# Passive Control of Base Pressure: A Review
## 2 Various Types of Passive Controls
### Passive Control in the Form of Splitter Plate  
The effect of passive control in a splitter plate on a circular cylinder is studied by [PERSON] et al. [24] numerically for laminar flow. A splitter plate was positioned horizontally in the wake region with the same length as the cylindrical diameter. The plate, which  
Figure 13: Square nozzle with threaded spikes control plate [23]. suppresses the vortex shedding, decreased the drag force substantially as well as the lifting fluctuation; for maximum reduction, there is an ideal plate position. However, they increased sharply as the plate was placed further downstream from the optimum position. This finding is consistent with the current experimental observation in the turbulent wake. It is evident that for the steady flow, i.e., at Re = 30, the drag coefficient continuously decreases as there is an increase in the G/d value. For the unsteady flow (Re = 100 and 160), the drag coefficient first slightly increases for \(0\leq\) G/d \(\leq\) 0.25 and continuously decreases for G/d = 2.6. It is observed that the drag coefficient decreases with a higher Reynolds number. A 3% drag reduction is achieved for Re = 100 and 6.7% is achieved for Re = 160 at the optimum location of the plate i.e., G/d = 2.6 in comparison with the cases of no plate i.e., G/d = 0. A numerical study was conducted by [PERSON] and [PERSON] [25] on the triangular cylinder's splitter plate effect. They considered the Reynolds number from 50 to 200 based on the triangular cylinder's side, and the length of the splitter plate is varied from 0 to 6. The passive control in the form of a splitter plate is significant, resulting in a reduction of the drag. Drag is reduced from 9% to 57% by attaching the splitter plate to the triangular cylinder. [25]. It is observed that there is a decrement in skin friction drag with an increment in plate length, and with a further increment in the plate length, the skin friction drag increases. The pressure drag decreases continuously with the plate length increment. Here it is observed that the total drag decrement is observed from 9% to 57%. The splitter plate as a passive control was experimentally studied by placing it near the trailing edge along the wake centerline of a turbulent boundary layer on a flat plate by [PERSON], [PERSON] et al. [26]. The splitter plate length was varied from half to five times the thickness of the trailing edge. The base pressure behind the trailing edge was measured. The mean velocity and pressure distribution measurement on the flat plate in the turbulent boundary layer were made under the freestream zero-pressure gradient. Within an inner layer of the turbulent boundary layer near the trailing edge, the mean velocity without the splitter plate increased more than that in the upstream location. However, the base pressure increases with the splitter plate made the mean velocity distribution similar to that of a fully developed turbulent boundary layer by [PERSON], [PERSON] et al., [26]. It can be observed that when the length of the splitter plate \(<\) 1, the value of C (C = C\({}_{\text{pb}}-\{\text{C}_{\text{pb}(\text{without splitter plate})}\}/({\text{C}_{\text{pb}}})_{\text{without splitter plate}}\)) continuously decreases with the increment in 1/h value. For 1/h = 1, the C has a minimum value of \(-\)0.55. C then increases slightly with changes in 1/h to a maximum value of \(-\)0.52 at 1/h = 2, and above 1/h = 2, C decreases somewhat at higher 1/h, and therefore for 1/h = 4, a constant value of \(-\)0.58 is maintained. Simultaneously, [PERSON] [27] and [PERSON] et al. [28] show some differences when the present data are compared. To reduce fuel consumption and improve road vehicle dynamics, [PERSON] and [PERSON] [29] studied a low Reynolds number of 1.0 \(\times\) 10\({}^{6}\) and 1.6 \(\times\) 10\({}^{6}\) using a splitter plate at its front or rear a simplified car geometry to reduce drag. Utility vehicles or MPV vehicles are considered by representing them in the form of simplified geometry.