing from an axisymmetric pipe-cavity-orifice nozzle

An axisymmetric air jet flow is experimentally investigated under passive flow control. The jet issues from a pipe of the inner diameter and length of 10 mm and 150 mm which is equipped with an axisymmetric cavity at the pipe end. The cavity operates as a resonator creating self-sustained acoustic excitations of the jet flow. A mechanism of excitations is rather complex – in comparison with a common Helmholtz resonator. The experiments were performed using flow visualization, microphone measurements and time-mean velocity measurements by the Pitot probe. The power spectral density (PSD) and the sound pressure level (SPL) were evaluated from microphone measurements. The jet Reynolds number ranged Re = 1600–18 000. Distinguishable peaks in PSD indicated a function of the resonator. Because the most effective acoustic response was found at higher Re , a majority of experiments focused on higher Re regime. The results demonstrate effects of the passive control on the jet behavior. Fluid mixing and velocity decay along the axis is intensified. It causes shortening of the jet transition region. On the other hand, an inverse proportionality of the velocity decay ( u ~ 1/ x ) in the fully developed region is not changed. The momentum and kinetic energy fluxes decrease more intensively in the controlled jets in comparison with common jets.

Enhancement of synthetic jets by means of an integrated valve-less pump: Part II. Numerical and experimental studies

The paper studies the performance of the new fluid jet actuator based on the novel principle of the generation of fluid jet, which has been presented in [Z. Trávníček, A.I. Fedorchenko, A.-B. Wang, Enhancement of synthetic jets by means of an integrated valve-less fluid pump. Part I. Design of the actuator, Sens. Actuators A, 120 (2005) 232–240]. The fluid jet actuator consists of a synthetic jet actuator and a valve-less pump. The resulting periodical fluid jet is intrinsically non-zero-net-mass-flux, in contrast to the traditional synthetic jet. The numerical results have been compared with the laboratory experiments comprising phase-locked smoke visualization and time-mean velocity measurements. The results have confirmed the satisfactory performance of the actuator.

Aerodynamic flow investigations in an isothermal model of an afterburner

Experimental and numerical investigations of the three-dimensional flowfields in an isothermal model of an afterburner are presented. Five-hole pilot probe measurements along the entire length of the model in three different azimuthal planes, allow the determination of three mean velocity components which provide comprehensive information to aid understanding of such complex flows. The numerical calculations are performed using a SIMPLE based algorithm with staggered grid arrangement. The standardk-ɛ model is used for physical modeling. The numerical results agree quite satisfactorily with the time-mean velocity measurements. The predicted turbulence kinetic energy contours have also been presented.

Separated Flow in a Low-Speed Two-Dimensional Cascade: Part I—Flow Visualization and Time-Mean Velocity Measurements

This study was conducted for the purpose of providing a more fundamental understanding of separated flow in cascades and to provide performance data for fully stalled blade rows. Cascades of a single blade geometry and a solidity of unity were studied for three stagger angles and the full range of angle of attack, extending well into the stalled flow regime. Results are presented from flow visualization and time-mean velocity measurements of stalled flow in the cascade. Surface and smoke flow visualization revealed that the blade stagger angle is a key parameter in determining the location of the separation line and the occurrence of propagating stall. Time-mean velocity measurements obtained with a dual hot split-film probe also showed that the separated velocity profiles within the blade passages and the profiles in the wake have distinctly different characteristics depending on the stagger angle.