# Study on Correction Method of Internal Joint Operation Curve Based on Unsteady Flow
###### Abstract  
The turbocharger, a key component in a vehicle's powertrain, results in insufficient accuracy if it does not fully consider the unsteady flow effects of the intake and exhaust systems. Based on the difference between the turbocharger's actual operating performance with unsteady flow and the corresponding steady flow performance, unsteady flow correction concepts and correction methods for the compressor and turbine were put forward, and the correction of the internal joint operation curve was investigated. The results show that when unsteady correction coefficients were added to both ends of the turbocharger and the optimized structure was used at both ends, the original turbocharger's surge margin was reduced by 4.6% to 11.8%, and that of the optimized turbocharger was reduced by 15.2% to 21.9% in the medium-low-speed range. Meanwhile, the unsteady flow energy utilization coefficient of the optimized turbocharger was more than 14.5% higher than that of the original turbocharger in the medium-low speed range, and the energy utilization advantage was obvious. It indicated that the optimized turbocharger was working earlier, and the engine's medium-low-speed admission performance has been obviously improved. Therefore, compared with the steady curve, the corrected unsteady curve was closer to the actual engine performance. vehicle; powertrain; engine; turbocharger; internal joint operation curve; unsteady flow +
Footnote †: journal: [PERSON] developed a parametric method for designing the hub, casing, and blades of the compressor impeller [16]. [PERSON] proposed an optimal arrangement for a random tip gap and random stagger angle in the case of a whole annulus rotor [17]. In the engine intake process, the inlet pipe is influenced by the cylinder suction when the flow rate increases and the pressure decreases, while the compressor outlet is also influenced by the engine intake fluctuations because it is connected to the engine inlet pipe, making the compressor outlet flow rate and pressure change periodically with the engine operating process [18]. This means that the outlet region of the compressor is at a periodic unsteady flow boundary. [PERSON] investigated the effect of compressor outlet pipe length and volume on the amplitude and frequency of the compressor outlet pulsation using both experimental and simulation methods under surge conditions and concluded that the surge oscillation in the impeller region of the compressor affects the fluctuation of the pressure and flow rate in the downstream pipe of the compressor [19]. [PERSON] performed an unsteady flow analysis of the pressurized airplane before rotating stall conditions to find rotating stall precursors [20]. [PERSON] analyzed the performance of a compressor under unsteady flow and found that the compressor's unsteady flow energy deviated from the corresponding steady state and that the position of the surge line was influenced by the unsteady flow condition [21]. The performance of the turbine also directly affects the operating performance of the turbocharger, which in turn indirectly affects the output efficiency of the engine [22,23]. [PERSON] deduced the radial turbine mass flow rate performance diagram by proposing a new partial empirical model [24]. [PERSON] developed a gasoline engine flow pulse frequency model and comparatively studied the in-phase and out-phase admission modes [25]. Turbocharger turbines are affected by the pulse exhaust of the engine, and both inlet pressure and temperature vary periodically [26,27]. In the pulsed exhaust environment, where the turbine operates under off-design conditions most of the time, it becomes necessary to study and evaluate turbine performance using unsteady flow methods. [PERSON] developed an experimentally validated model and analyzed the non-linear acoustic predictive capability of the model [28]. [PERSON] evaluated the effects of amplitude, frequency, and temporal gradient on energy dissipation by studying the parametric mass flow pulse characteristics [29].