## 5 Results  
Table 1 lists TPJB, pivot, and recess geometries and the properties of sCO\({}_{2}\) at the initial condition. The journal diameter and axial pad length are both equal to 25 mm. The four pads, each with an angular extent of 70\({}^{\circ}\), a pad thickness of 8 mm, a pivot offset of 0.5, and a preload factor of 0.5, constitute the TPJB. The pivot is of the rocker-back shape, a cylindrical type whose radius is 18 mm with a housing radius of 21 mm. The rocker-back pivot length is equal to the bearing length (25 mm). Each pad has a rectangular recess whose geometrical center is concentric with the pad's pivot. The recess has a circumferential length of 5 mm (22.9\({}^{\circ}\)), an axial length of 5 mm, and a depth of 0.1 mm, thus covering about 6.67% of the pad area. The orifice at the center of the recess has a diameter of 0.5 mm, and the orifice discharge coefficient is 0.68 [31]. The bearing is lubricated with sCO\({}_{2}\) with an ambient pressure and temperature of 8.0 MPa and 37 \({}^{\circ}\)C, respectively, at which its density and viscosity are 426.6 kg/m\({}^{3}\) and 30.4 uPa-s, respectively. The temperature of the high-pressure sCO\({}_{2}\) supplied through the orifice is similar to that of the ambiance. Note that sCO\({}_{2}\) supplied through the orifice must have a higher pressure than the ambient pressure to pressurize the bearing hydrostatically. Figure 6: Centerline pressure vs. circumferential coordinates (from 220\({}^{\circ}\) to 320\({}^{\circ}\)) for a fixed-pad three-recess hybrid journal bearing compared to the test data reported in Ref. [39]. \(P_{s}\) = 0.4 MPa, and static load = 356 N. Rotor speed = 5 and 8 krpm (hybrid operation). Figure 7 shows plots of the 3D distributions of the (a) pressure, (b) temperature, (c) density, and (d) viscosity of the lubricant (sCO\({}_{2}\)) over each pad for hybrid TPJB with pressurized recesses. The supply pressure of sCO\({}_{2}\) at the orifice is 10 MPa, and the static load applied at 270\({}^{\circ}\) and rotor speed are 100 N and 60 krpm, respectively. Each pad has peak constant pressure at the recess region. The loaded pads (pads 3 and 4) have the highest recess pressure, whereas the unloaded pads (pads 1 and 2) have the lowest values. The temperature is lowest at the pad leading edge and highest at the trailing edge. For each pad, the stepped track from the recess toward the trailing edge is attributed to the cooling effect of the fresh orifice flow. The density and viscosity of sCO\({}_{2}\) are maximum at the recess region. The loaded pads (pads 3 and 4) have the highest values, whereas the unloaded pads (pads 1 and 2) have the lowest values, similar to the case of pressure. Though the density and viscosity of sCO\({}_{2}\) are functions of both pressure and temperature, it mainly follows the trend of the film pressure, as the temperature rise is relatively insignificant owing to the large specific heat of the lubricant. Figure 8 shows the 3D distributions of (a) pressure, (b) temperature, (c) density, and (d) viscosity of sCO\({}_{2}\) over pads for conventional hydrodynamic TPJB without recesses but with a load and speed similar to those in Figure 7. The loaded pads (pads 3 and 4) have the highest hydrodynamic pressure, whereas the unloaded pads (pads 1 and 2) have the lowest pressure. Note the relatively small film pressure on the unloaded pads for the hydrodynamic TPJB compared to that of hybrid TPJB. The film temperature rises from the lowest value at the leading edge of the unloaded pad (pad 1) to the maximum value at the trailing edge of the loaded pad (pad 4). Note that hydrodynamic TPJB has a higher temperature than hybrid TPJB, particularly at the loaded pads; the hydrostatically pressurized fresh fluid flow from the orifice cools the film for hybrid TPJB. Temperature changes in the axial direction are relatively insignificant, as in hybrid TPJs.