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Geometri kanal aliran yang memiliki pembesaran saluran mendadak di bagian hilir dapat menghasilkan aliran yang terpisah dan bertaut kembali (separated-reattached flow). Model geometri seperti ini salah satunya berbentuk backward facing-step yang merupakan bentuk yang sederhana dan banyak digunakan untuk melakukan simulasi berbagai macam fenomena pada peralatan keteknikan seperti reaktor kimia, sistem kendali aerodinamik kendaraan, sistem pembakaran pada dump combustor dan lain-lain. Pada aplikasinya, dinamika aliran di zona resirkulasi yang terbentuk sangat mempengaruhi kinerja operasional peralatan-peralatan tersebut. Pada penelitian ini dilakukan upaya memodifikasi ukuran zona aliran resirkulasi dengan merubah ketinggian step serta memberikan eksitasi eksternal berupa injeksi slot jet dari fluida panas dengan variasi temperatur 1000 C dan 3000 C. Kajian komprehensif dilakukan dengan pendekatan komputasional dan eksperimental. Model k-ε digunakan dalam kajian komputasi sementara medan aliran resirkulasi divisualisasi dengan menggunakan high speed camera yang kemudian diolah menggunakan image processing software sehingga dapat dianalisis lebih lanjut untuk mendapatkan
informasi mengenai berbagai fitur struktur aliran yang termodifikasi akibat pemberian eksitasi jet pada medan aliran resirkulasi tersebut. Hasil dari eksperimen dan komputasi kemudian digunakan untuk menjelaskan efek dari pengaruh ketinggian step dengan jarak injeksi yang diberikan terhadap bentuk dari zona aliran resirkulasi pada model geometri backward facing step.

Saluran aliran dengan pembesaran mendadak di bagian saluran keluar dapat menghasilkan aliran yang terpisah sehingga menyebabkan timbulnya aliran resirkulasi (separation). Model dari geometri seperti itu merupakan bentuk yang sederhana untuk mensimulasikan fenomena yang sama seperti yang terjadi pada sistem pembakaran (dump combustor),reactor kimia, peralatan elektronik CPU (central processing unit) komputer, proses elektrokimia (electroplating) dan lain-lain. Penelitian ini dilakukan dengan 2 metode yaitu : metode komputasi menggunakan software CFD (Computational Fluid Dynamics) untuk memprediksi medan aliran kecepatan, dan distribusi gas injeksi pada aliran dalam kanal berkontur tangga berupa injeksi jet panas dan metode eksperimental dengan cara melakukan pengukuran secara konvensional menggunakan termokopel.Dalam penelitian ini di fokuskan pada rasio spesifik momentum injeksi I= 0.1 dan I= 0.5 dengan jarak injeksi dari tangga lf = 2H (40mm) dan lf = 4H (80mm) serta variasi temperatur injeksi Tinj=1000C dan Tinj =3000C. Metode komputasi yang digunakan untuk menyelesaikan kondisi tersebut menggunakan metode volume hingga (finite volume method) yang mengganti persamaan-persamaan diferensial parsial dari kontinuitas, momentum, dan energi menjadi persamaan-persamaan aljabar. Model matematika yang dipergunakan untuk memvalidasi dari hasil eksperimental yang telah dilakukan terdahulu menggunakan persamaan aljabar K-epsilon dan RNG untuk kondisi slot jet (2D) dan round jet (3D). Hasil komputasi yang didapat dipergunakan untuk memvalidasi dari hasil eksperimental terdahulu yang ditujukan untuk menjelaskan efek dari geometris injeksi tersebut.

Flow channel with sudden expansion produces a separated flow so that causing a recirculation flow. This investigation is revealing the alteration of the thermal structure within the flow field due to a heated gas penetration. Main focus is placed on the influence of the ratio of specific momentum injection (I=0.1 and I=0.5), the injection location of heated gas (lf= 2H and lf=4H) and the variation of injection temperature (Ti=1000C and Ti=3000C) The investigation was done computationally using finite volume method as well as experimentally in a closed loop flow channel with a
backward-facing step flow configuration. Numerical solution models turbulence used were k-epsilon standard model and RNG k-epsilon. The numerical model was then validated by the experimental results. This model works on 2-D and 3-D Reynolds average Navier-Stokes (RANS) equations. From the results of thermal structure obtained, it can be suggested that increasing the the ratio of specific
momentum injection supports more effective thermal mixing except to the narrow region around area injection. More significant results are obtained in the region of shear layer and area downstream of the injection.

This research investigated the characteristics of convective mass transfer in a parallel plate electrochemical flow cell under the influence of turbulence induced by a wall-recess that produce a separating-reattached flow field. Wall-recess was in the form of a 5 mm rearward-facing step ontoured-channel which was placed upstream of the electrochemical cell to serve as a control device for turbulence level. Experimental work was done to elucidate the effect of fluid dynamical parameters to the rate of mass transfer between cell electrodes made of copper plates. The experimental set-up consisted of closed loop flow channel equipped with flow rate control and solution of CuSO4 of 0.5M was used as electrolyte fluid. The measurement of rate of mass transfer was done using the limiting diffusion current technique in which local limiting current measured at micro cathodes placed in the electrochemical cell would indicate the local mass transfer coefficient (Km). The current measurement was done with a precision digital multimeter interfaced by a data acquisition system to a personal computer. Some results shows that the convective mass transfer is proportionally influenced by the increase of Reynolds numbers of main flow velocity. Within the range of Re = 300 – 3000, the mass transfer coefficient increase to Km = 3.299 x 10-4 - 3.89 x 10-4 (m/s) which give some improvement up to 25.5 % of mass transfer rate compare to the case of electrochemical process with no flow condition. Furthermore, some correlations between Sherwood and Reynolds number are also discussed.

This research investigated the flow and convective heat transfer characteristics of an impinging synthetic jet with different excitation modes. The synthetic air jet was generated by a vibrating membrane which pushed out the air from the cavity through the exit nozzles with oscillatory motion. The main purpose of this synthetic jet was to create vortices pair to come out  from nozzle which will accelerate the heat transfer process occuring at the impinged wall. This heat transfer enhamcement
principles became the basis to simulate an alternative cooling system to substitute the  conventional fan cooling in electronic devices due to its advantage for having a small form factor and low noise. The Investigation combined computational and experimental works. The model was simulated to examine the distribution of heat flow on the impinged walls using a turbulent  model of k-w SST. Meshing order was elements Tet/Hybrid and type Tgrid and the number of grid was more than 230000 in order to ensure detail discretization and more accurate calculation results. In the experiment, sinusoidal, triangular and square waveform were generated with a function generator to oscillate the membranne. The frequency of membrane vibration were 80 Hz, 120 Hz, 160 Hz, and the velocity amplitude was 1 m/s. Some results  indicated significant influence of the excitation waveform to the cooling rate obtained.