Akansu, Yahya Erkan; Fırat, Erhan; Hacıalioğulları, Mustafa

This experimental study focused on the concurrent minimization of the mean and fluctuating forces acting on a square prism in crossflow by creating a continuous jet through a narrow spanwise slot in it. For this purpose, three different predetermined injection surfaces (i.e., front, top, and rear) were individually studied for the injection ratios (IR) of 0, 1, 1.5, 2, 2.5, and 3 at a Reynolds number (Re) of 8000. The results showed that the rear jet is the optimum injection surface. For the rear jet configuration, the optimum IR is 1.5 in terms of mean total drag coefficient reduction, 〈CDT〉. In this case, the reductions in the 〈CDT〉 and the level of root mean square (RMS) of fluctuating pressure coefficient (CP RMS) on the side surfaces are about 29.7% and 68%, respectively. However, the maximum reduction in the CP RMS level on the side surfaces occurred at IR = 2. In this case, the reductions in the 〈CDT〉 and the level of CP RMS on the side surfaces are about 27.5% and 88%, respectively. The underlying mechanism of force reduction was also demonstrated. Various flow patterns were identified with respect to IR at incidence angle (α) of 0°. It was also proved that, at relatively small angles of incidence, from α = 0° to 20°, the active flow control method is still effective in reducing 〈CDT〉 and in suppressing the fluctuating side forces, which is indicative of periodic vortex shedding from either side of the square prism.

AtıfScopus18·WoS18·OpenAlex18

İncele

Firat, Erhan; Özmert, Mehmet; Akansu, Yahya Erkan

Bu çalışmada, pasif akış kontrol elemanı olarak kullanılan dairesel kesitli bir çubuk ile kare kesitli bir küt cisimetrafındaki akış durumunda hücum açısının girdap kopma olayına etkisi deneysel olarak incelenmiştir. Hücumaçısının değeri 0°’ye eşit iken öndeki kontrol çubuğu ile kare model serbest akışa göre ardışık olarak durmaktadırlar.Deneyler Reynolds sayısının 1.0 x 10⁴değerinde, d/D=0.25 çap oranında, hücum açısının 0°leq alpha leq⁹⁰ aralığında, ikicisim arasındaki boyutsuz mesafe olan L/D’nin 1, 2, 3 ve 4 değerlerinde gerçekleştirilmiştir. Hız ölçümleri sabitsıcaklık anemometresi (CTA) ile yapılmış olup, girdap kopma frekansları hız-zaman değişiminin spektral analizindenelde edilmiştir. Duman tel yöntemi ile akış görünür hale getirilerek akış ayrılması, yeniden tutunması ve girdapoluşum bölgesinin özellikleri ortaya konulmuştur. L/D=2 ve 3 konumlarındaki alpha=0° hücum açısında, sürüklemekuvvetinde dikkate değer azalmalara ve ısı transferinde önemli artışlara neden olan yüksek girdap kopma frekansınasahip akış yapısı elde edilmiştir. Bu akış yapısının alpha=0^o, ye kadar artan hücum açısı ile azalarak devam ettiğigörülmüştür. Hücum açısının daha da arttırılması ile akış kontrol çubuğunun girdap oluşum yapısı üzerindeki etkisitamamen ortadan kalkmaktadır.

AtıfTR Dizin9

İncele

Akansu, Yahya Erkan; Özmert, Mehmet; Firat, Erhan

In this study, the effect of attack angle on vortex shedding phenomena in the case of flow around the square prism as a bluff body and the circular rod which used as flow control component was experimentally investigated. While the value of attack angle equal to 0 degrees, the upstream control rod and square prism are in tandem arrangement to free stream. Experiments were conducted at Reynolds number of 1.0 x 10(4), for the diameter ratio of d/D=0.25, the attack angle between 0 degrees <= alpha <= 90 degrees, and the value of normalized distance between two prism LID is 1, 2, 3, and 4. The velocity measurements were conducted by means of constant temperature anemometer (CTA) as well as vortex shedding frequencies obtained by the spectral analysis of velocity-time history. Characteristics of the vortex formation region and location of flow attachments, reattachments, and separations were observed by means of the smoke-wire flow visualizations. At the angle of attack 0 degrees of the location L/D=2 and 3, the flow structure that possess high vorex shedding frequency which causes remarkable reductions on the drag force and significant increase in the heat transfer was obtained. This flow structure continous to decrease with increasing attack angle up to around 10 degrees. By further increasing of attack angle, the effect of flow control rod on vortex shedding frequency disappears completely.

AtıfWoS6

İncele

Akansu, Yahya Erkan; Firat, Erhan; Vit, T; Dancova, P

Control of the flow around a square prism by means of synthetic jet through a single slot located on middle of upper surface of the model has been investigated experimentally for Reynolds number of 8000. Synthetic jet was implemented by using a pneumatic piston-cylinder which was driven by means of an electrical motor. The frequency and stroke of the piston were changed to obtain various values of the flow control parameters. For various excitation frequency and momentum coefficients of the synthetic jet, the mean and fluctuating pressure distributions on the square prism were measured. The velocity measurements at the slot exit and at a specific coordinate were conducted by means of constant temperature anemometer (CTA). Vortex shedding frequencies obtained by the spectral analysis of both pressure-time and velocity-time history. At a value of synthetic jet excitation frequency, vortex pairs generated at slot were perturbed the shear layer that separated from the upper leading edge of square model and disturbs it. When the synthetic jet excitation frequency closes enough to the vortex shedding frequency, the lock-in of vortex shedding frequency onto the exciting frequency was occurred. On the other hand, increasing excitation frequency of the synthetic jet causes a pressure recovery on the surface of the prism within the wake region. The efficiency of the synthetic jet is classified depending on change of the drag coefficient and vortex shedding frequency.

AtıfWoS1

İncele