Numerical Simulation of a Synthetic Jet Actuator for Active Flow Control

Abstract

This chapter presents the results of numerical investigations of a synthetic jet actuator for an active flow control system. The Moving–Deforming-Mesh (MDM) method as a boundary condition is used to capture the real physical phenomenon and investigate the influence of the membrane amplitude, the forcing frequency, and cavity effect on the jet velocity. Different cases are investigated to maximize the jet velocity—an actuator with one and two membranes in a cavity, with perpendicular and parallel membranes. Two main forcing frequencies can be specified in the synthetic jet actuator application. One corresponds to the diaphragm natural frequency, and the other corresponds to the cavity resonant frequency (the Helmholtz frequency). Results of actuators operating at the two abovementioned forcing frequencies are presented. The simulation results show an increase in the jet velocity as a result of an increase in the membrane peak-to-peak displacement. Synthetic jet actuators’ impact on the flow separation reduction will be investigated on the bump model. Preliminary simulation results of the flow separation over the bump are presented in this chapter as well.

Appendix

Code of the user-defined function file used in the 2D synthetic jet actuator numerical simulation with Moving–Deforming-Mesh method is presented below:

 #include "udf.h"  /^* Put proper values in VALUE(variable) places ^*/  #define freq 740     /^* forcing frequency, Hz^*/  #define amp 0.00008    /^* peak-to-peak amplitude, meters     0.00006^*/  #define L 0.025 /^* chamber's width/membrane's diameter, meters^*/  DEFINE_GRID_MOTION(moving_membrane, domain, dt, time, dtime)  {  Thread ^*tf = DT_THREAD (dt);  face_t f;  Node ^*node_p;  real omega, alpha, y, x;  int n;  /^* Set/activate the deforming flag on adjacent cell zone, which ^*/  /^* means that the cells adjacent to the deforming wall will also be ^*/  /^* deformed, in order to avoid skewness. ^*/  SET_DEFORMING_THREAD_FLAG (THREAD_T0 (tf));  omega = 2.^*M_PI^*freq;  alpha = omega ^* CURRENT_TIME;  begin_f_loop (f, tf)  {  f_node_loop (f, tf, n)  {  node_p = F_NODE (f, tf, n);  /^* Update the current node only if it has not been previously visited: ^*/      if (NODE_POS_NEED_UPDATE (node_p))  {      /^* Set flag to indicate that the current node's position has ^*/      /^* been updated, so that it will not be updated during a future ^*/      /^* pass through the loop: ^*/  NODE_POS_UPDATED (node_p);  y = NODE_Y (node_p);  x = amp^*sin(alpha)^* ((1-((y-L)/L)^*((y-L)/L))^*(1-((y-L)/L)^*((y-L)/L)));  NODE_X (node_p) = x; } } }  end_f_loop (f, tf);  }