| Due to their prevalence in both nature and practical engineering applications, the mechanics of wakes in stratified fluids is of particular interest. The strong influence of buoyancy forces causes unique wake structures to emerge that are not present in non-stratified wakes. The flow properties and wake structures are well documented at intermediate and late times, but little information is known at early times when properties characteristic of stratified wakes first begin to appear. Optical measurement techniques, such as Particle Image Velocimetry (PIV), have been successful thus far, but do not perform well at early times when the flow is turbulent and large density variations are prevalent. This paper investigates whether a refractive index matching (RIM) technique can be used to make accurate optical measurements in early wakes.;A procedure for creating a RIM linear stratification using 100% ethanol and salt (NaCl) solutions is presented. The success of the procedure is verified by measuring perceived disturbances caused by RI differences through the wake of a towed mesh in three fluid environments: a RIM stratified fluid, a non-RIM stratified fluid, and pure water. For both stratified cases, N ≈ 0.86, Fr ≈ 10.5, and Re ≈ 22 x10 3. By comparing the three environments, the RIM procedure was found to improve resolution by reducing horizontal and vertical velocity RMS values by ≥80% and ≥75%, respectively. Furthermore, RIM perceived disturbances were reduced to levels characteristic of the single RI, pure water environment. |
