Abstract: To evaluate the unsteadiness of wall pressure in an over-expanded single expansion ramp nozzle，under fixed nozzle pressure ratio (NPR) 7.54 and 9.98，respectively，an experimental investigation has been conducted based on dynamic pressure measurement and focus schlieren techniques. Under bothNPRs，the tests showed free shock separation (FSS) is formed on the lower wall. On the upper wall atNPR=7.54，the separation mode is fully restricted shock separation (RSS). However，the separated shear-layer can come in very close proximity to the lower wall and randomly impinges on it atNPR=9.98，so that wall pressure signal near the nozzle exit randomly alternates between its value in the backflow region and that above ambient，the separation mode is partially restricted shock separation (pRSS). Under different separation modes，the peak frequency of the wall pressure pulsation in the upstream undisturbed zone is close to 6kHz，and near the flow separation point in the nozzle exhibits low broadband frequency oscillation characteristics. In the RSS mode，the wall pressure pulsation near the separation point has a relatively distinct dominant frequency，while in the FSS and pRSS modes，there is no obvious distinct dominant frequency.

摘要： 为获得单边膨胀喷管（SERN）过膨胀状态下壁面压力非定常特性，在喷管落压比（NPR）为7.54和9.98两种状态下，采用动态压力传感器对SERN壁面压力进行试验测量，并结合聚焦纹影观测流场。结果表明：在两种落压比条件下，喷管下壁面分离模态均为自由激波分离（FSS）；NPR=7.54条件下，喷管上壁面分离模态为受限激波分离（RSS）；而在NPR=9.98条件下，喷管上壁面分离剪切层间歇性地撞击喷管壁面，导致喷管出口附近壁面压力间歇性的高于环境压力，流动分离模态为部分受限激波分离（pRSS）。不同分离模态下，上游未受扰动区域壁面压力脉动主频均接近于6kHz，喷管内流动分离点呈现宽低频振荡特性。RSS模态下，分离点附近壁面压力脉动具有相对独立主频，而在FSS和pRSS模态下无明显独立主频。

关键词: 单边膨胀喷管;过膨胀状态;受限激波分离;自由激波分离;低频振荡