Analysis of flow visualization tests of a fishing boat suitable for Turkish waters

Türkiye sularına uygun bir balıkçı gemisinin akım görüntüleme deneylerinin analizi

Abstract

It is possible to see flow characteristics by inserting some measurement tools into any fluid flow. Furthermore, various methods are applied to make a flow visible. These methods are generally collected in two different groups. One of these groups is known as Surface Methods. The main surface methods used in flow visualization tests are as follows: 1. A method of any substance dissolves in the fluid, 2. A method of a mixture of oil and dye, 3. The tuft method Generally, the surface methods are used in ship hydromechanics. Especially, the tuft method is applied widely. In this method, the streamlines near and on a body are determined by using tufts. In this study, the flow visualization tests of the model 148/1C of the parent fishing boat 148/1 were carried out with the appendages and model propeller. In the loaded condition, some geometrical characteristics of the model used in the tests are as follows: The ratio of geometrical similarity, α is 25/3, the length, L is 2.4 meters and the block coefficient, $C_B$ is 0.378. The tuft method was applied as flow visualization method in this study. The tests were carried out in the Circulating Water Channel at Ata Nutku Ship Model Testing Laboratory operating within the faculty of Naval Architecture and Ocean Engineering at Technical University of Istanbul. The circulating water channel is largely used for flow observations and specialist tests in steady forward motion under the atmospheric pressure. The test section of the channel is 1.5 meters x 0.75 meters and maximum speed is 2 meters/second. The channel is equipped with a mechanical resistance dynamometer and Pitot tubes for velocity measurements. Flow visualization tests are also frequently performed using wooltufts and dye injection. All tests were carried out in the loaded condition (1.00xT) and highly loaded condition (1.25xT). The tufts used as flow visualization material were prepared from orlon yarns. In ten stations system, the pins with 1 millimeter diameter and 25 millimeters length were stuck with proper spaces on the stations 0, 0.5, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 8.5, 9, 9.5, 10 and the rudder axis at the portside of the model. The limits of the pins are out of the boundary layer and the pins are perpendicular to the surface of the model. The color of the tufts within the boundary layer was selected as claret red and the color of the tufts out of the boundary layer was selected as orange. The lengths of these tufts are varies between 25 millimeters and 40 millimeters. The tests in the loaded condition were carried out in the 110 value of flow potentiometer ($v_m$=1.4 m/s; $V_s$=8 knots) and 0, 50, 55 values of propeller potentiometer ($RPS_m$=0, 29.4, 32.3; RPSs=0, 10.2, 11.2). The tests in the highly loaded condition were also carried out in the 110 value of flow potentiometer (vm=1.4 m/s; Vs=8 knots) and 0, 55 values of propeller potentiometer ($RPS_m$=0, 32.3; $RPS_s$=0, 11.2). The photographs were taken with a digital camera for all the test conditions. Then, a computer aided evaluation of these photographs was performed and the conclusions are presented here. The conclusions for the loaded condition are as follows (the values of flow and propeller potentiometers are 110 ($V_s$=8 knots) and 55 ($RPS_s$=11.2) respectively): • The flow lines in the stations 9, 8.5 and 8 are regular. • The flow is normal in the region from the station 8 to the station 5. • In the station 2, the flow is normal. • In the station 1, there is turbulence at the region over the propeller. Furthermore, there is suction over the propeller and a vortex tube was observed there. • There is suction in the stations between 1.5 and 1. Here, the tufts oscillate. Bubbles on the surface of the model were also observed. • There is a backward flow on the surface of the model in the propeller disk plane. • In the region between the stations 0.5 and 0, the flow was dragged tangentially on the surface of the model. • The flow on the rudder is normal. • The flow in the back of the transom stern is also normal. The conclusions for the highly loaded condition are as follows (the values of flow and propeller potentiometers are 110 ($V_s$=8 knots) and 55 ($RPS_s$=11.2) respectively): • It is necessary to make a filling lightly on the surface between the stations 1.5 and 1. • The vortex tube happens over the propeller. • In the station 0.5, turbulence was observed in the region over the propeller.

Özet

Bu çalışmada, Türkiye sularına uygun olarak geliştirilmiş olan balıkçı gemilerinden 148/1 kodlu ana balıkçı gemisinin 148/1C kodlu modelinin yüklü (1.00xT) ve aşırı yüklü (1.25xT) yükleme durumlarındaki akım görüntüleme deneyleri, iplikçik yöntemi kullanılarak gerçekleştirilmiştir. Deneylerde kullanılan bu modelin α geometrik benzerlik oranı 25/3, L boyu 2.4 m ve CB blok katsayısı ise 0.378’dir. Deneyler, İTÜ Gemi İnşaatı ve Deniz Bilimleri Fakültesinin Ata Nutku Gemi Model Deney Laboratuvarındaki Sirkülasyon Kanalı Ünitesinde takıntılı ve model pervaneli olarak yapılmıştır. Akım görüntüleme maddesi olarak kullanılan iplikçikler, orlon iplikten hazırlanmıştır. Modelin iskele tarafındaki, 10 posta sisteminde; 0, Dümen Ekseni, 0.5, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 8.5, 9, 9.5 ve 10 nolu posta çizgileri üzerine 1 mm çaplı ve 25 mm uzunluklu çiviler, başları sınır tabaka dışında kalacak ve yüzeye dik olacak şekilde uygun aralıklarla çakılmıştır. Sınır tabaka içindeki iplikçikler bordo renkli, sınır tabaka dışındaki iplikçikler ise turuncu renkli olarak seçilmiştir. Bu iplikçiklerin boyları da [25-40 mm] arasında değişmektedir. Yüklü durumdaki deneyler 110 akım potansiyometre değerinde ($v_m$=1.4 m/s; $V_s$=8 knot) ve 0, 50 ile 55 pervane potansiyometre değerlerinde ($RPS_m$=0, 29.4, 32.3; $RPS_s$=0, 10.2, 11.2) yapılmıştır. Aşırı yüklü durumda ise 110 akım potansiyometre değerinde (vm=1.4 m/s; Vs=8 knot) ve 0 ile 55 pervane potansiyometre değerlerinde ($RPS_m$=0, 32.3; $RPS_s$=0, 11.2) yapılmıştır. Tüm bu deney koşullarında, dijital fotoğraf makinesi ile çekilen deney fotoğraflarının bilgisayar ortamında değerlendirilmesi sonucunda elde edilen bulgular maddeler halinde sıralanmıştır.